The Animal Parasites of Man (part 3 of 6)

The Animal Parasites of Man (part 3 of 6)

In the simplest form, the rostellum, or top of the head (as in Dipylidium caninum), appears as a hollow oval sac, the anterior part of which, projecting beyond the upper surface of the head, carries several rows of hooks (fig. 186). The entire internal space of the sac is occupied by an elastic, slightly fibrous mass, while the anterior half of the surface of the rostellum is covered by longitudinal fibres and the posterior half by circular fibres. On contraction of the latter the entire mass is protruded through the apical aperture, the surface of the rostellum becomes more arched, and the position of the hooks is, in consequence, altered. The rostellum of the large-hooked Tæniidæ, which inhabit the intestine of man and beasts of prey, is of a far more complicated structure, for, in addition to the somewhat lens-shaped rostellum carrying the hooks on its outer surface, there are secondary muscles grouped in a cup-like manner (fig. 187). Every change in the curvature of the surface of the rostellum induces an alteration in the position of the hooks. In the hookless Tæniidæ the muscular system of the rostellum is altered in a very different manner; in a few forms a typical sucker appears in its place.

The NERVOUS SYSTEM commences in the scolex and runs through the neck and the entire series of proglottids. Within the proglottids it consists of a number of longitudinal nerve fibres of which those at each lateral border are usually the largest. In the Tæniæ the lateral nerves are accompanied both dorsally and ventrally by a thinner nerve (accessory nerve) (fig. 185); on each surface, moreover, between the lateral nerve and the median plane, there are two somewhat stronger bundles (sub-median), so that there is a total of ten longitudinal nerve bundles. They lie externally to the transverse muscle plates, and the lateral and accessory bundles lie externally to the principal excretory vessels, and are everywhere connected by numerous anastomoses and secondary anastomoses; one typical ring commissure is usually found at the posterior border of the segments. In the Bothriocephalidæ the distribution of the nerve bundles is different (for instance, two lie in the medullary layer), or they are split up into a larger number of branches. In the scolex the nerve bundles are connected in a very remarkable manner by commissures with that which is generally termed the central part of the entire nervous system. There occurs normally a commissure between the two lateral nerves; at the same level, the dorsal and ventral median nerves are also connected at each surface as well with each other as with the lateral nerves, so that a hexagonal or octagonal figure is formed. The so-called apical nerves pass from this commissural system anteriorly, embrace the secondary muscular system of the rostellum semicircularly, and form an annular commissure (rostellar ring) at the inner part of the rostellum.

[Illustration: FIG. 187.--Longitudinal section of the head and neck of Tænia crassicollis, showing the lens-shaped muscular rostellum, with two hooks lying in the concentric cup-like mass of muscles. L.m., longitudinal muscles of the neck; L.f., left lateral nerve; G., ganglion; S.c., subcuticular layer; W{1}_, external, W{2}_, internal excretory vessel. 30/1.

The peripheral nerves arise from the nerve bundles as well as from the commissures situated in the scolex; some go direct to the muscles, while others form a close plexus of nerves external to the inner longitudinal muscles, which plexus likewise sends out fibres to the muscles, but principally to numerous fusiform sense organs (fig. 184, Pl.); they lie internal to the subcuticular cells and, piercing the cuticle with their peripheral processes, end as projecting “receptor” hairs. Higher organs of sense are not known.

The EXCRETORY APPARATUS of the Cestodes is similar to that of other flat worms. The terminal (flame) cells, which hardly differ in appearance from those of the Trematodes, are distributed throughout the parenchyma, but are more common in the cortical than in the medullary layer (fig. 184, T.c.). Before opening into a collecting tube, the capillaries run straight, tortuously, or in convolutions, anastomosing frequently with one another or forming a rete mirabile. The collecting tubes, which have their own epithelial and cuticular wall, and which also appear to be provided with muscular fibres, occur typically as four canals passing through the entire length of the worm (fig. 189); they lie side by side, two (a wider thin-walled ventral, and a narrower thick-walled dorsal one) in either lateral field; in the head the two vessels on each side unite by means of a loop, at the posterior extremity they open into a short pyriform or fusiform terminal bladder which discharges in the middle of the posterior edge of the original terminal proglottis.

This primitive type (fig. 189) of arrangement of collective tubes is subject to variation in most Cestodes, in the scolex as well as in the segments. Indeed, even the lumen of the four longitudinal tubes does not remain equal, as the dorsal or external tubes are more fully developed and become thicker, whereas the ventral or internal ones remain thin, and in some species quite disappear in the older segments (figs. 185, 187). Moreover, very frequently connections are established between the right and left longitudinal branches, as in the head, where a “frontal anastomosis” develops, which in the Tæniidæ usually takes the form of a ring encircling the rostellum (fig. 190), and in the segments of a transverse anastomosis at each posterior border, especially between the larger branches, and more rarely between the smaller collecting tubes also (fig. 191).

The so-called “island” formation is another modification, i.e., at any spot a vessel may divide and after a longer or shorter course the two branches reunite, and this may appear in the collecting tubes themselves as well as in their anastomoses. The above-mentioned ring in the frontal commissure of the Tæniidæ is such an island; similar rings also frequently encircle the suckers (fig. 190). In extreme cases (Triænophorus, Ligula, Dibothriocephalus, etc.) this island formation extends to all the collecting tubes and their anastomoses. Instead of two or four longitudinal canals only, connected by transverse anastomoses at the posterior border of the segments, there is an irregular network of vessels, situated in the cortical layer, from which the longitudinal branches, having again subdivided, can only be distinguished at intervals, and even then not in their usual number.

The opening of the longitudinal branches at the posterior end requires more accurate investigation; it is true that a single terminal bladder is mentioned as being present in many species, but this is also disputed; when the original end proglottis has been cast off, the longitudinal branches discharge separately. Some species possess the so-called foramina secundaria, which serve as outlets for the collecting tubes; they are generally at the neck, but may be situated on the segments.

The contents of the excretory vessels is a clear fluid, the regurgitation of which is prevented by the valves present at the points of origin of the transverse anastomoses. The fluid contains in solution a substance similar to guanine and xanthine.

Genital Organs.--With the exception of one genus (Diœcocestus, Fuhrm.), in which the species are sexually differentiated, all the Cestodes are hermaphroditic; the genitalia develop gradually in the segments (never in the scolex), the male organs, as is usual in hermaphroditic animals, forming earlier than the female. The youngest proglottids generally do not exhibit even traces of genitalia: these, as a rule, develop first in the older segments, and the development proceeds onwards from segment to segment. In a few exceptional cases (Ligula) the sexual organs are already developed in the larval stage, but are only functional after the entry of the parasite into the final host.

With the exception of the end portions of the vagina, cirrus and uterus, all the parts of the genital apparatus lie in the medullary layer, except only the vitellaria, which in many species are in the cortical layer. The male apparatus consists of the testes, of which, as a rule, there are a large number,[278] and which lie dorsal to the median plane (fig. 185, T.); a vas efferens arises from each testis, unites with contiguous vasa, and finally discharges into the muscular vas deferens that is situated in about the middle of the segment. According to the position of the genital pore, the vas deferens opens on the lateral margin or in the middle line in the front of the segment; it is much convoluted or twisted, and frequently possesses a dilatation termed the vesicula seminalis. It finally enters the cirrus pouch, which is usually elongated; within the cirrus pouch lies the protrusible cirrus, which is not uncommonly provided with hooklets.

[278] There are, however, tapeworms with only one, others with only two or three testes in each segment.

The male sexual orifice almost always opens with that of the vagina into a genital atrium, the raised border of which rises above the edge of the segment and forms the genital papilla (fig. 191).

The vagina, like the vas deferens, usually runs inwardly and posteriorly, where it forms a spindle-shaped dilatation (receptaculum seminis); its continuation, the spermatic duct, unites with the oviduct, the common duct of the ovaries (fig. 191). The ovaries, usually two in number, are compound tubular glands in the posterior half of the proglottis, which extend into the medullary layer, but ventral to the median plane.

At the origin of the oviduct there is frequently a dilatation provided with circular muscles (suction apparatus), which receives the ovarian cells and propels them forward. After the oviduct has received the spermatic duct the canal proceeds as the fertilization canal, and after a very short course receives the vitelline duct or ducts, and then the numerous ducts of the shell glands (oötype). [Although the nomenclature of these parts varies, we may consider the oviduct as extending from the ovary to the shell gland and as receiving the spermatic duct and then the vitelline duct and the ducts of the shell gland. The short piece into which the shell gland ducts open corresponds to the oötype in the flukes, but in the tapeworms this portion of the canal is seldom dilated. From this point the oviduct is continued as a shorter or longer tube, the uterine canal or true oviduct opening into the uterus proper.--J. W. W. S.] The vitellarium may be single, but often exhibits its primitive duplication more or less distinctly, in which case it is situated at the posterior border of the segments in the medullary layer (fig. 191). The original position of the double organ is, moreover, the same as in the Trematodes, i.e., at the sides of the proglottids, and thence eventually extending more or less on both surfaces (figs. 192 and 194); the gland is then distinctly grape-like and the follicles lie mostly in the cortical layer.

The egg cell that has been fertilized and supplied with yolk cells receives the shell material at the point of entry of the shell gland ducts, and, as a complete egg, then moves onward to the uterus. In those cases in which the uterus in its further course presents a convoluted canal, and may form a rosette (pseudo-phyllidea), there is an external opening which is usually separate from the genital pore, and lies on the same or the opposite surface. In all other cases, however, the uterus terminates blindly and is represented by a longer or shorter sac lying in the longitudinal axis (fig. 191), but in many forms transversely. With the accumulation of eggs it becomes modified in various ways: (1) it sends out lateral branches (fig. 241), or (2) forms numerous isolated sacs (PARENCHYMAL CAPSULES) containing single eggs or groups of eggs (fig. 217); further, (3) in some cases at the blind end one or more special thick-walled cavities are formed (PARUTERINE ORGANS or UTERINE CAPSULES), in which all or most of the eggs are collected, the uterus then undergoing atrophy.

In species in which the uterus lacks an opening, simultaneously with the growth of this organ an atrophy of the male apparatus, at least of the testes and their excretory ducts, takes place; this atrophy also frequently occurs in the female glands, so that the entire mature segments have besides the uterus only traces of the genitalia left.

In the Acoleïnæ the vagina is more or less extensively atrophied, and in any case has no external opening.

A number of genera are distinguished by the duplication of the genitalia in every segment; the genital apparatus in its entirety, or with the exception of the uterus, is double, or the genital glands and the uterus are single, but the cirrus, vas deferens and vagina are double.

On comparing the genitalia of the Trematodes and Cestodes the parts will be found to agree, but the vagina of the Cestodes corresponds with the uterus of the Trematodes, and the uterus of the tapeworms to Laurer’s canal of the Trematodes, which in most of the Cestodes has lost its external orifice.

DEVELOPMENT OF THE TAPEWORMS.

Copulation.--As each proglottis possesses its own genital apparatus, and male as well as female organs are present, the following processes may occur: (1) self- or auto-fecundation (without immissio cirri); (2) self- or auto-copulation (with immissio cirri); (3) cross-copulation between proglottids of the same or different chains (of the same species); and (4) cross-copulation in the same proglottis in species with double genital pores. These various modes have actually been observed.

In those species which lack the vagina (Acoleïnæ) it appears that the cirri, which are always furnished with hooks, are driven into the tissues and for the most part reach the receptaculum seminis.

The eggs of all Cestodes are provided with shells, but the shells, like their contents, vary. In genera that possess a uterine pore the mature eggs frequently do not differ from those of the Distomata; they have a brown or yellow shell of oval form provided with an operculum, and contain a number of yolk cells in addition to the fertilized ovarian cell (fig. 128), but in other genera (with a uterine pore) the lid is absent and the egg-shell is very thin, the eggs of these genera resembling those of Cestodes in which the secretion of the vitellarium is a light albumin-like substance that contains only a few granules, and in which the egg-shell is very delicate and without operculum.

The eggs of Tæniidæ, for example, at first consist of egg-shell (oötype), ovum and yolk cells. The egg-shell is as a rule soft, colourless and frequently deciduous, and the yolk is scanty in amount and contains few granules. The eggs are, moreover, more complicated than this. They enlarge and change their shape and various envelopes are developed around the embryo. The egg-shell proper often disappears, and one or more embryonal envelopes, or protoplasmic layers, arise, so that eventually it is difficult to say whether the whole egg is present, and, if not, what the layers that remain really are.

The embryonal development in most species takes place during the stay of the eggs in the uterus; in other species it takes place after the eggs have been deposited and are in water. Separate cells or a layer of cells always separate from the segmentation cells, as well as from the cells of the developing embryo, and form one or more envelopes round the embryo; usually two such envelopes are formed, the inner one of which stands in intimate relationship with the embryo itself and is often erroneously termed the egg-shell, but more correctly the embryonal shell or embryophore. In some species it carries long cilia, as in Dibothriocephalus latus, by aid of which the young swim about when released from the egg-shell; as a general rule, however, there are no cilia and this envelope is homogeneous, or is composed of numerous rods and is calcified, as in Tænia spp. (fig. 197). The second outer envelope (“yolk envelope”) (fig. 207, 3) lies close within the true (oötype) egg-shell, and remains within it when the embryo hatches out, and in many species, as in Tænia spp., it perishes at the end of the embryonal development with the delicate egg-shell which was formed in the oötype, so that one observes not the entire egg with egg-shell but only the embryo in its embryonal shell, viz., the embryophore (fig. 197, a.).

The embryo (the ONCOSPHERE) enclosed within the embryonal shell (embryophore) is of spheroidal or ovoid form (fig. 197, b.), and is distinguished by the possession of three pairs of spines, a few terminal (flame) cells of the excretory system, and muscles to move the spines.

NO FURTHER DEVELOPMENT of the oncosphere takes place, either in the parent organism or in the open; in fact, in all cases in which the oncospheres are already formed within the proglottids they do not become free, but remain in their shell; it is only when the oncospheres are provided with a ciliated embryophore that they leave the egg-shell, and they even cast this ciliated envelope after having swum about in water by its means for a week or so. Sooner or later, however, all the oncospheres leave the host that harbours the parental tapeworm and reach the open, either still enclosed in the uterus of the evacuated proglottids, after the disintegration of which they then become free, or after being deposited as eggs in the intestine of the host; they then leave it with the fæces. In the former case also, the slightest injury to the mature proglottids while still in the intestine suffices to allow a part of the oncospheres in their embryophores to be released and mingled with the fæces. Here they are the generally, but falsely, so-called Tæniæ “eggs.” For, as stated above, the “yolk” envelope and the true shell deposited in the oötype have before this disintegrated.

In other cases, e.g., Hymenolepis spp., the uterine (oötype) shell persists in fæces (fig. 230).

In any case the oncospheres must be transmitted into suitable animals to effect their further development; in only very rare cases might an active invasion be possible, as, for instance, takes place with the miracidia of many Trematodes. The entry into an animal is, as a rule, entirely passive, that is to say, the oncospheres are swallowed with the food or water. Many animals are coprophagous and ingest the oncospheres direct with the fæces; others swallow them with water, mud, or food contaminated by such fæces. Infection is easily produced artificially by feeding suitable animals with mature proglottids of certain Cestodes or introducing the oncospheres with the food. As the mature tapeworm frequently finds the conditions suitable for its development in only one species of host, or in species nearly related, and perishes when artificially introduced into other hosts, experiment has taught us that to succeed in cultivating the oncospheres certain species of animals are necessary. Thus we are aware that the oncospheres of Tænia solium, which lives in the intestine of man, develop only in the pig, and only quite exceptionally develop into the stage characteristic of all Cestodes--the cysticercus in the wide sense of the word--in a few other mammals. The oncospheres of T. saginata develop further only in the ox; those of T. marginata (of the dog) in the pig, goat, and sheep; those of T. serrata (of the dog) in hares and rabbits; those of Dipylidium caninum (of the dog and cat) in parasitic insects of the dog and cat, etc. It is not unusual that young animals only appear to be capable of infection, while older animals of the same species are not so.

Once introduced into a suitable animal, which is only exceptionally the same individual or belongs to the same species as the one which harbours the adult tapeworm, the oncosphere passes into the larval stage common to all Cestodes, but varying in structure according to the species. In the simplest case--as, e.g., in Dibothriocephalus--such a larva resembles the scolex of the corresponding tapeworm, only that the head, provided with suckers, is retracted within the fore-part of the neck. Such a larval form is known as a plerocercoid (πλήερης, full; κέρκος, tail). They differ from the cysticercoids in being solid larval forms, elongated, tape-like or oval, with the head invaginated. The conditions appear to be similar in Ligula, Schistocephalus, Triænophorus, but here the larvæ are very large, indeed as large in the first-mentioned genera as the tapeworms originating from them, and the sexual organs are already outlined; doubtless, however, this stage is preceded by one that corresponds to the scolex of the genus in question, and which represents the actual larval stage. In such cases the development of the body of the tapeworm from the scolex has already begun within the first or intermediate host; in other cases, except in the single-jointed (monozootic) Cestodes, this only takes place in the definitive host. The direct metamorphosis of the oncosphere into the larval forms termed PLEROCERCOID has hitherto not been investigated, although Ligula, Schistocephalus and Bothriocephalus are very common parasites, but many circumstances point to the conclusions arrived at by us and by other observers. In the larval stages of other tapeworms we can always distinguish the scolex and a caudal-like appendage, vesicular in the cysticerci (fig. 200), compact in the cysticercoids (fig. 231). The scolex alone forms the future tapeworm, the variously formed appendage perishing.

It has now been proved that the appendage, the caudal vesicle, originates direct from the body of the oncosphere, and therefore is primary, and that the scolex only subsequently forms through proliferation on the surface of this appendage. On account of this origin the scolex is generally regarded as the daughter, and the part usually designated as the appendage as the mother, originating from the oncosphere.

Accordingly, two modes of development of the larval stage may be distinguished; in the one case, plerocerci and plerocercoids, the oncosphere changes directly into the scolex, thus forming the body of the tapeworm within the primary host; in the other case, cysticerci and cysticercoids, the scolex only forms secondarily in the transformed body of the oncosphere, which later on perishes, the scolex alone remaining as the originator of the tapeworm colony.

We may summarize briefly what has been said regarding these larval forms. We have, firstly, solid larval forms without any bladder. These arise directly from the oncosphere and are of two kinds, plerocercus and plerocercoid. Plerocercus is a solid globular larva with the head invaginated into the posterior portion. Plerocercoid (fig. 208) is a solid elongated larva also with the head invaginated into the posterior portion, which is sometimes very long. Secondly, we have larval forms with bladders from which the scolices arise thus indirectly from the oncosphere. They are of two kinds, cysticercoid and cysticercus.

Cysticercoid.--The bladder is but slightly developed and is usually absorbed again. The anterior portion is, moreover, retracted into the posterior, and in some cases there is a long or a stumpy tail (figs. 220, 231).

Cysticercus, or true bladder worms. (These may be divided into (1) cysticercus proper, consisting of a bladder and one scolex; (2) cœnurus, a bladder and many scolices; (3) echinococcus, a bladder in which daughter bladders or cysts are developed, and then in these multiple scolices.)

In the case of cysticerci a papilliform invagination forms, projecting into the interior of the bladder (fig. 201). The layer of cells forming the papilla becomes divided into two laminæ, the outer[279] of which forms a kind of investing membrane (receptaculum capitis) for the papilla. The head and suckers are now developed on the walls bounding the axial lumen of the papilla. The papilla eventually evaginates, so that the receptaculum capitis now forms the inner surface of the hollow head, which eventually becomes solid.

[279] I.e., regarded from the interior or centre of the invagination.

Our knowledge of the development of cysticerci in the wide sense of the word is limited almost exclusively to that of a few true “bladder worms” (cysticerci); in other cases we know either only the terminal stage, i.e., the complete larva, or, exceptionally, one of the intermediate stages, but we are not acquainted with a complete series; the description must therefore be incomplete.

We know from feeding experiments that, after the introduction of mature proglottids or of the fully developed ova of Tænia crassicollis (of the cat) into the stomach of mice, the oncospheres escape from the shell in the middle portion of the small intestine, and a few hours later penetrate into the intestinal wall by means of a boring movement; they have been found in this position twenty-seven to thirty hours after the infection. By means of this migration, for which purpose they employ their spines, they attain the blood-vessels of the intestine; indeed, already nine hours after the infection and later they are found in the blood of the portal vein, and in the course of the second day after infection they are found in the capillaries of the liver, which these larvæ do not leave.

Leuckart, in experimental feeding of rabbits with oncospheres of Tænia serrata (of the dog), found free oncospheres in the stomach of the experimental animal, but not in the intestine: however, he came across them again in the blood of the portal vein. The passage through the blood-vessels to the liver is the normal one for those species of Tænia the eggs of which become larvae in mammals; even in those cases in which the oncospheres develop further in the omentum or in the abdominal cavity (Cysticercus tenuicollis, C. pisiformis), there are distinct changes observable in the liver that lead one to the conclusion that there has been a secondary migration out of the liver into the abdominal cavity. Indeed, one must not imagine that the young stages of the Cestodes are absolutely passive; once they have invaded an organ they travel actively, and leave distinct traces of their passage.

In other cases the oncospheres leave the liver with the circulation, and are thus distributed further in the body; they may settle and develop in one or more organs or tissues. Many oncospheres may, by travelling through the intestinal wall, penetrate through it and attain the abdominal cavity direct; some, perhaps, pass also into the lymph stream. Where there are no blood and lymphatic vessels in the intestinal wall, as in insects, the oncospheres attain the body cavity or its organs direct; in short, they never remain in the intestinal lumen itself, and only rarely--as in Hymenolepis murina of the rat--do they remain in the intestinal wall.

When the infection has been intense, and the body is crowded with numerous oncospheres, acute feverish symptoms, are induced, to which the infected animals usually succumb (“acute cestode tuberculosis”); while in other cases the alterations in the organs attacked--as the liver in mice and the brain in sheep--may cause death.

Sooner or later the oncospheres of tapeworms come to rest, and are first transformed into a bladder, which may be round or oval according to the species. The embryonal spines disappear sooner or later, or remain close together or spread over some part of the bladder wall (fig. 200). Their discovery by V. Stein in the bladder worm of the “meal worm” (the larva of a beetle, Tenebrio molitor) first led to the conclusion that bladder worms (cysticerci) actually originate from the oncospheres of Tæniidæ.

The bladder may remain as a bladder, and then by proliferation the scolex forms on its wall (fig. 202), or it may divide into an anterior so-called “cystic” portion and a solid tail-like appendage of various lengths, on which the embryonal hooks are to be found, and this is particularly the case in those larval forms (cysticercoids), e.g., those of Dipylidium caninum, that develop in invertebrate animals, such as Arthropoda.

As mentioned above one may regard the scolex as an individual that originates through proliferation of the wall of the parent cyst, mostly singly, but in those cysticerci that are termed cœnurus (fig. 201) many scolices occur, whereas in those called echinococcus the parent cyst originating from the oncosphere of Tænia echinococcus (of the dog) first produces a number of daughter cysts, which in their turn form numerous scolices. Echinococcus-like conditions also occur in cysticercoids, as, for instance, in those peculiar to earthworms; and similar conditions prevail in a larval form known as Staphylocystis, found in the wood-louse (Glomeris). Thus it happens in these cases that finally one tapeworm egg produces not one, but numerous tapeworms, for, under favourable conditions, each scolex can form a tapeworm.

The rudiment of the scolex appears as a hollow bud, the cephalic invagination usually directed towards the interior of the bladder cavity; on its invaginated surface arise the four suckers, and the rostellum with the hook apparatus is formed in its blind end; we thus get a Tænia head, but with the position of the parts reversed (fig. 201). In many cysticerci the head rises up from the base of the cephalic invagination and is then surrounded by the latter. A more or less elongated piece of neck also develops, and even proglottids may appear, as in Cysticercus fasciolaris (the larva of Tænia crassicollis of the cat) of the Muridæ, a process somewhat analogous to that of Ligula, etc.

The period that elapses from the time of infection till the cysticercus is fully developed varies according to the species; the cysticercus of Tænia saginata requires twenty-eight weeks, that of T. marginata seven to eight weeks, that of T. solium three to four months, and that of T. echinococcus longer still.

With one single exception (Archigetes) the larvæ do not become sexually mature in the organ where they have developed; they must enter the terminal host, a matter that is usually purely passive, the carriers of the larvæ or infected parts of them being usually devoured by other animals. In this manner, for instance, the larvæ (Cysticercus fasciolaris) found in mice and rats reach the intestine of cats; those of the hare and rabbit (C. pisiformis) reach the intestine of dogs; those of the pig (C. cellulosæ) are introduced into man; those of insects are swallowed by insectivorous birds; those of crustaceans are ingested by ducks and other water fowl; perhaps, also, the infection of herbivorous mammals is caused by their accidentally swallowing smaller creatures infected by larvæ. Indeed, the researches of Grassi and Rovelli have taught us that such an intermediate host is not always necessary; Hymenolepis murina of rats and mice in its larval stage lives in the intestinal wall of these rodents, and as a larva it passes into the intestinal lumen and develops into a tapeworm in exactly the same way as the larvæ of other species that reach the intestine of the terminal host by means of an intermediate carrier. Probably this curtailed manner of transmission also occurs in many other species. In some cases the larvæ actively quit the body of the intermediate host, as in the case of Ligula and Schistocephalus, which travel out of the body cavity of infected fish and reach the water, where they may be observed in hundreds in summer, at all events in some localities. The larval stage of Calliobothrium--wrongly termed Scolex--has been observed swimming free in the sea, and the scolices of Rhynchobothrium, without their mother cysts, have been observed free within the tissues of several marine animals. In any case there is almost always a change of hosts, even in the single-jointed Cestodes, for the larva of Caryophyllæus, which lives in fishes of the carp family, is found in limicoline Oligochætes, that of Gyrocotyle (Chimæra) in shell-fish (Mactra), and different conditions can hardly be possible for Amphilina. Archigetes alone becomes sexually mature in the larval stage, but the life-history of this creature is not well known, so that it is not impossible that the attainment of sexual maturity as a larva in invertebrates (Oligochætes) is perhaps abnormal, and somewhat analogous to the maturity of some encysted Trematodes.

The METAMORPHOSIS OF THE LARVA into the tapeworm is rarely accomplished in a simple manner; the transformation, however, is not complex in the single-jointed Cestodes, nor in Ligula and Schistocephalus; the latter is swallowed by birds (Mergus, Anas, etc.), produces eggs after only a few days, and very soon quits the intestine of its terminal host. In all other cases it is the scolex only which, by proliferating at its posterior extremity, forms the proglottids, after having invaded as a larva the intestine of a suitable host. The mother cysts, or what corresponds to them, die, are digested, absorbed, or perhaps even eliminated; on the contrary, segments found on the scolex during the larval stage, also in the case of Cysticercus fasciolaris, are retained. It is not certain whether the larvæ of Dibothriocephalus lose any part.

The time required by the scolex to complete the entire chain of proglottids does not depend only on the number it has to produce, for Tænia echinococcus, which, as a rule, only possesses three or four segments, takes quite as long a time for their growth (eleven to twelve weeks) as T. solium with its numerous segments; T. cœnurus is fully developed in three to four weeks, and the same holds good for Dibothriocephalus latus, which possesses many more segments than the above-mentioned Tænia of the dog. In a number of species it has been possible to determine fairly accurately the average daily growth; for instance, in Dibothriocephalus latus the daily growth is 8 cm., in Tænia saginata 7 cm., etc.

The history of the development of the Cestodes demonstrates that persons and beasts harbouring larval tapeworms have become infected by having swallowed the oncospheres of the species of tapeworm to which they belong. In regard to Hymenolepis murina alone, it is known that the introduction of the oncospheres into those species of animals which harbour the adult tapeworm leads to the formation of the latter after the development of a larval stage in the intestinal wall; nevertheless, only young animals (rats) are capable of infection, for a previous infection, or the presence of mature tapeworms in the intestine, appears to produce a kind of immunity.

BIOLOGY.

In their adult stage, the tapeworms inhabit almost exclusively the alimentary canal of vertebrate animals, with but few exceptions the small intestine, and a few species select definite parts of it. A small number of Rhynchobothriidæ of marine fishes live apparently always in the stomach, while in rays and sharks the spiral intestine is their exclusive site. Bothriocephali generally attach themselves with their head on to the appendices of the pylorus of fishes; other species (Hymenolepis diminuta) occasionally fix their head in the ductus choledochus, and this is more frequent still in the tapeworms of the rock badger (Hyrax), which occasionally penetrate entirely into the biliary ducts. Stilesia hepatica, Wolffh., has so far only been found in the bile-ducts of its host (sheep and goat, East Africa).

In the disease of sheep induced by Cestodes, the worms have been observed also in the pancreas. Specimens found in the large intestines were probably being evacuated.

The Cestodes are looked upon as fairly inert creatures, this opinion having been formed by observing their condition in the cold cadavers of warm-blooded animals. Actually, however, they are exceedingly active, and accomplish local movements within the intestine, for they have been found in the ducts communicating with the bowel, or in the stomach, and may even make their way forward into the œsophagus.

They also invade other abdominal organs through abnormal communications, or through any that may be temporarily open between the intestine and such organs; they thus reach the abdominal cavity or the urinary bladder, or they work their way through the peritoneum.

They produce changes in the intestinal mucous membrane at the place of their attachment, the alterations varying in intensity according to the structure of the fixation organs. The mucous membrane is elevated in knob-like areas by the suckers; the epithelial cells become atrophied or may be entirely obliterated. Dipylidium caninum bores into the openings of Lieberkühn’s glands with its rostellum, dilating the lumen to two or three times its normal size, while the suckers remain fixed between the basal parts of the cells. Species with powerful armatures penetrate deeper into the submucosa, and some that are not provided with exceptionally strong armatures, or are even unarmed, may be actually found with the scolex embedded in the muscles of the intestinal walls or even protruding beyond (Tænia tetragona, Mol., in fowls, etc.). Other species, again, even cause perforation of the walls of the intestine of their hosts.

It is generally assumed that tapeworms, which almost without exception live in the gut of vertebrates, get their nutriment from the gut contents, which apparently they absorb through the whole body surface (cuticular trophopores). In favour of this view is the existence of fat drops in the proglottids, the identity in colour in certain forms between that of the fresh worm and the gut contents and the passage of certain substances derived from medicines (iron and mercury preparation) into the worms in the gut, etc. Whether the suckers are concerned in the absorption of nutriment and to what extent is still questionable.

THE LENGTH OF LIFE OF THE ADULT TAPEWORM certainly varies; as a rule it appears to last only about a year; in other cases (Ligula) it averages only a few days, but we are likewise aware that certain species of Cestodes of man attain an age of several or many years (thirty-five). The natural death of Cestodes often appears to be brought about by alterations in the scolex, such as loss of the hooks, atrophy of the suckers and rostellum, finally the dropping off of the scolex; it is unknown whether a chain of segments deprived of its scolex then perishes or whether it first attains maturity. It has already been mentioned that in a few species the foremost proglottids are transformed into organs of fixation on the normal loss of the scolex.

Abnormalities and malformations are encountered relatively frequently in the Cestodes--such as abnormally short or long segments; the so-called triangular tapeworms, which--if belonging to the Tæniidæ--always possess six suckers; often also club-shaped segments occur between normal ones, or there may be a defect in one segment or in the centre of a number following one another (fenestrated segments); bifurcated chains of segments have likewise been observed, as well as incomplete or complete union of the proglottids, abnormal increase of the genital pores, reversion of the genitalia. Besides the above-mentioned increase of the number of suckers on the scolex (in Tæniæ), there may be a decrease in the number; in other cases the crown of hooks may be absent, or abnormally shaped hooks may be formed.

CLASSIFICATION OF THE CESTODA OF MAN.

Order. *Pseudophyllidea*, Carus, 1863.

Scolex without proboscis or rostellum. Head “stalk” absent.

Scolex never with four, generally with two (or one terminal) bothria.[280] Vitellaria numerous. Uterine opening present. Genitalia do not atrophy when uterus is developed. In large majority of proglottids eggs (or, if formed, their contents) are at the same stage of development.

[280] Bothridia or “phyllidia” are outgrowths from the scolex. They are concave and extremely mobile. By some authors the term “phyllidium” is used for the outgrowth, and the term “bothridium” is restricted to the muscular cup. Bothria, on the other hand, are grooves more or less wide, the musculature of which is only slightly developed and is not separated off internally from the parenchyma. Acetabula, or suckers in the usual sense, are hemispherical cups, without lips and with musculature separated internally from the parenchyma.

Family. *Dibothriocephalidæ*, Lühe, 1902.

Syn.: Diphyllobothriidæ, Lühe, 1910.

Genitalia repeated in each proglottid (polyzootic Cestodes). Ventral and dorsal surfaces flat. Cirrus unarmed. Cirrus and vagina if non-marginal open on the same surface as the uterus. Uterus long, convoluted, often forming a “rosette,” never dilates into a uterine cavity. Eggs thick shelled, operculated, constantly being formed in mature proglottids.

Sub-family. *Dibothriocephalinæ*, Lühe, 1899.

Syn.: Diphyllobothriinæ, Lühe, 1910.

Segmentation distinct. Scolex unarmed, elongated, sharply separated (generally by a neck) from the first proglottis. Cirrus and vagina open ventrally. Genital pores non-alternating. Vas deferens surrounded by a muscular bulb. Receptaculum seminis large, sharply separated from the spermatic duct.

Order. *Cyclophyllidea*, v. Beneden.

Four suckers always present. Uterine opening absent. Vitellarium single. Genitalia atrophy when uterus is fully developed.

Family. *Dipylidiidæ*, Lühe, 1910.

Rostellum if present armed. Suckers unarmed. Uterus breaks up into egg capsules. Paruterine organs absent.

Family. *Hymenolepididæ*, Railliet and Henry, 1909.

Segment always broader than long. Genitalia single. Longitudinal muscles in two layers. Genital pores unilateral. Testes one to four. Uterus persistent, sac-like. Eggs with three shells.

Family. *Davaineidæ*, Fuhrmann, 1907.

Rostellum cushion-shaped. Armed with numerous (sixty to several thousand) hammer-shaped hooks in two (rarely one) rows.

Sub-family. *Davaineinæ*, Braun, 1900.

Suckers armed. Uterus breaks up into egg capsules. Paruterine organs absent.

Family. Tæniidæ, Ludwig, 1886.

Suckers unarmed. Uterus with median longitudinal stem and lateral branches. Female genitalia at the hind end of the proglottis. Genital pore irregularly alternating. Testes numerous in front of female genitalia. Ovary with two lobes (wings). Vitellarium behind the ovary. Embryophore radially striated.

THE CESTODES OF MAN.

Most of the species to be mentioned live in man in their adult stage and occupy the small intestine; man is the definite host of these parasites, but is not the specific host for all the species; some of these species, as well as others (of mammals), may occur in man also in the larval stage.

Family. *Dibothriocephalidæ.*

Sub-family. *Dibothriocephalinæ.*

Genus. *Dibothriocephalus*, Lühe, 1899.

Syn.: Diphyllobothrium, Cobbold, 1858; Bothriocephalus, p. p. Rud., 1819; Dibothrius, p. p. Rud., 1819; Dibothrium, p. p. Dies., 1850.

Scolex egg-shaped; dorsal and ventral bothria elongated, moderately strong, cutting rather deeply into the head; genitalia single in each proglottis; papillæ in the vicinity of the genital atrium; the testes and vitellaria are in the lateral fields, the former in the medullary layer, the latter in the cortical layer on both surfaces, and occasionally extending to the median line; the ovary ventral, the shell gland dorsal. The uterus is in the central field, taking a zigzag course, and frequently forms a rosette.

*Dibothriocephalus latus*, L., 1748.

Syn.: Tænia lata, L., 1748; Tænia vulgaris, L., 1748; Tænia grisea, Pallas, 1796; Tænia membranacea, Pall., 1781; Tænia tenella, Pall., 1781; Tænia dentata, Batsch, 1786; Bothriocephalus latus, Bremser, 1819; Dibothrium latum, Dies., 1850; Bothriocephalus cristatus, Davaine, 1874[281]; Bothriocephalus balticus, Kchnmstr., 1855; _Bothriocephalus latissimus_, Bugn., 1886.

[281] Until recently this worm, which was understood to belong to a separate species, was proved on examination by R. Blanchard (“Mai. Par.,” 1896), to be Dibothriocephalus latus. Compare also Galli-Valerio, in Centralbl. f. Bakt., Path. und Infektionskr., 1900 (1), xxvii, p. 308.

Length 2 to 9 m. or more; colour yellowish-grey; after lying in water the lateral areas become brownish and the uterine rosette brown. The head is almond-shaped, 2 to 3 mm. in length, the dorso-ventral axis is longer than the transverse diameter; the head, therefore, generally lying flat, conceals the suctorial grooves at the borders; these suckers are deep and have sharp edges (fig. 205). The neck varies in length according to the degree of contraction and is very thin; there are 3,000 to 4,200 proglottids and there may be more; their breadth is usually greater than their length, but in the posterior third of the body they are almost square, and the very oldest are not uncommonly longer than they are broad. There are numerous testes situated dorsally in the medullary layer of the lateral fields; the vas deferens (fig. 192) passes dorsally in transverse loops in the central field anteriorly and forms a seminal vesicle before its entry into the large cirrus pouch.

The orifice of the vagina is close behind the orifice of the cirrus; the former passes almost straight along the median line posteriorly, and widens into a receptaculum seminis shortly before its junction with the oviduct; the ovary is bilobed, in shape like the wings of a butterfly, ventrally in the medullary layer; the shell glands lie in the posterior recess of the ovary; the uterus, forming numerous transverse convolutions, passes ventral to the vas deferens forwards. Eggs (fig. 207) large, with brownish shells and small lids, 68 µ to 71 µ by 45 µ; the ovarian cell, which is already, as a rule, in process of segmentation, is surrounded by numerous large yolk cells; the proglottids nearest the posterior extremity are frequently eggless.

The eggs, which are deposited in the intestine and evacuated with the fæces, hatch in water after a fortnight or more; the embryonal integument (embryophore) of the oncosphere is provided with cilia; after bursting open the lid of the egg the oncosphere in its embryophore (fig. 207) reaches the water and swims slowly about; often it slips out of its ciliated embryophore, sinks to the bottom and is capable of a creeping motion; sooner or later it dies in the water. The manner and means of its invasion of an intermediate host are still unknown; yet we are aware that the larval stage (plerocercoid, fig. 208), which resembles the scolex and may reach a length of 30 mm., lives in the intestine, in the intestinal wall, in the liver, spleen, genital glands and muscular system (fig. 209) of various fresh-water fish, the pike (Esox lucius), the miller’s thumb (Lota vulgaris), the perch (Perea fluviatilis), Salmo umbla, Trutta vulgaris, Tr. lacustris, Thymallis vulgaris (grayling), Coregonus lavaretus, C. albula (in Europe) and Onchorhynchus perryi (in Japan). The transmission of the plerocercoids from these fish to the dog, cat and man (Braun, Parona, Grassi and Ferrara, Grassi and Rovelli, Ijima, Zschokke, Schroeder) leads to the development of the broad tapeworm, the growth of which is rapid. In my experiments on human beings the average number of proglottids formed per diem averaged thirty-one to thirty-two for five weeks, with a length of 8 to 9 cm. According to Parona the eggs appear twenty-four days after man has been infected. Zschokke found the average growth in the experimental infection of man between 5·2 and 8·2 cm. per diem, and the person experimented upon by Ijima evacuated a piece of a Dibothriocephalus latus, 22·5 cm. in length, only twenty-one days after the infection.

The “broad tapeworm” is a frequent parasite of man in some districts, but it also occurs in the domestic dog, and on rare occasions is found in the domestic cat (together with Dibothriocephalus felis, Crepl.) and fox. French Switzerland and the Baltic Provinces of Russia are the centres of distribution; from the former districts the distribution radiates to France and Italy (Lombardy, Piedmont); from the Baltic Provinces over Ingermanland to Petrograd, over Finland to Sweden (on the shore of the Gulf of Bothnia), in a southerly direction to Poland, and into the Russian Empire and across it to Roumania, and towards the west along the coast of the Baltic Sea to the North Sea, where, however, its frequency considerably diminishes (Holland, Belgium, and the North of France).

In Turkestan and Japan the “broad tapeworm” is the most frequent parasite of man; it has been reported in Africa from the vicinity of Lake N’gami as well as from Madagascar; cases, in part at least imported, have also come under observation in North America.

In Germany Dibothriocephalus latus--apart from the fact that it is undoubtedly imported from Switzerland, Russia or Italy--is particularly frequent in East Prussia amongst the inhabitants of the Courland Lagoon district, on the Baltic; it is, moreover, also found in the Province and even in the City of Königsberg. In West Prussia and Pomerania it is very much scarcer.

It is also found in Munich and in the vicinity of the Lake of Starnberg (Bollinger).

Krabbe found it in 10 per cent. of the sufferers from tapeworms in Denmark; Szydlowski found the ova of this worm in Dorpat in 10 per cent. of the fæces examined; Kruse found the worm in 6 per cent. of post-mortems; Kessler, in Petrograd, found the eggs in the fæces in 7·8 per cent.; at post-mortems he found the worms in 1·17 per cent., though Winogradoff only found it in 0·8 per cent. In Moscow, according to Baranovsky, 8·9 per cent. of the fæces examined contained the ova of Dibothriocephalus. In the interior and southern provinces of Sweden the worm, according to Lönnberg, is only found sporadically, but, on the other hand, in Angermanland about 10 per cent. of the population is affected; while again in Norbotten the majority of persons are affected, and in Haparanda the entire population (with the exception of infants) harbour this parasite. In Switzerland D. latus is very frequent in close proximity to the lakes of Bieler, Neuchatel, Morat and Geneva (according to Zaeslin 10 to 15 to 20 per cent. of the population are affected); the parasite is less frequent in districts one to four hours removed from these lakes.

Of the fish from Swiss lakes examined by Schor those from Lake Geneva were most commonly infected, and especially Lota sp. and Perea sp.

The frequency and distribution have, nevertheless, decreased perceptibly in places; at the commencement of the eighteenth century the broad tapeworm was very common in Paris, at the present date it only occurs when imported (Blanchard); in Geneva, also, according to Zschokke, it has become rarer (formerly 10 per cent., now only 1 per cent.).

The disturbances produced in man by the presence of broad tapeworms are, as a rule, very trifling; in other cases they produce partly gastric disorders and partly nervous symptoms; in a number of cases, again, they set up severe anæmia, apparently caused by toxins produced by the worms and absorbed by the host. There is no danger of auto-infection, as the larval stage lives only in fishes, not in warm-blooded animals. The case reported by Meschede (ova like those of Dibothriocephalus latus in the brain of a man who had suffered from epilepsy for six years) must be otherwise explained.

Human beings, like other hosts, can only acquire the broad tapeworm by ingesting its plerocercoids with the previously mentioned fresh-water fishes; the opportunity for such infection is afforded the more readily by the fact that not only do the lower classes not pay sufficient attention to the cooking of fish, so that all the larvæ that are present may be killed, but also in certain localities the custom exists of eating some parts of these fishes in a raw condition; even the mere handling of the usually severely infected intermediary hosts may occasionally cause infection. The plerocercoids are as well known as, but differ materially in appearance from, the cysticerci (Cysticercus cellulosæ) of pig’s flesh. In Germany the occurrence of the plerocercoids of Dibothriocephalus latus has been confirmed in the pike, miller’s thumb and perch of East Prussia, and more particularly in those taken from the Courland Lagoon.

The life of D. latus is a very long one (six to fourteen years), as is deduced from persons who have left D. latus regions after they have been infected.

According to the experiments of M. Schor, plerocercoids of D. latus placed in slowly warmed water completely lose their movement at 54° to 55° C.; they survive the death of their host for several days; they are killed by low temperatures -3° to +1° C. in two days; strong acids and salt solutions kill them at once, also high temperatures, but all the same at least ten minutes is required in boiling or frying fish in order to kill the plerocercoids with certainty.

*Dibothriocephalus cordatus*, R. Lkt., 1863.

Syn.: Bothriocephalus cordatus, R. Lkt.

Length, 80 to 115 cm.; the head is heart-shaped and measures 2 by 2 mm. The suctorial grooves are on the flat surface; the segments commence close behind the head and increase rapidly in breadth. At only 3 cm. behind the head they are already mature; the greatest breadth attained by them averages 7 to 8 mm., the length 3 to 4 mm.; the number of proglottids averages 600; the most posterior ones are usually square. The uterine rosette is generally formed of six to eight lateral loops. The eggs are operculated and measure 75 µ by 50 µ.

Dibothriocephalus cordatus is a common parasite of the seal, the walrus and the dog in Greenland and Iceland, occasionally of man also. No doubt its larva lives in fishes.

The statement that D. cordatus also occurs in Dorpat in human beings has been proved erroneous (Zool. Anzeiger, 1882, v, p. 46), as also has the report that this worm lives in hares in the neighbourhood of Berlin, whither it was supposed to have been carried by Esquimaux dogs (Rosenkranz in Deutsch. med. Wochenschr., 1877, iii, p. 620). The parasite stated by the author to be D. cordatus is Tænia pectinata, Goeze, which has been known since 1766.

*Dibothriocephalus parvus*, Stephens, 1908.

Largest gravid segments 5 by 3 mm. Uterus forms a central rosette with four to five loops on each side of median line. In a proglottid measuring 3·5 by 2·25 mm. the genital atrium is situated 0·4 to 0·5 mm. behind the anterior margin and the uterine opening the same distance behind the genital atrium. Calcareous corpuscles absent in the preserved specimens. Eggs operculated, 59·2 µ by 40·7 µ.

Distinguished from Dibothriocephalus latus--(1) by the size of gravid segments (the minimum width of gravid segments of D. latus is 10 to 12 mm., so that D. parvus is a much smaller worm); (2) quadrate segments of D. latus measure 6 by 6 mm., those of D. parvus 4 by 4 mm.; (3) by the eggs.

From D. cordatus it is distinguished by--(1) D. cordatus has only fifty immature segments, D. parvus has at least 200, possibly more; (2) mature segments of D. cordatus measure 7 to 8 mm., maximum width of D. parvus is 5 mm.; (3) quadrate segments of D. cordatus measure 5 to 6 mm.; (4) D. cordatus has six to eight uterine loops; (5) D. cordatus measures 75 µ to 80 µ by 50 µ.

Habitat.--Intestine of man (Syrian, in Tasmania).

Genus. *Diplogonoporus*, Lönnbrg., 1892.

Syn.: Krabbea, R. Blanch., 1894.

The scolex is short and has powerful suctorial grooves; no neck; the proglottids are short and broad; there are two sets of genital organs side by side in each segment, which in all essentials resemble the single one of Dibothriocephalus.

Parasitic in whales and seals, occasionally in man.

*Diplogonoporus grandis*, R. Blanch., 1894.

Syn.: Bothriocephalus sp., Ijima et Kurimoto, 1894; Krabbea grandis, R. Blanch.

Scolex unknown; chain of proglottids over 10 m. in length, 1·5 mm. broad anteriorly, 25 mm. broad posteriorly. The proglottids are very short (0·45 mm.), but 14 to 16 mm. broad. On either side to the right and left of the worm, along the entire ventral surface, there is a longitudinal groove; these grooves are nearer to each other than to the lateral margin; in them lie the genital pores, and they are in the same sequence as in Dibothriocephalus; corresponding to the scanty length (0·45 mm.) of the proglottids, the ovary is only developed transversely; the uterus only makes a few loops. Eggs (fig. 195) thick shelled, brown, 63 µ by 48 µ to 50 µ. This parasite has hitherto been observed twice in Japanese. Similar species are known in Cetacea and seals.

*Sparganum*, Diesing, 1854.

The term Sparganum, invented by Diesing, is used as a group name of larval bothriocephalid Cestodes whose development is not sufficiently advanced to enable them to be assigned to any particular genus.

*Sparganum mansoni*, Cobb., 1883.

Syn.: Ligula mansoni, Cobbold, 1883; Bothriocephalus linguloides, R. Lkt., 1886; Bothriocephalus mansoni, R. Blanch., 1886.

These plerocercoids were discovered in 1882 by P. Manson during the post-mortem on a Chinaman who had died in Amoy, twelve specimens being found beneath the peritoneum and one free in the abdominal cavity. Cobbold described them as Ligula mansoni, and Leuckart, who contemporaneously reported a case in Japan, termed them Bothriocephalus liguloides. Ijima and Murata reported eight further cases, and Miyake records nine further cases, seven of which are recorded in Japanese literature.

The plerocercoid, which hitherto alone is known to us, attains a length of 30 cm. and a breadth of 3 to 6 to 12 mm. The ribbon-shaped body is wrinkled, the lateral borders are often somewhat thickened, so that the transverse section has the form of a biscuit; the anterior end is usually wider and has the head provided with two weak suctorial grooves, either retracted or protracted.

The parasite makes migrations within the body, and thus may reach the urinary passages; then it is either evacuated with the urine or has to be removed from the urethra; not rarely it causes non-inflammatory tumours on various parts of the skin, which are at times painful and at times vary in size.

Nothing is known of its development and origin.

*Sparganum proliferum*, Ijima, 1905.

Syn.: Plerocercoides prolifer, Ijima, 1905; Sparganum prolifer, Verdun, Manson, 1907.

These plerocercoids produce an acne-like condition of the skin. The condition is really one of capsules in great abundance in the subcutaneous tissue and less so in the corium and in the intermuscular connective tissue. The encapsuled worms in the corium feel like embedded rice grains and raise the epidermis, giving rise to an acne-like condition. Many thousands occur scattered over the body; in Ijima’s Japanese case there were over 10,000 in the left thigh. The worms when they first appear in the skin cause itching. The capsules are ovoid, generally about 1 to 2 mm. in diameter, but they may be smaller and also much larger. The larger ones occur in the subcutaneous tissue. The capsules consist of dense tough connective tissue.

Each capsule, as a rule, contains one worm, but as many as seven may occur. The skin of areas that have been long infected is swollen and indurated or adherent, giving a somewhat elephantoid appearance. The subcutaneous tissue is thick and filled with slimy fluid or in other parts sclerosed.

The Worm.--The chief peculiarity is its irregular shape and its reproduction in the larval stage by forming supernumerary heads, which are supposed to wander about the body.

The simplest forms are thread-like bodies, flat or round, 3 mm. long and 0·3 mm. in diameter, but they may be 12 mm. long by 2·5 mm. broad. The narrow end is the head, which in life invaginates and evaginates, but there is no indication of any suckers, except an inconstant terminal depression. In addition to these simple forms the most complicated and irregular forms occur, due to the formation of buds (heads) at various parts. The detachment and growth of a head account for the presence of more than one worm in a cyst. The irregularity in form is also increased by the presence in the subcuticular tissue of the worm of reserve food bodies. These bodies are supposed to be of this nature and are spherical, 100 µ to 300 µ in diameter, but also much elongated.

Calcareous bodies in the Japanese worms were 7·5 µ to 12 µ; in the Florida worms 8·8 µ to 17·6 µ.

Mode of Infection.--Probably from eating uncooked fish.

Distribution.--Japan, Florida.

Family. *Dipylidiidæ*, Lühe, 1910.

Genus. *Dipylidium*, R. Lkt., 1863.

Rostellum retractile, with several rings of alternating hooks; the latter with a disc-like base, having the shape of the thorns of a rose. Genital pores opposite; genitalia double. Testes very numerous in the central field; ovary with two lobes; the vitellaria, which are smaller, behind them; the uterus forms a reticulum, in the network of which the testicular vesicles lie; later on it breaks up into sacs enclosing one or several eggs. The eggs have a double shell.

*Dipylidium caninum*, L., 1758.

Syn.: Tænia canina, L., 1758, p. p.; Tænia moniliformis, Pallas, 1781; Tænia cucumerina, Bloch, 1782; Tænia elliptica, Batsch, 1786; Dipylidium cucumerinum, Lkt., 1863.

This worm measures 15 to 35 cm. in length and 1·5 to 3 mm. in breadth. The scolex is small, rhomboidal, and has a club-shaped rostellum on which there are, in three to four rings, forty-eight to sixty hooks resembling rose thorns, the size of those in the foremost being 11 µ to 15 µ and those in the hindmost ring 6 µ. The neck is very short, the most anterior segments broad and short, the middle as long as they are broad; the mature segments are longer than wide (6 to 7 mm. by 2 to 3 mm.), fairly thick, are frequently of a reddish colour, and when cast off resemble cucumber seeds. The genital pores lie symmetrically at the lateral margins; the roundish egg sacs, arising from the uterine reticulum, contain eight to fifteen eggs embedded in a reddish cement substance (in life). The eggs are globular (43 µ to 50 µ,); the embryonal shell (embryophore) is thin, the oncosphere measures 32 µ to 36 µ. Surrounding the embryophore is an albuminous coating, and outside this the thin vitelline envelope (fig. 218).

Dipylidium caninum is a common intestinal parasite of dogs, in which it grows larger (Tænia cucumerina, Bloch) than in cats (T. elliptica, Batsch); it has, however, also been found in jackals, as well as in human beings, though in the latter it is of comparatively rare occurrence (twenty-four cases), and almost always affects children, generally of tender age. One-third of all the cases in children were sucklings, about a quarter of all the cases recorded were adults, and these occurred throughout all Europe with the exception of Spain and Italy.

The proglottids, which leave the intestine spontaneously, are recognizable by the naked eye on account of their form and reddish colour, as well as their two genital pores. As a rule, the presence of this parasite sets up no marked symptom in the patient.

The corresponding larval form (cysticercoid) lives in the louse of the dog (Trichodectes canis), a fact that was first established by Melnikow and Leuckart; according to Grassi and Rovelli, as well as Sonsino, it also lives in the flea of the dog (Ctenocephalus canis) and in the flea of man (Pulex irritans), but not in its larva. The adult segments, which also leave the rectum of dogs and cats spontaneously, creep about around the anus and get into the hair, and are thus partly dried and disintegrated. Part of the segments, or the oncospheres released by disintegration, are then taken up by lice and fleas, within which they develop into larvæ (cysticercoids). Dogs and cats are thus infected by their own skin parasites, which they bite and swallow whilst gnawing at their fur. The infection of human beings must occur in an analogous manner, by transmission of the cysticercoids present on the lips or tongue of dogs when the latter lick them, or it may be that the vermin of cats and dogs harbouring cysticercoids are accidentally and directly swallowed by human beings.

Family. *Hymenolepididæ*, Railliet and Henry, 1909.

Genus. *Hymenolepis*,[282] Weinland, 1858.

[282] The genus is by some authors divided into two sub-genera--Hymenolepis, s. str., and Drepanidotænia, Raill.

Drepanidotænia.--Body, broad lanceolate, testes three, female genitalia antiporal beside the testes. Scolex small, with eight hooks. Neck very short, longitudinal muscle bundles very numerous. No accessory sac opening into genital atrium.

Hymenolepis.--Narrow, female genitalia ventral to or between testes.

Accessory sac (opening into genital atrium) usually absent. Vas deferens with an external (outside cirrus sac) and an internal (inside cirrus sac) “seminal vesicle.” Three testes in each proglottis. The eggs are round or oval with two to four distinct envelopes. In mammals and birds.

*Hymenolepis nana*, v. Sieb., 1852.

Syn.: Tænia nana, v. Sieb., 1852, nec van Beneden, 1867; Tænia ægyptiaca, Bil., 1852; Diplacanthus-nanus, Weinld., 1858; Tænia (Hymenolepis) nana, Lkt., 1863.

The worm is 10 to 45 mm. in length and 0·5 to 0·7 mm. in breadth; the head is globular, 0·25 to 0·30 mm. in diameter. The rostellum has a single circlet consisting of twenty-four or twenty-eight to thirty hooks, which are only 14 µ to 18 µ in length. The neck is moderately long; the proglottids are very narrow, up to 200 in number, 0·4 to 0·9 mm. in breadth, and 0·014 to 0·030 mm. in length. The eggs are globular or oval, 30 µ to 37 µ to 48 µ; the oncospheres measure 16 µ to 19 µ in diameter, with two coats, separated by an intervening semi-fluid substance (fig. 224).

This species was discovered by Bilharz in Cairo in 1851; it was found by him in great numbers in the intestine of a boy who had died of meningitis. For several years this was the only case, until 1885, since when numerous cases have come to light. Spooner (1873) even reported a case from North America, which may, however, have related to Hymenolepis diminuta. In Europe the worm is particularly frequent in Sicily, but it has also been repeatedly observed in North Italy; it has, moreover, been reported from Russia, Servia, England, France, Germany, North and South America, the Philippines, Siam and Japan, in all over 100 cases. Notwithstanding its small size this worm causes considerable disorders in its hosts--mostly children--as it sets up loss of appetite, diarrhœa, various nervous disturbances, and even epilepsy; all these symptoms, however, disappear after the expulsion of the parasites, which are generally present in large numbers.

The development as well as the manner of infection is still unknown; Grassi is of opinion that Hymenolepis nana is indeed merely a variety of Hymenolepis murina, Duj., which lives in rats. According to Grassi direct development takes place with omission of the intermediate host, but with the retention of the larval stage; that is to say, rats infect themselves directly with Hymenolepis murina, by ingesting the mature segments or oncospheres of this species, from which subsequently the small larvæ originate in the intestinal wall (fig. 225); when fully developed they fall into the intestinal lumen and become tapeworms. The identity of the two forms has nevertheless been disputed (Moniez, R. Blanchard, v. Linstow), though their near relationship cannot be denied. Grassi gave mature segments of Hymenolepis murina to six persons, but only one person evacuated a tapeworm. This, however, proves nothing in a district where Hymenolepis nana frequently occurs in man; it was, moreover, not possible to infect rats with segments of Hymenolepis nana (of man). Accordingly this form may represent an independent species, which, however, like Hymenolepis murina, also omits an intermediate host.

*Hymenolepis diminuta*, Rud., 1819.

Syn.: Tænia diminuta, Rud., 1819; Tænia leptocephala, Crepl., 1825; Tænia flavopunctata, Weinld., 1858; Tænia varesina, E. Parona, 1884; Tænia minima, Grassi, 1886.

This species measures 20 to 60 cm. in length, and up to 3·5 mm. in breadth; there are from 600 to 1,000 segments. The head is very small (0·2 to 0·5 mm.), it is club-shaped and has a rudimentary unarmed rostellum; the neck is short; the mature segments are 3·5 mm. in breadth, 0·66 mm. in length; the eggs are round or oval. The outer egg-shell is yellowish and thickened, with indistinct radial stripes; the inner embryonal shell (embryophore) double, thin; the outer layer is somewhat pointed at the poles; oncosphere 28 µ by 36 µ. Between the inner and outer shells is a middle granular layer.

Hymenolepis diminuta lives in the intestine of rats--Mus decumanus (the sewer rat), Mus rattus (the black rat), and Mus alexandrinus, rarely in mice; it is occasionally also found in human beings.

Weinland described it from specimens collected by Dr. E. Palmer in 1842, in Boston, from a child aged 19 months, as T. flavopunctata. A second case relating to a three year old child, from Philadelphia, was only reported in 1889 by Leidy; a third case was simultaneously reported of a two year old girl in Varese (T. varesina); and Grassi described another case relating to a twelve year old girl from Catania (Sicily). Sonsino and Previtera reported the same species in Italy, Zschokke in France, Lutz and Magalhães in South America, and Packard in North America: a total of twelve cases, five from America, the rest from Europe (Ransom).

According to Grassi and Rovelli the larval stage lives in a small moth (Asopia farinalis), as well as in its larva, in an orthopteron (Anisolabis annulipes), and in coleoptera (Acis spinosa and Scaurus striatus). Experimental infections have been successful on rats as well as on human beings. In America other species of insects may be the intermediary hosts.

Nicoll and Minchin[283] found in the body cavity of 4 per cent. of rat fleas (Ceratophyllus fasciatus) the cysticercoid of Hymenolepis diminuta. That it belonged to this species was shown by its unarmed rostellum and by feeding; 340 fleas were fed to white rats and fourteen worms obtained, i.e., about 4 per cent., thus corresponding to the infection of the fleas. The development in the flea probably begins in the pupal stage, the eggs being ingested by the older flea larvæ. The larva is 0·31 by 0·25 mm.; tail 0·8 mm., scolex 0·075 by 0·09 mm., suckers, 0·055 mm. in diameter. Microscopically it shows--(1) externally a radially striated layer resembling cuticle, (2) a layer of columnar cells, (3) parenchymatous layer continuous with the tail, (4) fibrous layer around the small caudal vesicle, then the parenchymatous scolex at the bottom of the secondary cavity.

[283] Proc. Zool. Soc., 1911, p. 9.

Nicoll and Minchin (loc. cit.) found a cysticercoid[284] in the rat flea Ceratophyllus fasciatus which was probably that of Hymenolepis murina. Body 0·16 mm., tail 0·19 mm., scolex 0·096 mm. in diameter. Rostellum has twenty-three spines in a single row. Length 0·017 mm., handle 0·01 mm., guard 0·007 mm., prong 0·007 mm. Sucker 0·042 mm. Although this cycle, then, for H. murina also exists, it is not probable that rats (or man in the case of H. nana if this be considered distinct) infect themselves in this way, as they hardly ingest all the necessary fleas to account for the massive infection which frequently exists in rats (and man), so that Grassi’s cycle holds good as the predominant method. Xenopsylla cheopis has also been found by Johnston to harbour both cysticercoids in Australia.

[284] A third cysticercoid resembling this, but without hooks, has also been found.

*Hymenolepis lanceolata*, Bloch, 1782.

Syn.: Tænia lanceolata, Bloch, 1782; Drepanidotænia lanceolata, Railliet, 1892.

The parasite measures 30 to 130 mm. in length and 5 to 18 mm. in breadth; the head is globular and very small; the rostellum is cylindrical, with a circlet composed of eight hooks (31 µ to 35 µ in length). The neck is very short. The short segments increase gradually and equally in breadth, but only a little in length; the female glands lie on the side opposite to that on which the genital pore is situated; the three elliptical testes are on the same side as the pores; the cirrus is armed and slender. The eggs have three envelopes and are oval (50 µ by 35 µ), the external envelope is thin, the middle intermediate layer or envelope is not so marked as in H. diminuta, and the internal one is very thin and sometimes has polar papillæ, as in Hymenolepis diminuta and H. nana.

It inhabits the intestine of the following birds: Domesticated ducks and geese, the Muscovy duck (Cairina moschata), white-headed duck (Erismatura leucocephala), the pochard (Nyroca rufina), and the flamingo (Phœnicopterus antiquorum). It has been recorded from Great Britain, France, Denmark, Austria and Germany.

Zschokke reports the receipt of two specimens which a twelve year old boy in Breslau evacuated spontaneously at two different times.

The corresponding larva, according to Mrázek, lives in fresh water Cyclops; according to Dadai it is likewise found in another copepod, Diaptomus spinosus, but the hooks of Dadai’s larva differed in size.

Family. *Davaineidæ*, Fuhrmann, 1907.

Sub-family. *Davaineinæ*, Braun, 1900.

Genus. *Davainea*, R. Blanch., 1891.

The large scolex is more or less globular, much wider than the rostellum, which is furnished with two rings of very small and numerous hooks. Neck absent, proglottids few, genitalia single. Parasitic chiefly in birds.[285]

[285] [The larval stage of the Davaineas occurs in slugs (Limax) and snails (Helix).--F. V. T.]

*Davainea madagascariensis*, Davaine, 1869.

Syn.: Tænia madagascariensis, Dav.; Tænia demerariensis, Daniels, 1895.

This worm measures 25 to 30 cm. in length; the head has four large round suckers; the rostellum has ninety hooks (18 µ in length); there are 500 to 700 segments, of which the last 100 are filled with eggs and form half of the entire worm. The segments, when mature, measure 2 mm. in length by 1·4 mm. in breadth; genital pores unilateral; about fifty testes; the uterus consists of a number of loops, which at each side are rolled up into an almost spherical ball; when filled with eggs the convolutions unwind, permeate the segment and then lose their wall; the eggs lying free in the parenchyma become finally surrounded, one, or several together, by proliferating parenchymatous cells; this is how the 300 to 400 egg masses, taking up the entire mature segment, are formed. The globular oncosphere (8 µ) is surrounded by two perfectly transparent shells, the outer of which terminates in two pointed processes.

Davainea madagascariensis has hitherto been found in man only (eight times). Davaine described this species from fragments sent to him from Mayotta (Comoro Islands), which were found in two Creole children. Chevreau observed four cases in Port Louis (Mauritius), likewise in children; Leuckart received the first perfect specimen--it was obtained from a three year old boy, the son of a Danish captain, in Bangkok; Daniels, at the post-mortem of an adult native of George Town, Guiana, found two specimens (Tænia demerariensis); and finally Blanchard describes another perfect specimen which was in Davaine’s collection of helminthes in Paris, and which was obtained from a little girl 3 years old, of Nossi-Bé (Madagascar). The intermediate host is unknown.

*Davainea (?) asiatica*, v. Linst., 1901.

Syn.: Tænia asiatica, v. Linstow.

There exists only one headless specimen of this species, which is not quite adult, and which is preserved in the Zoological Museum of the Imperial Academy of Science in Petrograd. It came from a human being and was found by Anger in Aschabad (Asiatic Russia, near the northern frontier of Persia). The specimen measures 298 mm. in length. The breadth anteriorly is only 0·16 mm., the posterior part measures 1·78 mm. across. The number of segments is about 750. The genital pores are unilateral; the testes are globular and lie in a dorsal and ventral layer in the medullary layer; the cirrus pouch is pyriform, 0·079 mm. in length and 0·049 mm. in breadth; the female glands lie in the fore-part of the segments, the ovary reaching to the excretory vessels; the vitellarium is small and round. The vagina has a large fusiform receptaculum seminis; the uterus breaks up into sixty to seventy large, irregularly polyhedric eggsacs.

Family. *Tæniidæ*, Ludwig, 1886.

Genus. *Tænia*, L., 1758.[286]

With the characters of the family. In the genus Cladotænia recognized by some authors, the testes encroach on the mid field and the uterine stem reaches the anterior end of the segment.

[286] The Greeks termed the tapeworms ἕλμινθες πλατεῖαι, more rarely χηρία (= fascia); the Romans called them tænia, tinea, tæniola, later lumbrici, usually with the addition lati, to distinguish them from the Lumbrici teretes (Ascaridæ). The proglottids were called Vermes cucurbitini; the cysticerci χάλαζαι (hailstones), later hydatids. Plater (1602) was the first to differentiate Tænia intestinorum (= Bothriocephalus latus) amongst the Lumbrici lati of man from Tænia longissima (= Tænia solium). The term solium was already used by Arnoldus Villanovanus, who lived about 1300; and, according to him, it signifies “cingulum” (belt, chain), while N. Andry, in 1700, traces this word from “solus,” because the worm occurs always singly in man. Leuckart and Krehl derive the word “solium” from the Syrian “schuschl” (the chain), which in Arabian has become “susl” or “sosl,” and in Latin has become “sol-ium.” What Linnæus described under the term Tænia solium was really Tænia saginata; the latter was first distinguished by Goeze, but was forgotten until Küchenmeister, in 1852, again called attention to the differences.

*Tænia solium*, L., p. p., 1767.

Syn.: Tænia cucurbitina, Pall., 1781; Tænia pellucida, Goeze, 1782; Tænia vulgaris, Werner, 1782; Tænia dentata, Gmel., 1790; Halysis solium, Zeder, 1800; Tænia humana armata, Brera, 1802; Tænia (Cystotænia) solium, Lkt., 1862.

The average length of the entire tapeworm is about 2 to 3 m., but may be even more; the head is globular, 0·6 to 0·8 to 1·0 mm. in diameter. The rostellum is short with a double circlet of hooks, twenty-two to thirty-two in number, usually twenty-six to twenty-eight; large and small hooks alternate regularly; the length of the large hooks is 0·16 to 0·18 mm., of the small ones 0·11 to 0·14 mm. The rostellum is sometimes pigmented. The suckers are hemispherical, 0·4 to 0·5 mm. in diameter. The neck is fairly thin and long (5 to 10 mm.). The proglottids, the number of which averages from 800 to 900, increase in size very gradually; at about 1 m. behind the head they are square and have the genitalia fully developed. Segments sufficiently mature for detachment measure 10 to 12 mm. in length by 5 to 6 mm. in breadth. The genital pores alternate fairly evenly at the lateral margin a little behind the middle of each segment. The fully developed uterus consists of a median trunk, with seven to ten lateral branches at either side, some of which are again ramified. The eggs are oval, the egg-shell very thin and delicate; the embryonal shell (embryophore) is thick, with radial stripes; it is of a pale yellowish colour, globular, and measures 31 µ to 36 µ in diameter; the oncospheres, with six hooks, are likewise globular, and measure 20 µ in diameter (fig. 238).

Malformations are not so common as in T. saginata; they consist in two or several proglottids being partly or entirely fused, formation of single club-shaped segments, fenestration of long or short series of segments and so-called double formation, in which the head has six suckers and the segments exhibit a *Y*-shaped transverse section. The oncospheres occasionally also possess more than six hooklets. Very slender specimens have led to the description of a particular species or variety (T. tenella).

In its fully developed condition T. solium is found exclusively in man; the head is usually attached in the anterior third of the small intestine and the chain, in numerous convolutions, extends backwards; a few mature detached proglottids usually lie at the most posterior part, and these are usually evacuated during defæcation. In exceptional cases single proglottids or whole worms may reach contiguous organs if abnormal communications with them exist; thus they may reach the abdominal cavity and the urinary bladder, or they may be found in a so-called worm abscess of the peritoneum; occasionally, in vomiting, single segments or several together may be brought up. Exceptionally it induces severe anæmia.

The larval stage (Cysticercus cellulosæ) that gives rise to Tænia solium lives normally in the intramuscular connective tissue and other organs of the domestic pig, but it is known to exist also in a few other mammals, such as the wild boar, the sheep,[287] the stag, dog, cat, brown bear and monkey, as well as in man. The cysticercus of the pig is an elliptical vesicle with a longitudinal diameter of 6 to 20 mm., and a transverse diameter of 5 to 10 mm.

[287] The larvæ which on rare occasions are found in the muscular system of sheep are either strayed specimens of Cysticercus tenuicollis, which normally develop in organs of the abdominal cavity, and appertain to Tænia marginata of the dog, or actually Cysticercus cellulosæ. (Cf. Bongert, in Zeitschr. f. Fleisch- u. Milchhyg., 1899, ix, p. 86.)

Even with the naked eye a white spot may be observed in the centre of the long equator, this being the invaginated head; it is easy to make it project by pressing on the vesicle (after tearing off with the finger-nail the investing connective tissue), and on examining it under the microscope one can convince oneself that it corresponds with the head of Tænia solium.

Numerous experiments have proved that the Cysticercus cellulosæ of the pig, if introduced into the intestine of man, grows to a Tænia solium (Küchenmeister, 1855; Humbert, 1856; Leuckart, 1856; Hollenbach, 1859; Heller, 1876); the cysticercus has frequently also been cultivated purposely by feeding pigs with mature proglottids of T. solium (P. J. van Beneden, 1853; Haubner and Küchenmeister, 1855; Leuckart, 1856; Mosler, 1865; Gerlach, 1870; etc.), but success did not attend the efforts to make Cysticercus cellulosæ establish themselves in the intestines of pigs, dogs, guinea-pigs, rabbits and monkeys (Macacus cynomolgus), and so become adult Tæniæ; the attempts, also, to infect dogs with cysticerci by means of ova were likewise, as a rule, abortive.[288]

[288] According to Gerlach only young pigs (up to 6 months old) are capable of infection, and perhaps the failure may have been due to the animals chosen for experiment being of the wrong age.

The development of Cysticercus cellulosæ takes two and a half to three or four months; it is not known how long the cysticerci remain alive in animals; not uncommonly they perish at earlier or later stages, and become calcified or caseated. Extracted cysticerci die in water at a temperature of 47° to 48° C., in flesh at normal temperature they remain alive for twenty-nine days or more. On account of the present rapid means of pickling and smoking meat, the cysticerci as a rule are not killed, also the effect of cold on them for some time in cold chambers of slaughterhouses is not lethal, but freezing is fatal (Ostertag).

There is not the least doubt that human beings are almost exclusively infected with Tænia solium by eating pork containing cysticerci in a condition that does not endanger the life of the cysticerci. The infection may likewise be caused in man by eating the infected meat of other animals subject to this species of bladder worm, mainly, as a matter of fact, deer and wild boar.

The frequency of cysticerci in pigs’ flesh has considerably decreased since the introduction of meat inspection; in the Kingdom of Prussia there was on an average 1 infected pig to every 305 slaughtered between 1876 to 1882; from 1886 to 1889, there was 1 to 551; from 1890 to 1892, there was 1 to 817; in 1896, 1 to 1,470; and in 1899, 1 to 2,102; in the Kingdom of Saxony in 1894 there was 1 infected pig to every 636; in 1895 there was 1 to every 2,049, and in 1896 only 1 infected pig was found of 5,886 slaughtered. In South Germany pigs with cysticerci are very rare, but are more frequent in the eastern provinces of Prussia; in 1892 the number of infected pigs compared with the total slaughtered was as follows:--

In the district of Marienwerder 1 : 28 " " Oppeln 1 : 80 " " Königsberg 1 : 108 " " Stralsund and Posen 1 : 187 " " Danzig, Frankfort a. O. and Bromberg 1 : 250 As compared with the district of Arnsberg 1 : 865 " " " Coblenz 1 : 975 " " " Düsseldorf 1 : 1,070 " " " Münster and Wiesbaden 1 : 1,900

The average for the whole of Prussia in the same year was 1 : 1,290; for the eastern provinces, on the other hand, 1 : 604. Even more unfavourable are the proportions in Russian Poland (over 1 per cent. of pigs measly), in Prague (over 3 per cent.), in Bosnia and Herzegovina (6 to 7 per cent.). The cause for this is most likely attributable to the manner in which the pigs are kept. When allowed to be in the farmyards of the small farmers for the whole day, or allowed to wander in the village streets and pasture lands, they are more liable to take up the oncospheres of the T. solium than when shut up in good pig-styes.

The geographical distribution of T. solium generally corresponds with that of the domestic pig and the custom of eating pork in any form insufficiently cooked or raw. There are, or were, some isolated districts in Germany, France, Italy and England where the “armed tapeworm” was frequent (for instance, Thuringia, Brunswick, Saxony, Hesse, Westphalia, whereas it is and was very scarce in South Germany); it is thus easily understood why it occurs very rarely in the East, in Asia and in Africa, in consequence of the Mahommedans, Jews, etc., not eating pork. In North America, also, T. solium is very rare; the tapeworm which is known there by this name is generally T. saginata, Stiles. During the last decade T. solium infection has, however, very markedly decreased in North and East Germany in consequence of the precautions exercised by the public in the choice of pork to avoid trichinosis, especially, however, because measly meat must be sold as such and must be thoroughly cooked before being placed on the market; indeed, if badly infected it may not be sold for food, but can be turned to account for industrial purposes.

The occurrence of Cysticercus cellulosæ in man has been known since 1558 (Rumler, Obs. med., liii, p. 32); there is hardly an organ in man in which cysticerci have not been observed at some time; they are most frequently found in the brain,[289] where they grow to a variety known as Cysticercus racemosus; next in frequency they are found in the eye, in the muscular system, in the heart, in the subcutaneous connective tissue, the liver, lungs, abdominal cavity, etc. The number of cysticerci observed in one man varies between a few and several thousands. Of the sexes, men are most subject (60 to 66 per cent. of the number attacked). The disturbances caused in man by cysticerci vary according to the nature or position of the organs attacked; when situated in the cerebral meninges they have the same effect as tumours.

[289] Dressel, for instance, examined eighty-seven persons suffering from cysticercus, and found it seventy-two times in the brain, thirteen times in the muscles; K. Müller, in thirty-six cases, found it twenty-one times in the brain, twelve times in the muscles, three times in the heart; Haugg, in twenty-five cases, found it thirteen times in the brain, six times in the muscles, twice in the skin, etc. According to Graefe, amongst 1,000 ophthalmic cases in Halle and Berlin, there was one with cysticercus in the eye; in Stuttgart there was only one in 4,000, in Paris one in 6,000, and in Copenhagen one in 8,000.

During the last decades, however, these cases have also become less common. In Rudolphi’s time 2 per cent. of post-mortems in Berlin showed cysticerci; in the ’sixties, according to Virchow, about the same; in 1875 the number fell to 1·6 per cent.; in 1881 to 0·5 per cent.; in 1882 to 0·2 per cent.; in 1900 to 0·15 per cent., and in 1903 to 0·16 per cent. Hirschberg between 1869 and 1885 discovered cysticerci in the eye seventy times in 60,000 ophthalmic cases, but during the following six years the parasite was only present twice amongst a total of 46,000 cases of ophthalmic diseases, and since 1895 no ophthalmic case has been met with.

The infection of human beings with the cysticerci can only take place by the introduction of the oncospheres of Tænia solium into the stomach with vegetable foods, salads that have been washed in impure water containing oncospheres, also by drinking contaminated water; the carriers of T. solium, moreover, infect themselves still more frequently through uncleanliness in defæcation, the privies in public localities and many private houses affording striking testimony of this. The minute oncospheres can thus easily reach the fingers and thence the mouth (as in twirling the moustache, biting the nail). More rarely a third manner of transmission or internal auto-infection may possibly take place, as when, in the act of vomiting, mature proglottids near the stomach are drawn into it; the oncospheres or segments there retained are then in the same position as if they had been introduced through the mouth.

On account of these dangers of internal or external auto-infection, it is therefore the duty of the medical attendant, after recognizing the presence of tapeworms, to expel them,[290] and in doing so to employ every possible means to prevent vomiting setting in; it is, however, equally important to take the necessary steps to destroy the parasites evacuated. It may be incidentally mentioned that in using certain remedies the scolex not rarely remains in the intestine; the cure in such cases has not been accomplished, as the scolex again produces new proglottids, and after about eleven weeks the first formed ones are again mature and appear in the fæces.

[290] The diagnosis as a rule is not difficult; the patients themselves frequently observe the pumpkin seed-like segments in the fæces. But in such cases the diagnosis must still be confirmed. In other cases the discovery of the oncospheres in their embryonal shells (embryophores), which cannot be confounded with the other constituents of the fæces, gives complete certainty, although the differential diagnosis between T. solium and T. saginata is hardly possible from the embryophores; but, if evacuated segments are placed between two slides and lightly pressed, the species is easily recognizable by the shape of the uterus (cf. figs. 239 and 241).

Amongst the cysticerci also many malformations appear; thus absence of the rostellum and the hooks, or double formation with six suckers, or abnormalities of growth on account of the surroundings, which have had a special name given to them, viz., Cysticercus racemosus, Zenk. (= C. botryoides, Hell.; C. multilocularis, Kchnmstr.); these forms are more especially found at the base of the brain, are irregularly ramified and often without the head.

A certain interest is attached to those forms that have led to the establishment of a distinct species:--

*Cysticercus acanthotrias*, Weinld., 1858.

In making the autopsy of a white Virginian woman who had died of phthisis, a cysticercus was found in the dura mater, and eleven or twelve specimens in the muscles and subcutaneous tissue. Weinland and Leuckart, who examined the specimens, found that they resembled Cysticercus cellulosæ in form and size, but that they carried on the rostellum a triple crown, each consisting of fourteen to sixteen hooks, which differed from the hooks of C. cellulosæ or of Tænia solium by the greater length of the posterior root process and the more slender form of the hooks; the large hooks measured 0·153 to 0·196 mm., the medium-sized hooks, 0·114 to 0·14 mm., and the small ones 0·063 to 0·07 mm.

On account of these differences a distinct species of cysticercus was established, and this naturally presupposed a corresponding species of Tænia (T. acanthotrias, Lkt.); this could be done with justice so long as the case remained isolated, i.e., in America, as there was the possibility of the corresponding Tænia being found. In this respect, however, the position has changed; Delore first described a cysticercus the size of a nut from the biceps muscle of the arm of a silk-worker in Lyons; according to Bertolis this specimen possessed hooks of three different sizes, the dimensions of which corresponded with the figures given by Weinland and Leuckart; the correctness of the diagnosis could hardly be doubted, as Bertolis was known to be a very exact observer. A second case has become known through Cobbold, who regards a specimen of a cysticercus in Dallinger’s collection as likewise belonging to Cysticercus acanthotrias; this specimen also came from a man’s brain; finally a third case, also from France, has been published by Redon. This author, amongst numerous C. cellulosæ of a man, found one that had forty-one hooks in three rows, and he was the first to express the opinion that C. acanthotrias does not represent a distinct species, but is only an abnormality of C. cellulosæ. This view was also taken by Blanchard and Railliet, and is probably correct, as the discovery of the large corresponding Tænia furnished with three rows of hooks is not to be expected in European beasts of prey, and in Redon’s case C. acanthotrias as well as C. cellulosæ occurred simultaneously.

The duration of life of C. cellulosæ in man is very long; cysticerci of the eye have been known to persist for twenty years, and in cysticercus of the brain ten to nineteen years may elapse from the first appearance of cerebral symptoms until death. Dead cysticerci may shrivel up or become calcified, perhaps also undergo fatty degeneration and then absorption. Finally, it may be mentioned that if particular proof is required that C. cellulosæ of man belongs to the cycle of development of the Tænia solium, such proof has been furnished by Redon.

NOTE.--Tænia tenella, mentioned on p. 332, was ascribed by Cobbold to cysticerci of the muscular system of sheep. It has, however, been demonstrated that these cysticerci belong to the cycle of development of Tænia marginata (dog) (Cysticercus tenuicollis, from the omentum of sheep); but as already stated C. cellulosæ also occurs in sheep. Chatin himself swallowed the cysticercus, which Cobbold termed C. ovis, without causing a Tænia to develop in his intestine. Müller also vainly sought to induce infection with C. tenuicollis in his own person. On the other hand, the feeding of a dog with Cysticercus ovis resulted in the production of Tænia marginata.

*Tænia bremneri*, Stephens, 1908.

Characterized by the large size of the gravid segments. The largest was 32 by 9 mm. Smallest 21 by 6 mm. Average 28·6 by 8·5 mm. Mode 21 by 6 mm. Uterine branches twenty-two to twenty-four in number. Calcareous bodies numerous, 15·2 µ in diameter. Eggs maximum 45·6 µ by 41·8 µ. Smallest 34·2 µ by 30·4 µ. Mode 38 µ by 30·4 µ.

*Tænia marginata*, Batsch, 1786.

Syn.: T. e. Cysticerco tenuicolli, Küchenmeister, 1853.

This species, which in structure resembles Tænia solium, lives in the intestine of the dog and the wolf. It attains 1·5 to 4 m. in length, possesses a double crown of thirty to forty hooks, on an average thirty-six to thirty-eight hooks, and in its larval stage (Cysticercus tenuicollis) lives in the peritoneal cavity of ruminants and the pig, occasionally in the monkey and squirrel.

It is included in this work because, according to one statement, C. tenuicollis is supposed to have been observed in man in North America; but the case is not quite certain, as the number of hooks was less than in C. tenuicollis and coincided with C. cellulosæ, although the size of the cysticercus appeared to point to C. tenuicollis. A yet earlier statement of Eschricht, that Cysticercus tenuicollis had been observed in Iceland in the liver of a man, is undoubtedly due to an error.

*Tænia serrata*, Goeze, 1782.

This parasite attains a length of from 0·5 to 2 m., possesses a double crown of thirty-four to forty-eight (mostly forty) hooks. It lives exclusively in the intestine of the dog, the corresponding cysticercus (Cysticercus pisiformis) living in the mesentery of the hare and rabbit. We mention this species with all reserve amongst the parasites of man, because Vital states that he has observed it twice in Constantine (Algeria) in human beings. The data, however, are not sufficient to characterize the species. It is highly probable that they relate to Tænia solium. Galli-Valerio even swallowed five specimens of Cysticercus pisiformis, but without result.

*Tænia crassicollis*, Rud., 1810.

I only mention this species from the intestine of the domestic cat because Krabbe regards its occurrence in man as possible. It attains a length of 60 cm. and is armed; its cysticercus (Cysticercus fasciolaris) lives in the liver of mice and rats. In Jutland, according to Krabbe, chopped-up mice (spread on bread) are eaten raw, being a national remedy for retention of urine, and this custom affords the possibility of the introduction of C. fasciolaris into the intestine of man (Nord. med. Arkiv, 1880, xii).

*Tænia saginata*, Goeze, 1782.

Syn.: Tænia solium, L., 1767 (pro parte); Tænia cucurbitina, Pallas, 1781 (p.p.); Tænia inermis, Brera, 1802. Moquin-Tandon, 1860; Tænia dentata, Nicolai, 1830; Tænia lata, Pruner, 1847; Bothriocephalis tropicus, Schmidtmuller, 1847; Tænia mediocanellata, Küchenmeister, 1855; Tænia zittavensis, Küchenmeister, 1855; Tænia tropica, Moquin-Tandon, 1860; Tænia (Cystotænia) mediocanellata, Leuckart, 1863.

The length of the entire tapeworm averages 4 to 8 to 10 m. and more, even up to 36 m. According to Bérenger-Feraud it attains a length of 74 m. (?) The head is cubical in shape, 1·5 to 2 mm. in diameter; the suckers are hemispherical (0·8 mm.) and are frequently pigmented; there is a sucker-like organ in place of the rostellum, and this also is frequently pigmented. The neck is moderately long and about half the breadth of the head; the proglottids, the number of which averages more than 1,000, gradually increase in size; the mature detached segments are shaped exactly like pumpkin-seeds, and are about 16 to 20 mm. in length and 4 to 7 mm. in breadth. The genital pores alternate irregularly and are situated somewhat behind the middle of the lateral margin. There are twenty to thirty-five lateral branches at each side of the median trunk of the uterus, and these again ramify. The eggs are more or less globular, the egg-shell frequently remains intact and carries one or two filaments; the embryonal shell (embryophore) is thick, radially striated, is transparent and oval; it is 30 µ to 40 µ in length, and 20 µ to 30 µ in breadth. Several segments simultaneously are usually passed spontaneously with defæcation.

Malformations are not uncommon, and resemble those of Tænia solium; a triangular form has been termed T. capensis by Küchenmeister, and T. lophosoma by Cobbold, names that naturally possess as little value as does the term T. fenestrata for fenestrated specimens. Moreover, T. solium, var. abietina, Weinld., 1858, which was evacuated by an Indian, was probably a T. saginata with somewhat close uterine branches. It is regarded by Stiles and Goldberger as a doubtful subspecies.

T. saginata in its adult condition lives exclusively in the intestinal canal of man.[291] The corresponding cysticercus is Cysticercus bovis, and is found almost exclusively in the ox; it is small, 7·5 to 9 mm. in length and 5·5 mm. in breadth, may easily escape notice, and requires from three to six months for its development. Numerous experiments have confirmed the connection of Cysticercus bovis with Tænia saginata; indeed, the cysticercus was only discovered by feeding experiments after attention had been called to the ox as the probable intermediary host of this Tænia.

[291] Abnormal migrations of this species have also been known. Compare, amongst others, Stieda, A., “Durchbohr. d. Duod. u. d. Pancreas durch eine Tænia,” Centralbl. f. Bakt., Path. und Infektionsk., 1900, xxviii (1), p. 430.

Medical men observed that weakly children who were ordered to eat raw scraped beef to strengthen them contracted T. saginata. It was found, moreover, that Jews, who are prohibited from eating pork from religious motives, suffered especially from T. saginata; when T. solium was found to occur in a Jew he often confessed to having eaten pork; and finally it was found that certain nations--for instance, the Abyssinians--frequently harbour T. saginata, and only eat beef--raw by preference.

These observations led Leuckart, in 1861, to feed young calves with the proglottids of T. saginata in order to discover the corresponding cysticercus, which was then not known. This experiment was successful. Similar experiments, with similar results, were then conducted by Mosler (1863), Cobbold and Simonds (1864 and 1872), Röll (1865), Gerlach (1870), Zürn (1872), Saint Cyr, Jolicœur (1873), Masse and Pourquier (1876), and Perroncito, in 1876. The attempts to infect goats, sheep, dogs, pigs, rabbits and monkeys were unsuccessful. Only Zenker and Heller were able to infect kids, and Heller infected one sheep, but these are exceptions.

Artificial infections of human beings with Cysticercus bovis to obtain the tapeworm were less numerous, and indeed quite superfluous, yet this was also done by Oliver (1869) in India, and Perroncito (1877) in Italy. The experiments of the latter prove that the extracted cysticerci of the ox certainly perish in water at 47° to 48° C.

It is a remarkable circumstance that, at least as regards Central Europe, C. bovis in the ox, after natural infection, was so seldom found that almost every case was published as a rarity; whereas the Tænia is very frequent in man. The reason for this is that in Germany cattle are not severely infected, and that the small, easily dried-up cysticerci easily escape notice in the large body of the host. Hertwig, the late director of the town cattle market in Berlin, in 1888, pointed out that the cysticercus of the ox is found chiefly in the musculi pterygoide externi and interni, and since that time a far greater number of infected oxen have been found in Berlin.

---------+----------------+----------+------------ Year | Number of oxen | Infected | Proportion | slaughtered | | ---------+----------------+----------+------------ 1888–89 | 141,814 | 113 | 1 : 1,255 1889–90 | 154,218 | 390 | 1 : 395 1890–91 | 124,593 | 263 | 1 : 474 1891–92 | 136,368 | 252 | 1 : 541 1892–93 | 142,874 | 214 | 1 : 672 ---------+----------------+----------+------------

Since 1892 an increase has taken place in the number of oxen infected with cysticercus, but this is probably attributable to the more general and searching examinations. In the slaughter-houses of Prussia the number of infected beasts was as follows:--

1892 567 1893 686 1894 748 1895 1,143 1896 1,981 1897 2,629

The condition was most frequent in Neisse (3·2 to 4 per cent.), Eisenach (1·91 per cent.), Ohlau (1·57 per cent.), Oels i. Schles. (1 per cent.), Marienwerder (0·34 to 1·2 per cent.). The flesh of oxen only slightly infected (containing not more than ten living cysticerci) is sold in pieces of not more than 5 lb. to consumers after having been rendered innocuous by cooking, or by pickling for twenty-one days in 25 per cent. salt brine, or hanging for twenty-one days in suitable refrigerators; oxen in which only one cysticercus is found are allowed free commerce, and those strongly infected (i.e., containing more than ten living cysticerci) may only be used for industrial purposes.

It is a striking fact that more bulls than cows are infected (according to Reissmann, in Berlin, from 1895 to 1902, 0·446 per cent. bulls, 0·439 per cent. oxen, and 0·262 per cent. cows), the explanation of which, according to Ostertag, is that most oxen are killed when young, when also infection most readily takes place, and, further, that the larva later on in life can be completely atrophied.

The cysticercus of the ox has hitherto been found in man on very rare occasions. Arndt (Zeitschr. f. Psychiat., xxiv) mentions a case in the brain, Heller in the eye, and Nabiers and Dubreith also in the brain (Journ. méd. Bordeaux, 1889–1890, p. 209); but the diagnoses are not quite certain, as absence of hooks occasionally occurs in Cysticercus cellulosæ.

Tænia saginata is the most frequent tapeworm of man (with the exception of Dibothriocephalus latus in a few districts), and the parasite is widely distributed over the surface of the globe; it has been known in the East for ages, so far as data are available; it is frequent in Africa, America, and Europe. Its frequency has perceptibly increased during the last few years, but a decrease should soon take place in consequence of the extent and improvement of the official inspection of meat.

The following table shows the relative frequency of the Cestodes of man:--

----------------+---------+----------+----------+-------+------+-------+-------- | |Number of | _T. | _T. |_Dibr.|Dipyl.|Undeter- Author | Year | cases |saginata |solium_|latus_|canin._| mined ----------------+---------+----------+----------+-------+------+-------+-------- Parona (Milan) | 1899 | 150 | 121 | 11 | 4 | -- | 14 Parona (Italy) | 1868–99 | 513 | 397 | 71 | 26 | -- | 19 Krabbe (Denmark)| 1869 | 100 | 37 | 53 | 9 | 1 | -- " " | 1869–86 | 200 | 153 | 24 | 16 | 8 | -- " " | 1887–95 | 100 | 89 | -- | 5 | 6 | -- " " |1896–1904| 50 | 41 | 1 | 5 | 3 | -- Blanchard | 1895 | ? | 1,000 | 21 | -- | -- | -- (Paris) | | | | | | | Stiles | 1895 |{more than|more than}| -- | 3 | -- | -- (United States)| |{ 300 | 300 }| | | | Schoch | 1869 | 19 | 16 | 1 | 2 | -- | -- (Switzerland) | | | | | | | Zaeslein | 1881 | ? | 180 | 19 | ? | | (Switzerland) | | | | | | -- | -- Kessler | 1888 | ? | 22 | 16 | 47 | -- | -- (Petrograd) | | | | | | | Mosler | 1894 | 181 | 112 | 64 | 5 | -- | -- (Greifswald) | | | | | | | Bollinger | 1885 | 25 | 16 | 1 | 8 | -- | -- (Munich) | | | | | | | Vierordt | 1885 | 121 | 113 | 8 | -- | -- | -- (Tübingen) | | | | | | | Mangold | 1885–94 | 128 | 120 | 6 | 8 | -- | -- (Tübingen) | | | | | | | ----------------+---------+----------+----------+-------+------+-------+--------

*Tænia africana*, v. Linst., 1900.

This worm measures over 1·3 m. in length. The segments are all broader than they are long. The scolex is unarmed and is provided with an apical sucker (0·16 mm.). The parasite measures 1·38 mm. in breadth, 1·03 mm. in width; the suckers measure 0·63 mm. in diameter. The neck is very short and somewhat broader than the scolex; number of segments about 600; the hindmost segments measure 7 mm. in length and 12 to 15 mm. in breadth. The genital pores alternate irregularly in the middle of the lateral margin; the testes are very numerous and occupy the entire medullary layer; the vas deferens is much convoluted; the cirrus pouch is pyriform and thick walled; the cirrus and vagina are beset with bristles directed outwards; the receptaculum seminis is fusiform; the ovary is large and double, and consists of radially placed club-shaped tubes that do not anastomose and do not branch; the vitellarium is at the posterior border of the proglottids, the round shell gland in front of it; the uterus consists of a median trunk and fifteen to twenty-four non-ramified lateral branches on each side; the embryonal shell is thick and has radial stripes--it may be round (31·2 µ to 33·8 µ) or oval (39 µ, by 33·8 µ); the spines of the oncospheres measure 7 µ to 8 µ in length (fig. 197).

At present only two specimens are known; they came from a black soldier from the vicinity of Lake Nyasa. The cysticercus is unknown; perhaps it lives in the zebu, the flesh of which the Askaris are in the habit of devouring uncooked.

*Tænia confusa*, Ward, 1896.

Length 8·5 m., breadth about 5 mm. The scolex is unknown; there is no neck; number of proglottids 700 to 800, always longer than they are broad; the hindmost measure 35 mm. in length, 4 to 5 mm. in breadth; the genital pores alternate irregularly behind the middle of the lateral margin; testicles numerous; vas deferens not much coiled; the cirrus pouch thick walled, elongated and club-shaped, with globular vesicula seminalis; the cirrus is beset with little hairs; the receptaculum seminis is globular; ovary small, double; each half is bean-shaped; vitellarium narrow, triangular; shell gland globular; uterus with median trunk and fourteen to eighteen short ramified lateral branches on either side. The embryophores are oval (39 µ by 30 µ), thick and radially striated.

Of this species only two specimens have been recorded; they occurred in human beings and were sent at different times to the first describer of them by a doctor in Lincoln (Nebr.). Perhaps Tænia solium, var. abietina, Weinld., which was found in a Chipeway Indian, is of the same species in spite of the shorter segments.

*Tænia echinococcus*, v. Sieb., 1853.

Syn.: Tænia nana, v. Ben., 1861 (nec v. Sieb., 1853); Echinococcifer echinococcus, Weinld., 1861.

Tænia echinococcus measures 2·5 to 5 or 6 mm. in length; the head is 0·3 mm. in breadth, and has a double row of twenty-eight to fifty hooklets (on an average thirty-six to thirty-eight) on the rostellum.

The size and form of these hooklets vary (the larger ones are 0·040 to 0·045 mm. in length, the smaller ones are 0·030 to 0·038 mm. in length). The suckers measure 0·13 mm. in diameter; the neck is short; there are only three or four segments, the posterior segment being about 2 mm. in length and 0·5 mm. in breadth. The genital pores alternate; there are forty to fifty testicles; the vas deferens is spirally coiled; the cirrus pouch is pyriform. The ovary is horseshoe-shaped with the concavity directed backwards; the vitellarium double, each half almost bean-shaped, at right angles to the plane of the segment; the shell gland is round. The median trunk of the uterus is dilated when filled with eggs and (instead of lateral branches) has lateral diverticula. It is not unusual for the eggs to form local heaps. The embryonal shell (embryophore) is moderately thin, with radial striæ, almost globular, 30 µ to 36 µ in diameter.

When mature this parasite lives in the small intestine of the domestic dog, the jackal, and the wolf, and apparently also in Felis concolor, and is usually present in great numbers; it can also be transmitted experimentally to the domestic cat, one successful result out of seven (Dévé).[292] The larval stage (Echinococcus polymorphus) lives in various organs--chiefly in the liver and lungs--of numerous species of mammals (twenty-seven), especially in sheep, ox and pig, and it is even not uncommon in man, though the Tænia itself has never been found in a human being; accordingly man can only acquire the echinococcus by ingesting the eggs of the “dog worm.” The dogs disseminate the eggs of Tænia echinococcus wherever they go, or carry them to their mouths and coats by biting up the evacuated segments, and are thus able to transmit them directly to human beings (by licking them or making use of the same crockery, etc.). In other cases the oncospheres, enclosed in the embryophores, must withstand desiccation for a time and then (as when the dogs are “kissed” or otherwise caressed) are transmitted into or on to man. As echinococcus disease in man is always very dangerous, it would be a matter of general interest to prevent dogs being infected by destroying the echinococci,[293] and all measures would be justifiable which would diminish the superfluous number of house-dogs (for instance, high taxes); measures should also be adopted to limit the association of men with dogs, particularly in such frequented places as restaurants, railway carriages and tram-cars.

[292] In Iceland 28 per cent. of the dogs are infected with this Tænia, in Lyons 7·1 per cent., in Zurich 3·9 per cent., in Berlin 1 per cent., and in Copenhagen 0·4 per cent. In Australia even 40 to 50 per cent. of the dogs are affected. It is, however, a question whether, in addition to Tænia echinococcus, a second analogous form is not involved, as the form from Canis dingo attains a length of 10 to 30 mm.

[293] Mosler, F., “Ueb. Mittel z. Bekampfg. endem. vork. Echinococcuskrank.,” Deutsch. med. Zeit., 1889, No. 72.

Echinococcus is very common in slaughtered animals; in Germany, however, the figures in the reports of the abattoirs present an erroneous view in so far as, besides the total number of animals slaughtered, only the numbers of those organs (liver and lungs) are published that were so severely infected with echinococci that, even when the parasites were “shelled” out, the flesh could not be placed upon the market and was therefore “condemned.”

In Berlin the following animals were slaughtered:--

-------+---------+---------+---------+---------+---------+--------- Year | 1889–90 | 1890–91 | 1891–92 | 1892–93 | 1896–97 | 1902 -------+---------+---------+---------+---------+---------+--------- Oxen | 154,218 | 124,593 | 136,368 | 142,874 | 146,612 | 153,748 Sheep | 430,362 | 371,943 | 367,933 | 355,949 | 395,769 | 434,155 Pigs | 442,115 | 472,859 | 530,551 | 518,073 | 694,170 | 778,538 -------+---------+---------+---------+---------+---------+---------

During the same years the following were condemned in consequence of being infected with echinococci:--

-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+----- |Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver -----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+----- Oxen |7,266|2,418|5,792|1,938|4,497|1,721|2,563| 739|3,284|1,156| 2,507| 791 Sheep|5,479|2,742|4,595|2,059|4,435|1,669|3,331|1,161|4,561|1,939|11,138|4,437 Pigs |6,523|5,078|5,083|3,735|6,037|4,374|6,785|4,312|7,888|5,398| 9,544|9,233 -----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----

Nevertheless there are statistics that give the total number of animals infected with echinococcus:--

--------+-------------+--------------+--------------+-------------- Author | Place | Oxen | Sheep | Pigs --------+-------------+--------------+--------------+-------------- Längrich|Rostock i. M.|26·2 per cent.|37·0 per cent.| 5·4 per cent. Olt |Stettin | 7·1 " |25·8 " | 7·3 " Steuding|Gotha |24·6 " |35·4 " |21·4 " Prettner|Prague |23·2 " | 5·5 " | ? --------+-------------+--------------+--------------+--------------

In Güstrow, in Mecklenburg, half of the animals slaughtered are said to be infected with echinococcus; in Wismar 25 per cent. of the oxen, 15 per cent. of the sheep and 5 per cent. of the pigs are infected; according to Mayer, in Leipzig, 3·79 per cent. native pigs, 24·47 per cent. Hungarian pigs, and 13·09 per cent. of sheep were infected with echinococcus; at the same time it was stated that in regard to the native pigs the liver was more frequently affected than the lungs (3·81 per cent. as compared with 0·26 per cent.); in sheep the lungs were more frequently infected (12·71 per cent. to 3·73 per cent.), whereas in the Hungarian pigs both organs were almost equally infected (14·78 per cent. to 12·03 per cent.).

The data of Lichtenheld, in Leipzig, give the frequency with which various organs were affected, as shown in the following table:--

-----------+---------+-------------------+---------+--------- | Cattle | Pigs | Sheep | Horses -----------+---------+-------------------+---------+--------- | | ♂ | ♀ | | |per cent.|per cent.|per cent.|per cent.|per cent. Lungs | 69·3 | 16·2 | 21·4 | 52·2 | 5·5 Liver | 27·0 | 74·2 | 72·0 | 44·9 | 94·5 Spleen | 2·2 | 3·2 | 2·7 | 2·9 | -- Heart | 0·75 | 3·2 | 1·3 | -- | -- Kidneys | 0·75 | 3·2 | 1·3 | -- | -- Sub- | | | | | peritoneal| | | | | tissue | -- | -- | 1·3 | -- | -- -----------+---------+---------+---------+---------+---------

STRUCTURE AND DEVELOPMENT OF ECHINOCOCCUS (HYDATID).

An echinococcus is a spherical or roundish bladder full of a watery liquid, which originates by liquefaction of the oncosphere, and in man may attain the size of a child’s head, but remains smaller in cattle (the size of an orange or apple). The thin wall of the bladder is composed of an external laminated cuticle (ectocyst) and an internal germinal or parenchymatous layer (endocyst). The latter again exhibits two layers: an outer layer of small cells that are less sharply defined, and an inner layer of larger cells. It contains, in addition, calcareous corpuscles, muscular fibres and excretory vessels. It is rich in glycogen.

The development in cattle often remains stationary at the bladder stage, and they are then called “acephalocysts,” or Echinococcus cysticus sterilis. According to Lichtenheld, sterile cysts occur in 80 per cent. of cases in cattle, in 20 per cent. in pigs, and in 7·5 per cent. in sheep. In other cases large numbers of small, hollow BROOD CAPSULES are formed in the germ layer, but are not arranged in any particular order. The order of the layers is just the reverse in them to what it is in the parent cyst, that is to say, they have inside a thin non-laminated cuticle and the parenchymatous layer on their external surface. These, theoretically at least, may be regarded as invaginations of the bladder wall giving rise to a cavity with the cuticle internal and the parenchymatous layer external. If we suppose the orifice to close, we should then get an isolated cavity with cuticle internal and parenchymatous layer external, as in the brood capsule (fig. 252). If we next suppose an evagination of the wall of the brood capsule to occur at one point we should get a hollow process lined with cuticle; at the bottom of this we get the scolex and hooklets formed, and a little higher up the tube the suckers (fig. 252, 4). If this hollow scolex is now pictured as being invaginated we get a hollow scolex covered with cuticle and lined by a parenchymatous layer projecting into the cavity of the brood capsule. The two sides of this hollow scolex now fuse and we get a solid scolex projecting into the cavity. Finally, if we imagine once more the rostellum and suckers invaginated into the posterior part of the scolex we get the condition as frequently found in the brood capsules, i.e., a scolex covered with cuticle projecting into the cavity, with the rostellum and suckers invaginated into the posterior portion of the scolex (fig. 252A, 7).

A large hydatid may contain many thousands of brood capsules. Each brood capsule is about as big as a pin’s head, and may contain ten to thirty or more scolices. The delicate wall of the brood capsules may rupture, so that the scolices are now free in the mother cyst. These free scolices and also free brood capsules constitute what is known as “hydatid sand,” which settles at the bottom of a glass when hydatid fluid is poured into it. This form occurs chiefly in domesticated animals and is termed E. veterinorum, Rud., or E. cysticus fertilis.

In man, and only rarely in cattle, the mother cyst first forms “daughter cysts” (E. hominis, Rud. [fig. 255]), which, though smaller than the “mother cyst,” resemble it in the structure of their walls; thus they are covered externally by a laminated cuticle and internally by the parenchymatous layer. They originate:

(1) Between the laminæ of the cuticle of the mother cyst from small, detached portions of the parenchymatous layer; during their growth they bulge inwardly or outwardly and may separate themselves entirely from their parent cyst. In the latter case they lie between the mother cyst and the capsule of connective tissue formed by the host (E. granulosus or E. hydatidosus exogenus); when growing inwardly they reach the interior of the mother cyst (E. hydatidosus endogenus). Their number is very variable and does not depend on the size of the mother cyst. They are as big as, or bigger than, gooseberries.

(2) According to some authors, endogenous daughter cysts arise also from a metamorphosis of scolices that have separated off from the brood capsule. This takes place in the following way: Fluid accumulates in the interior of the scolex, so that eventually nothing remains except a sac consisting of cuticle lined by parenchyma. The cuticle gradually thickens and several layers form (fig. 257).

(3) Transformation of Brood Capsules into Daughter Cysts.--This is also held to be possible by various observers. New epithelial layers are deposited between the cuticle which lines the brood capsule and the outer parenchymatous layer. This parenchymatous layer gradually disappears and a new parenchymatous layer forms in the interior from the parenchyma of the scolex or scolices. Although it appears strange that a completely formed scolex with specifically differentiated tissues and organs should retrogress to more primitively organized matter, and again become a proliferating bladder, yet we can hardly doubt that the older observations, regarding such a vesicular metamorphosis, of Bremser (1819), v. Siebold (1837), Naunyn (1862), Rasmusser (1866), Leuckart (1881), Alexinsky (1898), Riemann (1899), Dévé (1901), and Perroncito (1902) are correct.

(4) Further, a fourth method of formation of daughter cysts is described by Naunyn as occurring in sterile hydatids, i.e., those containing no brood capsules. In this case a portion of the mother wall of the hydatid gets constricted off.

It has also been established that not only daughter cysts transplanted into animals develop further (Lebedeff, Andrejew, Stadnitzky, Alexinsky, Riemann), but that this also holds good if only hydatid scolices from man or animals are transplanted into animals (rabbits). They develop into echinococci and can then give rise to brood capsules and scolices. As Dévé further established, hydatid scolices are not capable of developing in guinea-pigs, while corresponding experiments with rabbits are in the large majority of cases successful where the scolices are introduced subcutaneously or into the pleural or peritoneal cavities. It is only in the case of daughter cysts that further growth is obtained in the case of guinea-pigs. Finally it appears, as has been already stated, that brood capsules can transform themselves into daughter cysts, but according to Dévé only within the mother cyst, not after transplantation. Daughter cysts that have been formed in the mother cyst of man and animals behave themselves just as the mother cyst does, i.e., they can remain sterile, or give rise to brood capsules and scolices, or even again to fresh cysts--granddaughter cysts. The mother cyst can also die, so that the daughter cysts then lie in the cavity of the connective tissue capsule. The number of the daughter cysts in either case may attain several thousands.

The echinococcus fluid, which originally is formed from the blood of the host, is light yellow, with a neutral or slightly acid reaction; its specific gravity averages 1009 to 1015. It contains about 1·5 per cent. of inorganic salts, half of which is common salt; in addition (besides water) it contains sugar, inosite, leucine, tyrosin, succinic acid (associated with lime or soda) and albumens which are not coagulated by heat; occasionally also the fluid has been found to contain hæmatoidin and uric acid salts (in echinococcus of the kidneys), which doubtless demonstrates that the echinococcus liquid originates from the host. It has been generally assumed that echinococcus fluid contains a toxic substance the escape of which into the body cavity (at operation or by bursting of a hydatid cyst) produces more or less severe symptoms (fever, peritonitis, urticaria), so much so that one speaks of hydatid intoxication. The investigations of Kobert, Joest, etc., have, however, shown the harmlessness of fresh undecomposed hydatid and cysticercus fluid for rabbits, mice and guinea-pigs, whether inoculated intraperitoneally, subcutaneously or intravenously. Contrary data or clinical experience must accordingly depend on other factors.

According to the researches of Leuckart, the growth of the echinococcus is very slow; four weeks after infection the average size is only 0·25 to 0·35 mm., at the age of eight weeks it is 1 to 2·5 mm., and at this period the formation of the central cavity commences; at the age of five months, and with a size of 15 to 20 mm., the first brood capsules with scolices are formed. The consequence of this gradual increase of size is that the organ attacked can maintain its functions by vicarious hypertrophy, and that many echinococci induce no special symptoms and cannot even be diagnosed, the latter circumstance being due to their hidden position.

The echinococcus cannot be said to be scarce in man, as is shown by the following table for Central Europe:--

--------------------+-------+--------------+------------+---------- Place | | No. of |No. of cases|Percentage |Period |post-mortems| of echino. | --------------------+-------+--------------+------------+---------- Rostock |1861–83| 1,026 | 25 | 2·43 Greifswald |1862–93| 3,429 | 51 | 1·48 Jena |1866–87| 4,998 | 42 | 0·84 Breslau |1866–76| 5,128 | 39 | 0·761 Berlin |1859–68| 4,770 | 33 | 0·69 Würzburg | -- | 2,280 | 11 | 0·48 Göttingen | -- | 639 | 3 | 0·469 Dresden |1852–62| 1,939 | 7 | 0·36 Münich |1854–87| 14,183 | 35 | 0·25 Vienna | 1860 | 1,229 | 3 | 0·24 Prague | -- | 1,287 | 3 | 0·23 Kiel |1872–87| 3,581 | 7 | 0·19 Zürich, Basle, Berne| -- | 7,982 | 11 | 0·13 Erlangen |1862–73| 1,755 | 2 | 0·11 --------------------+-------+--------------+------------+----------

These, however, are only cases that have become known by post-mortem; in addition, there are cases that have been treated medically, of which there are a few statements, at all events relating to the principal districts of Germany. According to Madelung, one case of echinococcus occurs in every 1,056 inhabitants in the town of Rostock, in the district of Rostock one to every 1,283, in Schwerin one to every 5,887, and in Ludwigsort one to every 23,685; according to Peiper, in Upper Pomerania one case occurs to every 3,336, in the district of Greifswald one to every 1,535 inhabitants. The northern districts of Pomerania are more affected than the southern ones.

Accordingly, echinococcus is also considerably more frequent in cattle in Pomerania. On an average in Germany 10·39 per cent. oxen, 9·83 per cent. sheep, and 6·47 per cent. pigs are infected, whereas in Upper Pomerania 37·73 per cent. oxen, 27·1 per cent. sheep, and 12·8 per cent. pigs are infected; in Greifswald, indeed, 64·58 per cent. oxen, 51·02 per cent. sheep, but only 4·93 per cent. pigs are infected. In accordance with these figures Tænia echinococcus must be frequent in dogs in Pomerania, especially in Upper Pomerania; on the other hand, the conjecture that the frequency of echinococcus in Mecklenburg is explained by the occurrence of Tænia echinococcus in foxes has not been confirmed, as the fox does not harbour this worm in Mecklenburg.

Beyond the European continent, echinococcus is frequent in the inhabitants of Iceland, Argentine, Paraguay and Australia. In Iceland, according to Finsen, 1 in every 43 inhabitants is affected with echinococcus; according to Jonassen the proportion is 1 to 63; this is due to the habits of the people of Iceland or, in fact, to the frequency of Tænia echinococcus in dogs, and the prevalence of the hydatid in cattle. In certain districts of Australia it is just as frequent. In Cape Colony, Egypt and Algeria echinococcus is not rare, but it is scarce in America and in Asia, with the exception of the nomadic tribes of Lake Baikal.

Echinococcus attacks persons of every age, though it is rare in children up to 10 years of age and in old people. It occurs most frequently between the ages of 21 and 40 years. According to all statistics it preponderates in women (about two-thirds of the cases). The liver is its favourite seat (57·1 per cent. of the cases); next in order come the lungs (8 per cent.), kidneys (6 per cent.), cranial cavity, genitalia, organs of circulation, spleen (3·8 per cent.), etc. As a rule one organ only is invaded; multiple occurrence may originate from one infection, or eventually from a later infection (?), or it may come to pass that from some cause (through the spontaneous rupture of an echinococcus, or the rupture of one caused by an injury or surgical operation) daughter cysts, brood capsules or scolices escape into the abdominal cavity,[294] where they settle or become transformed and go on growing. In the distribution of this secondary echinococcus the great powers of motility of the free scolices must be taken into account (Sabrazès, Muratet, and Husnot).

[294] In such cases the toxic effects of the echinococcus fluid usually--if not always--manifest themselves. Such effects are manifested by severe symptoms of poisoning being set up, by urticaria, peritonitis, and ascites, and not infrequently they cause a fatal termination.

Human echinococci may also die at various stages of development, become caseous or calcified, or may be absorbed, the cause for this being either disease of the hydatid itself or inflammation of its connective tissue capsule; the discovery of the laminated cuticle, which has great powers of resistance, or the finding of the hooklets of the scolices is sufficient to form a conclusion as to the nature of such formations.

Siebold (1853) was the first to rear Tænia echinococcus in the dog by feeding it with the echinococcus of cattle and especially of sheep. Küchenmeister, van Beneden, Leuckart, Railliet and others obtained similar results, and Thomas, Naunyn, Krabbe and Finsen succeeded in rearing T. echinococcus in dogs from the bladder worms of human beings; these grow comparatively slowly (one to three months[295]) and only during the process of growth develop their hooklets in their definite form (fig. 258). It lies in the nature of things that dogs, whether experimentally or naturally infected, almost always harbour T. echinococcus in large quantities. That cats exceptionally harbour these worms has been already mentioned (Dévé). Finally, Leuckart infected young pigs by feeding them with mature segments.

[295] According to Perroncito the scolices had not formed proglottids nine days after feeding, but the latter were present twenty-four days after feeding, although the formation of eggs had not begun.

*Echinococcus multilocularis* (alveolar colloid).

In addition to the form of echinococcus already described, and which is also frequently termed Echinococcus unilocularis, there is a second form which occurs in man as well as in animals, and which is termed E. multilocularis, s. alveolaris (alveolar colloid).

It was originally regarded as a tumour; its animal nature was first established by Zeller and R. Virchow. The parasite, which varies in size from that of a fist to a child’s head, presents a collection of numerous cysts, measuring between 0·1 and 3 to 4 mm. to 5 mm. in diameter, which are embedded at first in a soft, connective tissue stroma; the cut surface has therefore a honeycomb appearance. The cysts are surrounded by a pellucid and laminated cuticle, and each according to its size encloses either a small-celled tissue or a cavity lined by a parenchymatous layer; the fluid contained in such a cavity may be transparent, or is rendered opaque by globules of fat, bile-pigment, hæmatoidin and fat crystals. According to some authors all or most of these cysts intercommunicate; others state that this is the case at least as regards the cuticle. The scolices are by no means found in all the cysts, and when present only a few, rarely half, of the cysts contain scolices (one or more); it is supposed that at least some of these scolices are formed in brood capsules, and that the former are capable of undergoing a cystic metamorphosis.

One circumstance is peculiar to the multilocular echinococcus of man, namely, the disintegration that sets in at certain stages; in the centre of the parasite a cavity forms that frequently becomes very large and is filled with a purulent or brownish or brownish-green viscid fluid; in this fluid one finds shreds of the wall of the cavity, calcareous bodies, echinococcus cysts, also scolices and hooklets, as well as fat globules and crystals of hæmatoidin, margarine and cholesterin and concretions of lime. Such ulcerative processes, according to Ostertag, are never present in the multilocular echinococcus of oxen,[296] in which the separate cysts are larger and the connective tissue integument less powerfully developed.

[296] This may perhaps be explained by the fact that the hosts are slaughtered before the parasites have attained the size or other conditions necessary to disintegration.

Hardly anything positive is known with regard to the development of the alveolar echinococcus; its peculiar conformation is attributed by some to enormous infection of oncospheres, by others to the abnormal situation of one oncosphere; a few authors ascribe it to infection of lymphatic vessels, others to infection of the biliary ducts or to peculiarities of the surrounding hepatic tissue; Leuckart ascribes it to a grape-like variety of form which continues budding; a few more recent authors consider multilocular echinococcus to be specifically different from unilocular echinococcus, and therefore also different the species of Tænia arising from them. Melnikow-Raswedenkow is also of this opinion. According to this author the oncospheres infect the lumen of a branch of the portal vein in Glisson’s capsule of the liver and grow into an irregularly shaped formation (chitinous coil), which breaks through the vascular walls and thus forms the alveoli. So far the data coincide well with Leuckart’s opinion of the original grape-like form of the Echinococcus multilocularis; according to Melnikow-Raswedenkow the “granular protoplasmic substance” (parenchymatous layer) is not only present in the interior of the loculi but also outside, and, moreover, “ovoid embryos” are supposed to develop in the chitinous coils, which, “thanks to their amœboid movements, reach the lumen of a vessel, where, under favourable circumstances, they begin to develop further,” that is to say, they become “chitinous cysts with fantastic outlines,” or also “single-chambered chitinous cysts”; scolices may develop in both. Dévé, however, considers that these embryos are only prolongations of the protoplasmic layer which secondarily cuticularize.

The multilocular echinococcus, which in man produces a severe disease and almost always leads to premature death, infects most frequently the liver, but may also be found primarily in the brain, the spleen and the suprarenal capsule; from the liver by means of metastasis it may reach the most various organs, especially those of the abdomen, but also the lungs, the heart, etc. Up to 1902, 235 cases have been described and up to 1906, 265, being 70 from Russia, 56 from Bavaria, 32 from Switzerland, 30 from the Austrian Alps, 25 from Würtemberg; the remaining cases are distributed over Central Germany, Baden, Alsace, France, Upper Italy, North America. In some the origin is doubtful; in any case after Russia, the mountainous South of Europe is the principal region of distribution. As to the domesticated animals, the same parasite is found principally in the ox (according to Meyer, in Leipzig, in 7 per cent. of the oxen affected with echinococcus); it is rarer in the sheep and very scarce in the pig.

It has already been mentioned above that recently the multilocular echinococcus has been stated to be specifically different from hydatid or unilocular echinococcus. To this may be added the fact that Mangold, who fed a young pig with oncospheres of a Tænia reared from the multilocular echinococcus, found two growths in the liver four months later, which he took to be E. multilocularis, and consequently one has to assume the existence of two different worms. The chief defender of this view, already put forward by Vogler, Mangold, and Müller, is Possett. He bases his opinions on (1) the more restricted distribution of the multilocular hydatid, the former occurring in districts where only cattle are raised, the latter where sheep-breeding is established; (2) that those engaged in looking after sheep are attacked by multilocular, whereas those looking after cattle are attacked by unilocular hydatid; (3) that among the cases of unilocular hydatid occurring in the distribution areas of multilocular hydatid no transitions between the two forms are observed; (4) on the difference in the hooks both in the hydatid as well as in the Tænia stage; the hooks of Tænia echinococcus are plump, sharply curved, and have a short posterior root process the length of which is to that of the total length as 1 to 4·7, whereas on the contrary the hooks of the alveolar echinococcus are more slender, slightly bent, and have a long posterior root process (1 to 2·5); and (5) on the form of the uterus, which in the alveolar Tænia has the form of a spherically distended sac anteriorly.

SERUM DIAGNOSIS OF ECHINOCOCCUS.

(1) Precipitin Reaction.--Mix equal parts of hydatid fluid (of the sheep) and serum of patient. Keep at 37° C. The reaction is not decisive as it may be given by normal sera.

(2) Complement Deviation.--Required: (1) Hydatid fluid of sheep (antigen), (2) guinea-pig complement, (3) patient’s serum, (4) red cells of sheep, (5) hæmolytic serum (of rabbit) against sheep’s red cells, (6) 0·8 per cent. salt solution. Mix the antigen + patient’s serum (heated) + complement + salt solution at 37° C. for one hour. Add red cells of sheep + hæmolytic serum. Allow to stand for half an hour at 37° C. It is imperative to make adequate control observations. An example will indicate the method. Salt solution 1·3 c.c. + patient’s serum (heated) 0·2 c.c. + hydatid fluid 0·4 c.c. + complement 0·1 c.c. of serum diluted to a quarter strength + hæmolytic serum and red cell emulsion 1 c.c. Result: no hæmolysis, i.e., the patient’s serum contains specific (echinococcus) antibodies.

C. *NEMATHELMINTHES*.

BY

J. W. W. STEPHENS, M.D., B.C., D.P.H.

Bilaterally symmetrical animals, without limbs and with a body cavity in which the gut or other organs float. They are generally cylindrical.

Class. *NEMATODA.*

Nemathelminthes with an alimentary canal.

Nematodes are as a rule elongated round worms of a filiform or fusiform shape; their length varies according to the species from about 1 mm. to 40 to 80 cm. The outer surface of the body is smooth or annulated, and at certain points provided with papillæ, occasionally also with bristles and alar appendages. The anterior end carrying the oral aperture is usually rather slender, occasionally quite thin; the posterior end is pointed or rounded; the anus, as a rule, lies somewhat in front of the posterior extremity. The sexes are almost always separate, and the male can as a rule be easily distinguished from the female because the former is smaller and more slender, its posterior extremity is often spiral or incurved, or carries an alar appendage, whereas the female is larger and thicker, and its posterior extremity is straight. In the male the genitalia open into the anus; the sexual orifice of the female opens ventrally along the median line in the anterior half of the body, in the middle, or a little further back. Both sexes, moreover, have an orifice, the excretory pore, which is situated ventrally in the median line and about the level of the œsophageal nerve ring.

In large species, even with the naked eye, two lighter transparent bands--the lateral lines--may be distinguished; they run along the sides of the body from the anterior to the posterior end, while two other bands, the median lines, running along the ventral and dorsal mid-lines, are less evident; in exceptional cases there are also four sub-median lines. These bands or lines are inward projections of the ectoderm, and in them lie the nerves and excretory vessels (fig. 260).

Some Nematodes live free in fresh or salt water, in soil, mud or decaying vegetable matter, others parasitically in the most various organs of animals, frequently also in plants.

ANATOMY OF THE NEMATODES.

All the Nematodes are covered by (1) a CUTICLE, which in the small species is thin and delicate, while in the larger species it is thickened, and may consist of several layers of complicated structure. Canalicular pores do not occur. According to general opinion, which is confirmed by the history of development, the cuticle is a product of (2) the EPITHELIUM or ectoderm that had formerly existed or is still found beneath it; in young specimens and small species it is perceptible, but in older worms it frequently alters so considerably that not only do the borders of the cells disappear,[297] but a fine fibrous differentiation appears in their cytoplasm. The matrix or ectoderm then has the appearance of an ectodermal syncytium permeated by fibres and strewn with nuclei, so that it is hardly distinguishable from the tissue of (3) the CUTIS, which is always present, though developed to a varying degree. Both layers, matrix and cutis, project internally as ridges and form the lateral lines, while the less marked median lines are produced apparently only by the ectoderm (fig. 260).

[297] In the Ascaridæ isolated epidermal cells grow to a considerable size, and have to do with the sensory apparatus of the lips (Goldschmidt).

Unicellular cutaneous glands are known in parasitic as well as in free-living species; they vary in number and arrangement, and are found discharging some at the anterior extremity and others in the vicinity of the genital orifices. In other cases large numbers of them are present along the lateral lines; they are strongly developed in most of the Trichotrachelidæ, where they discharge either along a part of the ventral surface or along the lateral and median lines; they are placed so closely together that the ridges of the cuticle perforated by the orifices have long been known, and have been described, as “rodlet borders,” or “fields of rods.”

As the cutis is immediately adjacent to (4) the DERMO-MUSCULAR TUBE the simple layer of the muscular cells is divided into four quadrants by the longitudinal lines--two dorsal and two ventral (fig. 260). The MUSCLES are in the simplest cases large rhomboid cells that lie two by two in each quadrant, so that on transverse section of the entire worm only eight cells are perceptible. The outer border of the cells is converted into contractile fibrils, while the contiguous inner portion has remained protoplasmic, and contains the nucleus. In large species the muscular cells do not only increase in length (up to 3 mm.) and in number in every quadrant, but their contractile portion curves up to form a groove (like that of a dead leaf) thereby even becoming thicker; simultaneously space is gained for more cells, the protoplasmic parts of these cells (on transverse section) project out of the grooves like vesicles. In all cases there is only one layer of longitudinal muscular cells, which, by contracting, can shorten the body or, by contracting one side, can bend it. In the latter case the muscles of the opposite side have an antagonistic effect, or when all the muscles are contracted, the elasticity of the cuticle acts in the same way. Special muscles exist at the beginning of the gut and at sections of the genital apparatus.

The existence of a cavity between the body and the gut wall has hitherto been generally assumed, and has been referred to the cleavage cavity, and consequently designated as a primary body cavity. More recent investigators, however, state that such a cavity does not exist, but that the space between the longitudinal muscles or their protoplasmic portions and the gut epithelium is filled by a complicated “isolation tissue.” This in the main proceeds from a large cell (Is., fig. 262) which lies directly behind the nerve ring dorsal to the œsophagus, and consists of a system of lamellæ which sheathe the muscles and penetrate through them to the cutis and also cover the gut in a thin layer.

We may now consider the “tuft-like” or “phagocytic” organs, which attain 1 cm. in size, and consist of four, six, or even more ramified cells, which lie close to the walls of the body (fig. 261). They are found either only in the anterior part of the body (Ascaris), or throughout the whole length of the body (Strongylus, syn., Sclerostomum), and their position usually corresponds to the lateral lines. In some species there are small protoplasmic cells on the processes of these organs. In consequence of their size they can be recognized with the naked eye, especially when they are loaded with granules of stain (carmine, Indian ink) injected into the body cavity.

INTESTINAL CANAL.--The oral aperture, which is situated at the tip of the anterior extremity, is frequently surrounded by thick lips, or small bristles, or papillæ; it leads to a more or less strongly developed buccal cavity, which is lined by a continuation of the body cuticle, and which in some species is provided with “teeth,” representing differentiated portions of the cuticle.

THE ŒSOPHAGUS (fig. 262), which arises from the base of the oral cavity, is as a rule a short, bottle-shaped tube with triradiate lumen; its wall is chiefly composed of radiating muscular fibres, which give it the appearance of being transversely striped when viewed from the surface. There exist also in its wall three large gland cells (œsophageal glands) and nerves arising from the lateral lines and running forward. The radial fibres cause a dilatation of the lumen, and exercise an effect antagonistic to the elasticity of the cuticle lining the inner surface. The latter has its own particular layer, which is not in direct connection with that of the oral cavity. Special dilator muscles, arising from the dermo-muscular tube and situated at the commencement of the œsophagus, are only known in a few species. The posterior end of the œsophagus presents a bulb-like dilatation, and is frequently provided with small chitinous movable valves. In a few forms, which belong to the Trichotrachelidæ (Trichocephalus, Trichinella), the œsophagus is a very long cuticular tube, beset on its dorsal surface with a series of large nucleated cells. In others (Cucullanus, Ascaris, etc.), a tube, the so-called glandular stomach, lined only by epithelial cells, follows behind the muscular œsophagus. This glandular stomach is, from its structure, easily distinguished from the mid-gut, or chyle intestine, which is likewise cellular. The so-called mid-gut is a tube lined by flat, cubical, or cylindrical cells (fig. 260) surrounded by “isolation tissue”; its transverse section is circular or flattened dorso-ventrally; the lumen may run in a straight line, or it runs a sinuous course through the alternating prominences of the then flat epithelial cells.

The ectodermal hind gut is, as a rule, very short. At the anal opening the cuticle and the subcuticular layers are reflected inwards, forming the lining of the hind gut. In large species the subcuticular tissue forms large cells on which anteriorly lie in addition large “glandular cells.”[298] In the male the ejaculatory duct opens at this point. Around the end part of the gut, either on the chyle intestine or at the beginning of the end gut, there exists a sphincter muscle arising from a muscle cell which acts antagonistically to the two diaphragm-like dilator muscle cells which stretch from the gut to the body wall. In many species large stretches of the gut are provided with dilator muscles. There is sometimes a retrogressive absorption of the gut in the adult stage of a few parasitic species.

[298] In Ankylostomes according to Looss these cells have no glandular function, but are ligaments.

INTESTINAL CÆCA and ŒSOPHAGEAL GLANDS sometimes exist as intestinal appendages; the former are tubular appendages of various size, running backwards or forwards, and arising from the posterior extremity of the œsophagus. They are lacking in many species. The œsophageal glands are unicellular; a dorsal and two subventral glands may be distinguished according to their position; as a rule they open into the œsophagus at a distance from one another. The body of the gland lies in the bulb of the œsophagus, or in the dorsal cul-de-sac arising from it.

THE NERVOUS SYSTEM is sufficiently known in a few species only; it consists of a ring containing fifty to sixty fibres closely surrounding the œsophagus, various groups of ganglion cells, and a certain number of nerves extending anteriorly as well as posteriorly. The remarkably small number of fibres, as well as ganglion cells, is characteristic of the nervous system of all Nematodes. Immediately behind the œsophageal ring (fig. 263, Lg.) an agglomeration of ganglion cells lies at either side (lateral ganglia); part of their off-shoots form the œsophageal ring, and part are directed posteriorly and ventrally, and unite partly in front of and partly at the back of the excretory pore, with fibres originating direct from the œsophageal ring, and passing along the ventral median line to the back; these fibres then together form the ventral median nerve (fig. 263, V.m.n.). This nerve, originally consisting of thirty to fifty fibres, becomes in the female attenuated quite evenly in its further course. There is also an agglomeration of ganglion cells close in front of the anus (anal ganglia), and then the median nerve divides in order to combine with the lateral nerves on either side. In the male the median nerve enlarges to nearly the original number of fibres in front of the anal ganglion, which contains seven cells; there is also an anal ring embracing the terminal gut, and there are two ganglion cells in it on each side. In the dorsal median line the dorsal median nerve is alike in both sexes; arising in front with a single root from the œsophageal ring, it gathers its fibres from the lateral ganglia; in the anterior part of the body it consists of thirteen to twenty fibres; in the posterior part of the body the fibres are reduced to four or six; behind the anus it divides and combines with the lateral nerves; the latter consists of two fascicles at either side right up to their most posterior extent--one dorsal and one ventral--which in the greater part of the body do not run in, but beside the lateral lines, and exhibit a different origin anteriorly. The ventral fascicle at each side branches off from the ventral median nerve in front of the excretory pore, whereas the dorsal fascicles originate from the œsophageal ring close to the lateral ganglia. Each of the four fascicles contains only two or three fibres, which run backwards parallel to the lateral lines; a few centimetres in front of the caudal extremity they enter the lateral lines and remain separate from one another up to the level of the anal ganglion; here they amalgamate on either side, after each interpolating one ganglion cell, with the single short lateral nerve which first takes up the forked ends of the ventral and then of the dorsal median nerve; finally, both lateral nerves unite with each other at the back in an arch-like manner.

In the male each ventral part of the lateral nerves becomes thickened by taking up fibres from the ventral nerves, which become thickened posteriorly to the nervus bursalis, which towards the middle gives off a mass of fibres to the “genital papillæ” situated in front of and behind the anus; the number of these fibres averages eighty to 100; in its further course the bursal nerve resembles the corresponding ventral part of the lateral nerves of the female.

The ventral and dorsal nerves are connected by a number of semicircular commissures, which originate from the ventral nerves and serve to supply the dorsal nerve, which is always being decreased by fibres departing from it. It is remarkable that these commissures are not placed symmetrically, and their position also is different in the two sexes; in the female there are thirty-one on the right side and only thirteen on the left side. In the male there are thirty-three commissures on the right side and fourteen on the left, which run into the subcuticular layer, generally in pairs, and usually cross at the level of the lateral lines.

The fibres of the two median nerves are chiefly motor; fascicular processes run from each protoplasmic part of the muscular cells to the median nerves; from these they take up bundles of primitive fibrils, which separate, pass through the protoplasmic part and enter the contractile part (fig. 260). One part of the fibrils, however, penetrates beyond the muscles into the subcuticular layer, where they form a network, probably of a sensory nature, with contiguous fibrils. Nerves directed anteriorly finally originate from the œsophageal ring; they consist each of three fibres, carry three ganglion cells at their point of origin, and enter the sensory organs of the three papillæ surrounding the oral aperture. Two of these little trunks lie in the lateral lines, the remaining four are situated in the middle of the four quadrants (Nn. sub-mediani anteriores).

Parasitic species lack higher ORGANS OF SENSE; free-living worms occasionally have two rust-red eyes, sometimes with lenses, at the anterior part of the body. In addition to the above-mentioned sensory papillæ surrounding the oral aperture and the genital papillæ of the male at the end of the body, another pair exist in the vicinity of the lateral ganglia, the “cervical papillæ,” and two dorsal papillæ in the central region of the body and two lateral ones near the tip of the tail (Ascaridæ). The differences in the distribution and number of the sensory papillæ serve for characterizing the larger and smaller groups of Nematodes.

THE EXCRETORY ORGANS of the Nematodes are variable. In a great many cases the apparatus is symmetrical, and consists of a vessel commencing in the posterior extremity in each lateral line (fig. 260), and passing anteriorly. In the vicinity of the anterior extremity both tubes pass out of the lateral lines, bend ventrally, and, in the median ventral line, unite into a short vesicle formed by an ectodermal cell--the cavity of which is lined by a continuation of the cuticle of the body--which opens into the excretory pore (fig. 263, Exp.). Asymmetry is occasioned through the excretory duct proceeding from the ventral pore to the lateral line, and it here proceeds as (or takes up) the left excretory canal, which anteriorly is a broader tube and runs along the left lateral line; shortly before its union with the excretory duct it throws out a branch to the right towards the lateral line, which, however, always remains weak, and runs posteriorly in the right lateral line; a few smaller branches in addition spring from the left main stem. In other species the right branch is completely suppressed; the entire organ thus lies in the left lateral line, and consists of the excretory duct, which occasionally opens quite in front near the lips, as well as the excretory canal, which throws out a number of lateral branches.

This excretory vesicle is a single elongated or horse-shoe-shaped cell, with a large nucleus and an intracellular tubular system, which is connected with the excretory duct arising from the excretory pore on the outer surface (fig. 326). The so-called ventral gland is the only excretory organ of marine Nematodes, and probably represents a primitive form. Goldschmidt, who has investigated the excretory apparatus of Ascaris lumbricoides, considers that the vessels running in the lateral lines are only ducts to which belong a glandular system hitherto overlooked or otherwise interpreted. This system also lies in the lateral lines, and takes the form of two glandular tracts, forming a syncytial tissue in which lie the ducts, one dorsal, one ventral. In parts these tracts are connected by commissures, although their junction with the excretory vessels cannot be clearly made out. These statements, however, require confirmation. The author has further found that the anterior ends of the lateral canals, directly before they bend ventrally, anastomose with one another and give off anteriorly a small blind process, which can be interpreted as a rudiment of a canal coming from the head end, and as a matter of fact, according to Golowin, such anterior excretory canals exist in a number of genera.

In a number of Nematodes (Cheiracanthus, Capillaria, Trichocephalus, Trichinella, etc.), however, special excretory organs are lacking; possibly the cutaneous glands, which are in these species generally powerfully developed, replace these organs.

SEXUAL ORGANS.--With the exception of a few species, the Nematodes are sexually differentiated.

(a) Female Sexual Organs.--The sexual orifice (vulva), surrounded by thick labia, is, as a rule, ventral and varies in position from near the head to near the anus. It leads into a short or long vagina (ectodermic), bifurcating into the two uteri, which may be long or short; the long filiform ovaries are continuations of them (fig. 264). Further there is often, e.g., in Ankylostoma, a differentiation into the following parts: (1) Ovejector: the specialized portion of the uterus before it joins the vagina; there may be a separate one for each uterus, or a common one for both uteri. (2) Seminal receptacle: at the other extremity of the uterus. (3) Oviduct: a narrow tube connecting the ovary with the uterus proper. (For the explanation of the terms convergent and divergent uteri vide footnote p. 432.) Uterus and ovaries, which arise in the first place from a single cell, lie between the body wall and the gut and are surrounded by connective tissue. In some species (for instance, Trichinella) the ovary is single.

At the blind end of the ovary there is a mass of protoplasm with numerous nuclei that multiply continuously. Gradually the nuclei arrange themselves in longitudinal rows (fig. 265) and the protoplasm commences to leave the periphery and surround each nucleus. The nearer to the uterus the more progressive is this loosening process, until club-shaped cells each containing a nucleus are developed. The most pointed end of each, however, is still attached to an axial fibre of protoplasm, the rhachis; probably this has some connection with the nutrition of the ova. Finally the ova fall off and reach the uterus, where they are fertilized and enclosed in shells.

(b) Male Sexual Organs.--There is never more than one testis (fig. 266), which is a straight or sinuous tube of the same construction as an ovary, and in which the mother cells originate in the same manner as the ova. In the same way as the ovary passes into the uterus, so does the testis pass into the spermatic duct; the latter is often divided into the somewhat dilated seminal vesicle and into the muscular ductus ejaculatorius, which, running ventral to the intestine backward (fig. 267), finally opens into the cloaca. In many species, e.g., A. duodenale, the ejaculatory duct is surrounded for a greater or less portion of its extent by the cement gland, the secretion of which (brownish or blackish in colour) serves for copulation. The ejaculatory duct of the large Ascaridæ is for the most of its course surrounded by a muscular network which takes its origin from the two dilator cells of the gut (fig. 268 F.). The spermatozoa of the Nematodes, it may be noted, only attain their full development after the sperm mother cells have been conveyed by copulation into the uteri of the female genitalia. In their form (sheathless, capable of amœboid motion) they differ from those of most other animals.

SPICULES.--The male genital apparatus is also provided with one or two sacs, situated on the dorsal side of the intestine, and opening into the cloaca. In each sac there is a chitinous rod-like body, the spicule. Further, in many cases there exists, more or less fixed in the dorsal wall of the cloaca, a chitinous structure, the accessory piece or gubernaculum, the latter name implying its function of guiding the spicules during copulation (fig. 264A). A special muscular apparatus, consisting of protractors and retractors, moves the spicules. The protractors or exsertors in the large Ascaridæ consist of four flat band-like muscles which surround the spicule sac. Two long muscle cells which arise proportionally far forward on the dorsal side of the lateral line and are inserted into the base of the spicules serve as retractors. The spicules can be projected from the cloacal orifice (anus) during copulation, and when they are introduced into the vagina they serve as prehensile organs, perhaps also as stimulatory organs.

BURSA COPULATRIX.--The males in many genera possess epidermal wing-like appendages at their posterior extremity. These are supported by elongated tactile papillæ called ribs. In the most highly developed bursæ, e.g., in the Strongylidæ, the ribs are called rays, as they consist not only of nerve fibres but mainly of “pulp,” i.e., prolongations of the subcuticular layer. Bursæ are either open, i.e., bilaterally symmetrical, or closed, when the posterior border is continuous all round. A pseudo-bursa is one unsupported by ribs or rays, e.g., in Trichuris. The bursa serves as an organ of prehension during copulation. Some forms, moreover, carry a sucker at the posterior extremity (e.g., Heterakis); in others the spicules and other prehensile organs are absent; they are then replaced by an evertible cloaca, e.g., Trichinella.

DEVELOPMENT OF THE NEMATODES.

After impregnation, the ovum develops around itself a delicate membrane (vitelline membrane), and subsequently an egg-shell is formed. This is derived either as a secretion from the uterine wall or it is a further differentiation of the vitelline membrane, the original single membrane splitting into two, the outer becoming the egg-shell. Further the uterus often secretes a special albuminous covering around the egg-shell. The “yolk” granules of the ovum are secretions of the protoplasm of the ovum itself and first appear when the rhachis is formed. In certain cases ova lie in follicles or capsules formed of epithelium cells derived from the ovarian tubes. These cells subsequently fuse and form a membrane--the CHORION.

The shape of the completed eggs is characteristic of the different species, and therefore a single egg often suffices to diagnose the species. According to the species, the eggs may be deposited sooner or later, either before or during segmentation, or with the embryo perfectly developed. Only a few species are viviparous, e.g., Dracunculus mediensis, Trichinella spiralis; in the other Nematodes the further development of the extruded eggs takes place after various lengths of time in the open, in moist earth, or in water. Thick-shelled eggs can maintain their developmental capacity for a long time, even after prolonged desiccation.

Finally, a nematode-like embryo develops, which usually lies somewhat coiled up within the shell, and varies in its further development according to the species to which it belongs.

In the simplest forms, as in the free-living Nematodes, the embryos, apart from their size, resemble their parents, and grow up into these after leaving the egg-shell. In many parasitical Nematodes, however, the young must be called larvæ, as they present characters which are subsequently lost.

The manner of conveyance of the eggs or the embryos contained in them after they have left the body into the definite host is very different in the various species.

(1) Without Intermediate Host.--(a) In many the conveyance into the definite host is effected directly after the larvæ have developed within the eggs; thus, for instance, the feeding of suitable animals with the embryo-containing eggs of species of Trichocephalus and Ascaris leads to an infection of the gut, for the young Trichocephali or Ascarides only leave the egg-shell when they have attained the intestine of the final host, in which they become adult.

In other cases (b) Ancylostoma, Necator, the larvæ hatch in the open, and live for a time free, changing their form; they grow, cast their skin, and finally gain the intestine of the host by means of water or through the skin, when they lose their larval characters and assume the structure of the adult worm.

(c) In a number of Nematodes, however, HETEROGONY occurs. This terms signifies a mode of development in which two structurally different sexual generations of the same species alternate with each other. To these appertains, for instance, Angiostomum (syn.: Rhabdonema) nigrovenosum, which lives in the lungs of frogs and toads; this Nematode measures about 1 cm. in length and is hermaphrodite (protandric). The eggs are deposited in the pulmonary cavity, and through the cilia of the same reach the oral cavity, where they are swallowed and thus conveyed into the intestine. They pass through the entire gut, and are finally evacuated with the fæces; often, indeed, the young themselves emerge from the egg-shell within the hind-gut of the frogs. These young forms become sexually differentiated, remain much smaller than the parent, their œsophagus is differently constructed (rhabditis form), and they are non-parasitic (fig. 266). After having grown in the open they copulate; the males die soon after copulation, and the females in their own bodies develop a few young, which, given the opportunity to get into frogs, infect them, and are transformed into the hermaphroditic Angiostomum. The same manner of development occurs in other species of the same genus, and also in the case of Strongyloides stercoralis.

(2) With Intermediate Host.--(a) Frequently, however, the larvæ of Nematodes make use of one or even two intermediate hosts; their condition then resembles that of Cestodes or Trematodes, excepting that there is never a multiplication within the intermediate hosts. The larvæ become encapsuled amongst the tissues of the intermediate host, and wait till they are introduced with the latter into the final host. For instance, Ollulanus tricuspis, the adult form of which is found in cats, previously lives encysted in the muscular system of mice. Cucullanus elegans, which attains the adult stage in fishes (perch, etc.), is found encysted in species of Cyclops. Other examples of species that require an intermediate host are Filaria bancrofti and Dracunculus medinensis.

Peculiar conditions prevail in the case of (b) Trichinella spiralis. This species, which in its adult state lives in the intestine of man and of various mammals, is viviparous; the young Trichinæ, however, do not leave the intestine, but reach the intestinal wall (Cerfontaine, Askanazy) in the following way: the female intestinal Trichinæ bore into the intestinal wall, where they are found in the submucosa, or in the lumen of the dilated lacteal vessels. Here the young are born, in the intestinal wall, and leave this position with the lymph stream. Some of them, no doubt, actively bore through the intestinal wall, reaching the lymph or blood-stream, or even pass into the body cavity. What occurs during their further migrations is difficult to say at present. It has hitherto been maintained that the wandering is entirely active; for instance, the ligaturing of an artery would be no protection against the part of the body supplied by such artery being invaded by Trichinella. This observation cannot be otherwise explained than by the active progress of the young Trichinella. The question, however, may be mooted as to where and when the worms quit the blood-vessels, which they for the most part reach through the thoracic duct, the natural connection between the vascular system and the lymphatic system, to wander further independently, and ultimately reach the muscular system, in which they become encysted (fig. 269). Thus the progeny does not leave the body of the host inhabited by the parents, as is generally the case amongst helminthes, but uses it as an intermediate carrier to reach another host, which is then the final host. The latter may belong to another species, or may be another individual of the same species. This second migration is, of course, purely passive.

CLASSIFICATION OF THE NEMATODA.

The Nematodes are usually divided into a number of families, some of which it is at present impossible to define accurately; moreover, the definition of many genera is also in an unsatisfactory state.

Family. *Anguillulidæ*, Gervais and van Beneden, 1859.

A “family” name not definable. They comprise a vast number of small forms, most of which live free in fresh water, in soil, or in macerating substances; amongst them there are some which live parasitically on plants, more rarely on animals. They do not exceed 8 mm. in length. The large majority are only 1 to 2 mm., or even 0·5 mm. The uterus is straight. Eggs in the uterus at one time, one to four. Genera very numerous, but many of them insufficiently defined (Anguillula, Anguillulina, Rhabditis, Heterodera, etc.).

Family. *Angiostomidæ*, Braun, 1895.

Small Nematodes undefined morphologically, but characterized by heterogony, i.e., there is a free-living “rhabditic” generation and a parasitic “filariform” generation which succeed one another (e.g., Angiostomum, Strongyloides, Probstmayria).

Family. *Gnathostomidæ.*

Cuticle covered totally or partly with cuticular laminæ fringed posteriorly with multiple points. Head subglobular, covered with simple spines. Two spicules. Vulva behind middle of body, parasitic in vertebrates, especially mammals (e.g., Gnathostoma, Tanqua, Rictularia).

Family. *Dracunculidæ*, Leiper, 1912.

Males very small in proportion to females. Anus absent. Vulva absent (?). Genera: Dracunculus, Icthyonema (in body cavity of eel and other fish).

Family. *Filariidæ*, Claus, 1885.

Long thread-like Nematodes. Anus present. Œsophagus without bulb. Vulva usually in anterior half of body. Two ovaries. Generally ovoviviparous. Development often requires an intermediate host. This family is at present ill-defined, but has been already subdivided into several sub-families, Filariinæ, Onchocercinæ, Arduenninæ.

Family. *Trichinellidæ*, Stiles and Crane, 1910.

Œsophagus consisting of a chain of single cells, the lumen of the œsophagus passing through their centre. Ovary single. Vulva at junction of anterior and posterior portions. Sub-families: (1) Trichurinæ, (2) Trichinellinæ.

Family. *Dioctophymidæ.*

Body anteriorly armed with spines or unarmed; mouth without lips, with six, twelve, or eighteen papillæ in one or two circles; œsophagus very long without a bulb; anus terminal in female; one ovary; vagina very long; spicule in male very long; bursa cup-shaped without rays (Dioctophyme, Hystrichis, Eustrongylides).

Family. *Strongylidæ*, Cobbold, 1864.

Bursa, supported by rays, always present. Oviparous.

Family. *Physalopteridæ.*

Mouth with two large lips. Bursa with supporting papillæ in form of a lanceolate cuticular expansion, with genus Physaloptera.

Family. *Ascaridæ*, Cobbold, 1864.

Rather thick Nematodes. Mouth with three lips--one dorsal, two latero-ventral. Sub-families: (1) Ascarinæ, (2) Heterakinæ, etc.

Family. *Oxyuridæ.*

Smallish forms, 4 to 45 mm., with cuticle thickened on each side for the whole length of body in the form of a lateral flange or wing. Œsophagus long with a well-marked bulb containing a valvular apparatus. Tail end of female drawn out into a long point. Eggs asymmetrical. Males very small (about 2 mm.). One spicule. Genera: Oxyuris, Passalurus, Ozolaimus, Atractis, etc.

Mermithidæ, greatly elongated “Nematodes,” which, in the larval stage, are parasitic in insects, but in their adult condition are free living. Cuticle with diagonal striation. Without an open mouth or anus. Oral papillæ present. Characteristic eggs with two processes, ending in a tuft of filaments. Larvæ with a movable boring spine at the head end.

Gordiidæ.--Long, thread-like “Nematodes.” Mouth and anterior portion of gut atrophied in adult. Oral papillæ absent.

THE NEMATODES OBSERVED IN MAN.

Family Sub-family Genus Species Anguillulidæ -- Rhabditis R. pellio. R. niellyi. Rhabditis sp. Anguillula A. aceti. Anguillulina A. putrefaciens. Angiostomidæ -- Strongyloides St. stercoralis. Gnathostomidæ -- Gnathostoma Gn. siamense. Gn. spinigerum. Dracunculidæ -- Dracunculus D. medinensis. Filariidæ Filariinæ Filaria F. bancrofti. F. demarquayi. F. taniguchi. F. (?) conjunctivæ. Group. Agamofilaria -- Ag. georgiana. Ag. palpebralis. Ag. oculi humani. Ag. labialis. F. (?) romanorum- orientalis. F. (?) kilimaræ. F. (?) sp. ? (Mikrofilaria) Mf. powelli. Mf. philippinensis. Setaria S. equina. Loa L. loa. Acanthocheilonema Ac. perstans. Dirofilaria Di. magalhãesi. Onchocercinæ Onchocerca O. volvulus. Trichinellidæ Trichurinæ Trichuris T. trichiura. Trichinellinæ Trichinella T. spiralis. Dioctophymidæ -- Dioctophyme D. gigas. Strongylidæ Metastrongylinæ Metastrongylus M. apri. Trichostrongylinæ Trichostrongylus T. instabilis. T. probolurus. T. vitrinus. Hæmonchus H. contortus. Mecistocirrus (Nematodirus) M. fordi. Ancylostominæ Group. Œsophagostomeæ Ternidens T. deminutus. Œsophagostomum Œ. brumpti. Œ. stephanostomum var. thomasi. Œ. apiostomum. Group. Ancylostomeæ Ancylostoma A. duodenale. A. ceylanicum. A. braziliense. Group. Bunostomeæ Necator N. americanus. N. exilidens. Group. Syngameæ Syngamus S. kingi. Physalopteridæ -- Physaloptera P. caucasica. P. mordens. Ascaridæ Ascarinæ Ascaris A. lumbricoides. A. sp. A. texana. A. maritima. Toxascaris T. limbata. Belascaris B. cati. B. marginata. Lagocheilascaris L. minor. Oxyuridæ -- Oxyuris O. vermicularis. Mermithidæ -- Mermis M. hominis oris. (Agamomermis) Ag. restiformis.

Family. *Anguillulidæ.*

Genus. *Rhabditis*, Dujardin, 1845.

Buccal cavity elongated, with lips. Its chitinous wall uniformly thick. Lateral lines absent. Males with bursa.

*Rhabditis pellio*, Schneider, 1866.

Syn.: Pelodera pellio, Schn., 1866; Rhabditis genitalis, Scheiber, 1880; Rhabditis pellio, Schn., 1866.

Males 0·8 to 1·05 mm. in length; females, 0·9 to 1·3 mm. in length. The posterior extremity of the body of the male has a heart-shaped bursa, and seven to ten ribs on each side; the bursa may, however, be lacking. The spicules measure 0·027 to 0·033 mm. in length, but are never quite alike. The posterior extremity of the female is long and pointed; the vulva lies somewhat behind the middle of the body, the ovary is single, the eggs are oval, 60 µ by 35 µ.

This species was found in Stuhlweissenburg by Scheiber in the acid urine (containing albumin, pus and blood) of a woman suffering from pyelonephritis, pneumonia and acute intestinal catarrh; the observer was able to convince himself that the Nematodes which were found during the whole period of the illness lived in the vagina, and were evacuated with the urine.

Oerley proved that this species had long been known; during its larval stage (Anguillula mucronata, Grube, 1849) it lives in earthworms; in its adult stage it lives in decomposing matter in the soil. By introducing individuals of this species into the vagina of mice, Oerley succeeded in obtaining infection and multiplication (facultative parasitism). These Nematodes must in some such way have got into the vagina of Scheiber’s patient.

Two other cases described by Baginsky and Peiper probably belonged to the same or a nearly related species.

*Rhabditis niellyi*, Blanchard, 1885.

Syn.: Leptodera niellyi, Blanchard, 1885.

In 1882 Nielly had a cabin-boy, aged 14, under observation in Brest. The lad had never left the neighbourhood of Brest, and had suffered from itching papules on the skin for five or six weeks; in the papules the observer found one or several rhabdites, measuring 0·33 mm. in length by 0·30 mm. in breadth. Their cuticle presented a delicate transverse striation; the intestine was the only internal organ recognizable, and it opened somewhat in front of the posterior extremity. Therefore, it must have belonged to the rhabditis-like larva of a Nematode, the adult stage of which is unknown.

The manner of infection was established almost certainly by a further observation of Nielly’s: at the commencement of the illness small Nematodes were found in the blood of the patient; later on, however, they disappeared, neither were Nematodes found in the fæces, urine or sputum. Therefore it must be concluded that the cabin-boy, who was in the habit of drinking water from brooks, had thus ingested embryo-containing eggs of a Nematode; the young hatched out in the intestine, perforated it, reached the blood and then settled in the skin; but, on the other hand, the entry may have been direct through the skin.

In connection with the foregoing, reference should be made to a communication by Whittles, insufficient from a zoological point of view. In a case of hypertrophic gingivitis occurring in a female patient, aged 19, who had never left Birmingham, he found Nematode larvæ in the periosteum of the upper jaw, which was excised after extraction of the right premolar; the genital rudiment could be recognized in them. Similar larvæ were found in the same patient in abscesses in various regions of the skin, and in the case of her mother in the blood. The author considers that the infection took place through a dog, and refers to the case of O’Neil (1875), who found Filariæ in the skin (in the condition known as “craw-craw”), referred by Manson to Filaria perstans. O’Neil’s case was quoted, and attributed to Filaria sanguinis hominis. In conclusion, the author states that he has repeatedly found Nematode larvæ in the blood of persons who suffered from pruritus; in his opinion the parasite had been imported through the agency of troops returned from South Africa. Glatzel found true Filaria larvæ in a pustule of a cutaneous eruption of the trunk and extremities in a patient at Dar-es-Salam.

Skin diseases which are caused by young Nematodes are also observed in dogs (Siedamgrotzky, Möller, J. G. Schneider, Künnemann), foxes (Leuckart), and horses (Semmer). Zürn found young Nematodes (Anguillulidæ) also in pig’s flesh. In Künnemann’s case it was shown that the adult Rhabdites lived in the straw upon which the dog lay.

*Rhabditis*, sp.

In the fluid obtained by lavage from the stomach of a female patient, aged 16, suffering from ozæna, O. Frese found during two consecutive months Rhabdites of various ages, 0·275 to 0·64 mm. in length, the adults all with eggs; males were not found; transmission into rabbit’s stomach failed, but they could be kept alive in much diluted hydrochloric acid (2 : 1,000) for several weeks. Neither eggs nor larvæ appeared in the fæces of the patient. The nature of the infection, which was perhaps of unique occurrence, remained doubtful.

Genus. *Anguillula*, Ehrenberg, 1826.

Buccal cavity very small, without lips. Males without bursa, but with a series of papillæ. Lateral lines absent.

*Anguillula aceti*, Müller, 1783.

Cuticle unstriped, body cylindrical, anterior end tapering but little, posterior end long, pointed. Male up to 1·45 mm. long, 0·024 to 0·028 mm. wide; two pre-anal papillæ, one post-anal; spicules equal, curved, 0·038 mm. long; gubernaculum present; testis extending in front of mid-line of body. Female up to 2·4 mm. long, 0·040 to 0·072 mm. wide; anterior uterus reaching to near the œsophagus, posterior to hind gut. Viviparous; embryos in both or only in one uterine horn, 0·22 mm. long, 0·012 mm. broad.

The species is a frequent inhabitant of vinegar (prepared by older methods), and was once observed for some time by Stiles and Frankland in the urine of a woman; the urine had an acid reaction, and once had a distinct odour of vinegar. It was assumed that the patient, who was hysterical and suffered from chronic nephritis, employed vaginal douches with diluted vinegar, perhaps to deceive her physician or to protect herself against conception. According to Ward, Billings and Miller are said to have reported on two other cases. Ill-effects which might be connected with the vinegar eel (Anguillula aceti) were not present.

Genus. *Anguillulina*, Gervais and Beneden, 1859.

Syn.: Tylenchus, Bastian, 1864.

Characterized by the possession in the buccal cavity of a spine knobbed posteriorly; bursa present; uterus asymmetrical. Numerous species parasitic in plants.

*Anguillulina putrefaciens*, Kühn, 1879.

Syn.: Tylenchus putrefaciens, Kühn; Trichina contorta, Botkin, 1883.

In 1883 Botkin (Pet. klin. Wochenschr., 1883) found a small Nematode, which was, however, entirely mistaken, in the material vomited by a Russian; this was not a species of Trichinella, but an Anguillulina living in onions which had already, in 1879, been described by Kühn as Tylenchus putrefaciens; the Nematodes got into the stomach with the onions, causing nausea and vomiting.

Family. *Angiostomidæ*, Braun, 1895.

Genus. *Strongyloides*, Grassi, 1879.

Syn.: Pseudorhabditis, Perroncito, 1881; Rhabdonema, Leuckart, 1882, p.p.

The genus is insufficiently defined. The parasitic form possesses a simple mouth opening directly into the long cylindrical œsophagus which occupies the anterior third of the body. The free-living forms possess a small buccal cavity; the œsophagus is short, with a double bulb, in the hinder one there is a *Y*-shaped chitinous valve; two spicules of equal size.

*Strongyloides stercoralis*, Bavay, 1877.

Syn.: Anguillula intestinalis et stercoralis, Bavay, 1877; Leptodera intestinalis et stercoralis, Cobb.; Pseudorhabditis stercoralis, Perroncito, 1881; Rhabdonema strongyloides, Leuckart, 1883; Strongyloides intestinalis, Grassi, 1883; Rhabdonema intestinale, Blanchard, 1886.

In 1876, a number of French soldiers returned to Toulon from Cochin China suffering from severe diarrhœa. Dr. Normand, under whose treatment they were, discovered a large number of Nematodes in the evacuated fæces, and Bavay described them as Anguillula stercoralis. Soon after Normand, at the post-mortem of five patients who had died of Cochin China diarrhœa, found numerous other Nematodes in the intestine, from the stomach to the rectum, in the bile-ducts and in the pancreas, and these he handed over to Bavay. The latter diagnosed another species, and described them as A. intestinalis. Both forms were then regarded as the cause of Cochin China diarrhœa until, in 1882, Leuckart was able to demonstrate that the two forms are only two succeeding generations of the same species, of which the one (A. intestinalis) lives parasitically in the intestine, whereas its young (A. stercoralis) attain the open, where they come to maturity and propagate. The young of these again live parasitically. There thus exists the same heterogony as was discovered by Leuckart in Angiostomum nigrovenosum of frogs, which heterogony, indeed, according to v. Linstow, appertains to the entire family of the Angiostomidæ.

(1) The parasitic generation (strongyloid or filariform ♀) is quite colourless and cannot be seen in situ even with a lens. To detect them it is necessary to scrape the mucosa of the jejunum and examine the scrapings microscopically. It measures 2·2 mm. in length, and 34 µ to 70 µ in breadth; the cuticle is finely transversely striated; the mouth is surrounded by four lips; the œsophagus is almost cylindrical and a third the length of the entire body. The anus opens shortly in front of the pointed posterior extremity; the vulva is situated at junction of middle and posterior thirds of the body; the uterus has no special ovejector; the eggs measure 50 µ to 58 µ in length, and 30 µ to 34 µ in breadth, and lie in a chain one behind the other (fig. 270). As in the case of Angiostomum nigrovenosum, Leuckart considers this stage to be hermaphroditic, the testes degenerating after having functioned; other authors (Rovelli) regard it as a female reproducing by parthenogenesis.

(2) The free-living generation (♂ and ♀) has a smooth body, cylindrical, somewhat more slender at the anterior extremity and pointed at the tail end. The mouth has four indistinct lips; the œsophagus is short with a double (rhabditis-like) bulb; there is a *Y*-shaped valve in the posterior bulb; the anus opens in front of the tail end. The males measure 0·7 mm. in length, 0·035 mm. in breadth. Their posterior end is rolled up; the two brown spicules are small (38 µ) and much curved. There is also a gubernaculum. The females measure 1 mm. in length or a little over; 0·05 mm. in breadth. The tail end is straight and pointed; the vulva lies somewhat behind the middle of the body. The yellowish, thin-shelled ova measure 70 µ in length and 45 µ in breadth.

As Askanazy has shown, the parasitic form bores deeply into the mucous membrane of the intestine, and frequently into the epithelium of Lieberkühn’s glands, both for nourishment and oviposition. The eggs then develop in the intestinal wall. The eggs which are found in scrapings from the mucosa occur, at least in the case of Strongyloides of the sheep, in chains enclosed in a thin tube or sheath, the origin of which is doubtful; possibly it is the uterus. The eggs themselves are only rarely found in stools, e.g., after a strong purge. The larvæ, which are hatched out, and measure 0·2 to 0·25 mm. long by 0·016 mm. broad, again reach the lumen of the intestine,[299] and grow to double or three times that size, until they are passed out with the fæces. They already differ from the parent (♀) in the shape (rhabditiform) of the œsophagus. When the external temperature is sufficiently high (26° to 35° C.), they become sexually mature after moulting. In about thirty hours they are completely developed and copulate, now forming the free-living rhabditiform generation. At lower temperatures the larvæ only moult, but do not escape from the old cuticle and do not develop further. At a temperature of about 25° C. only some of the larvæ attain maturity.

[299] As a case published by Teissier shows, they may also abnormally appear in the blood (Arch. méd. expér. et d’An. path., 1895, vii, p. 675).

The females of the free-living generation (rhabditiform) deposit from thirty to forty eggs, which develop rapidly, sometimes even within the uterus in the case of old females. After the larvæ have emerged from the egg-shell, they measure 0·22 mm. in length, and possess the characteristics of the parents (rhabditiform larvæ). When they have grown to 0·55 mm. they moult, and while losing their own characteristics they acquire the characteristics of their parasitic grandparents (strongyloid or filariform). After about eight days the free-living adult generation in the cultures have disappeared, and all the rhabditiform larvæ have been transformed into strongyloid or filariform larvæ; they then die off unless they reach the intestine.

This cycle of development holds good for Strongyloides stercoralis of tropical origin (Bavay, Leuckart, Leichtenstern, Zinn). In the European Strongyloides the free-living generation, as a rule, is absent (Grassi, Sonsino, Leichtenstern, Braun); the rhabditis-like larvæ evacuated with the fæces are transformed into the strongyloid or filariform type of larva (in cultures which are easily made) which will only become adult if introduced into man.

So that we have these two cycles: (A) (1) ♀ parasitic, (2) eggs, the rhabditiform larvæ in fæces, (3) free-living strongyloid or filariform larva, (4) ♀ parasitic. (B) (1) (2) (3) as before, then (4) adult ♀ and ♂, free living, (5) eggs, (6) rhabditiform larva, (7) strongyloid or filariform larva, (8) ♀ parasitic.

Infection of man results not only from direct entry into the stomach but also, according to van Durme and Looss, through the skin.

Occurrence in Man.--As already mentioned, Strongyloides stercoralis was first observed in persons suffering from so-called Cochin China diarrhœa. From the enormous numbers of parasites evacuated with the fæces, the cause of the disease was apparently evident. It appeared, however, that only some of the soldiers returning from Cochin China and Martinique, and suffering from diarrhœa, harboured Strongyloides (Chauvin). Breton made the same observations in Cochin China and found that only 10·4 per cent. of cases of chronic dysentery, and 8·8 per cent. of chronic diarrhœa, show Strongyloides. Normand, moreover, found that only a few of the Europeans residing in Cochin China are exempt from S. intestinalis, yet the people exhibit no intestinal symptoms; if, however, from any cause a catarrhal condition of the intestine supervenes the condition is changed, the parasites appear in larger numbers, and the disorder is considerably intensified.

S. intestinalis, besides being present in the Indo-China region, also occurs in the Antilles, in Brazil, Africa, and Europe; in 1878 it was discovered in Italy by Grassi and C. and E. Parona; in 1880 it was also found in the labourers working at the St. Gothard tunnel. It was imported into Germany, Belgium, and the Netherlands by Italian labourers. One sporadic case has been observed in East Prussia, and the worm has also been reported from Siberia.

In mammals the following species are found: Probstmayria (Strongyloides) vivipara, Ransom, 1907, in Equus caballus; Strongyloides fülleborni, v. Linst., in Anthropopithecus troglodytes and Cynocephalus babuin.

Their development is, so far as is known, the same as that of Strongyloides stercoralis (v. Linstow, Centralbl. f. Bakt., Path. u. Infektionsk., 1905, Orig. xxxviii, p. 532).

Family. *Gnathostomidæ.*

Genus. *Gnathostoma*, Owen, 1836.

Syn.: Cheiracanthus, Diesing, 1839.

Easily recognizable by the numerous spines which cover the entire body or only the anterior extremity, and terminate in several points; head globular and beset with bristles; mouth with two lips; two spicules; vulva situated behind the middle of the body.

*Gnathostoma siamense*, Levinsen, 1889.

Syn.: Cheiracanthus siamense, Lev., 1889.

Female measures 9 mm. in length, 1 mm. in breadth. There are eight rows of simple spines on the head; the armature of spines extends over the anterior third of the body only; each spine on the anterior region of the body spreads into three points, of which the middle one is the longest; the posterior spines are simple; they gradually become smaller and then disappear entirely. The vulva is situated behind the middle of the body.

Male.--10·5 mm. long by 0·6 mm. broad. Head terminates in a globular swelling with two large lips. Neck 3 mm. broad. In front of neck eight rows of simple spines directed backwards. Anterior half of body with cuticular laminæ, posterior unarmed. Two pre-anal and two post-anal papillæ. Bursa wanting.

Spicules 1·1 and 0·4 mm. respectively.

Leiper considers Gnathostoma siamense to be identical with Gnathostoma spinigerum.

The single specimen described by Levinsen was found by Deuntzer in Bangkok (Siam), and was obtained from a young Siamese woman who suffered from a small tumour of the breast which had developed in the course of a few days. After the disappearance of the tumour, nodules the size of beans were found in the skin; out of one of these the worm was obtained. The same observer saw this affection in two other persons.

A closely related species, Gnathostoma spinigerum, Ow., lives in the stomach of wild cat (Felis catus), puma (Felis concolor), tiger (Felis tigris), and domestic cat (India); another species, Gnathostoma hispidum, Fedsch., 1839, in the stomach of pigs in Turkestan, Annam, Hungary, Congo, and by Collin in the stomach of an ox (Berlin).

Gnathostoma sp. in pariah dogs, Calcutta. Gnathostoma sp. in monkeys, French Guiana. They produce large fibrous thickenings in the stomach wall.

*Gnathostoma spinigerum*, Owen, 1836.

Cuticle of bulb with eight rows of chitinous laminæ with their posterior edges notched into spines. The laminæ on the anterior portion of the body are similar trident laminæ. In the middle of the body, the laminæ are simple and conical, cuticle posteriorly is unarmed. Mouth with two fleshy lips.

Male 5 mm. long by 0·5 mm. broad; tail spiral, four pairs of papillæ.

Female about twice as long; tail straight, trilobed.

Family. *Dracunculidæ*, Leiper, 1912.

Genus. *Dracunculus*, Kniphoff, 1759.

Anterior end rounded with a cuticular thickening or shield. Mouth triangular with two lips. Alimentary canal atrophied.

*Dracunculus medinensis*, Velsch, 1674.

Syn.: Vena medinensis, Velsch, 1674; Dracunculus persarum, Kämpfer, 1694; Gordius medinensis, Linné, 1758; Filaria dracunculus, Bremser, 1819; Filaria æthiopica, Valenciennes, 1856; Dracunculus medinensis, Cobbold, 1864; Guinea worm, Medina worm.

The females attain a length of 50 to 80 cm., or even more, and average 1·5 to 1·7 mm. in diameter. They are whitish or yellowish in colour. The anterior extremity is roundish and bears a cuticular thickening or shield. The triangular mouth opening is surrounded by two projections or lips, behind which on the shield there are two lateral and four sub-median papillæ; the posterior end terminates in a spine, ventrally directed, and about 1 mm. in length; the alimentary canal below the œsophagus is atrophied, but not entirely obliterated; anus absent; the lateral lines are very flat. The greater part of the body is occupied by the long uterus, in which a great number of young larvæ are always found. The ovaries probably lie at the ends of the uterus; the vulva lies just behind the cephalic shield. During parturition the uterus is prolapsed through this opening.

The male is almost unknown. Leiper in an experimentally infected monkey found two males 22 mm. long, one from the psoas muscle, the other from the connective tissue behind the œsophagus.

Occurrence.--Filaria medinensis has been known since the most remote period. The “fiery serpents” that molested the Israelites by the Red Sea, and which Moses mentioned, were probably filariæ. The term Δρακὁντιον occurs in Agatharchides (140 B.C.). Galen called the disorder dracontiasis; the Arabian authors were well acquainted with the worm. It is found not only in Medina or Arabia, but also in Persia, Turkestan, Hindustan. The Guinea worm is also widely distributed in Africa, on the coasts as well as in the interior. It occurs in the Fiji Islands. It was carried to South America by negro slaves, but is said at the present time to exist in only quite a few places (British Guiana, Brazil [Bahia]); it is also observed in mammals (ox, horse, dog, leopard, jackal [Canis lapuster], etc.).

Dracunculus medinensis in its adult stage lives in superficial ulcers on the body surface; it is seen most frequently on the lower extremities, more especially in the region of the ankle, but it also occurs in other parts of the body--on the trunk, scrotum, perineum, on the upper extremities, and in the eyelids and tongue. Sometimes there is only one ulcer and one worm, but more commonly several. It attacks man without distinction of race, age or sex. It is observed most frequently during the months of June to August.

Life history.[300]--When about a year old the worm seeks the surface of the body and produces there a thickening as big as a florin. Over this a vesicle forms which eventually ruptures, and at the bottom of the ulcer can be seen a hole from which a part of the worm may project. On bathing the sides of the ulcer with water, a drop of fluid, at first clear then milky, exudes. This contains numerous larvæ. In other cases a thin tube an inch long is prolapsed (through the vulva). This is probably the uterus, but the mechanism of parturition is not clearly known. It lasts for about a fortnight. An abundant supply of larvæ can be got by placing wet compresses on a fresh ulcer. In a few hours a mass of larvæ is obtained.

[300] The larvæ resemble those of Cucullanus elegans parasitic in the perch (Perca fluviatilis). The larvæ of this species develop in Cyclops sp. Fedschenko in 1870, at Leuckart’s suggestion, succeeded in observing the invasion of Cyclops by Guinea worm larvae. They penetrate not per os but through the exoskeleton. Newly hatched larvæ (in bananas) will cause infection of monkeys.

The larvæ are 500 µ to 750 µ by 15 µ to 25 µ, with a long slender tail about one-third of the total length. The cuticle is transversely striated. The body is flattened. They possess an œsophagus and gut. At the anus there are apparently glandular structures.

The larvæ live and move actively in water for about two days, the majority dying on the third (Leiper). If a number of Cyclops sp. have been collected and isolated in clean water, and the larvæ are now added, the further development can be traced.

The larvæ enter the Cyclops, according to most authorities, by penetrating the exoskeleton, but according to Leiper this is impossible; they must enter by the mouth and penetrate the gut in order to reach the body cavity. In eight days moult 1 takes place, the striated cuticle being cast off. In ten days moult 2 takes place. In five weeks the larva is mature. If now the infected Cyclops is placed in 0·2 per cent. HCl solution the Cyclops is killed immediately, but the larvæ are stirred into activity, escape from the body, and swim about in the acid. This suggests that infection in nature probably takes place by the swallowing of infected Cyclops; Leiper, by feeding Cyclops containing mature larvæ to a monkey, found in it, post mortem six months later, two immature females 30 cm. long and two males 22 mm. long.

In certain areas the new cases occur principally in June. Five weeks later the larvæ will become mature in Cyclops, so that infection of Cyclops is taking place in July or August, and from then to June about ten months elapse, giving the period of development in man.

Pathology.--The initial induration is accompanied by itching. Urticarial eruptions are described in Dahomey and Mauretania accompanied by fever, rigors, blood-shot conjunctiva, and prostration resembling fungus poisoning. Symptoms last for one to two days, later the worms appear on the surface.

If the worm is ruptured in an attempt to extract it, disastrous results may occur through the escape of the larvæ into the tissues: fever, inflammation, abscess, sloughing, ankylosis, even death from sepsis. Eosinophilia is often marked, 11 to 13 or even 50 per cent.

Extraction.--(1) The native method consists in rolling the worm round a stick; 1 in. to 2 in. are extracted each day, the process taking about a fortnight; (2) Emily used injections of 1 in 1,000 sublimate into the swelling or into the worm itself fixed by a ligature. (3) Béclère chloroforms the worm; (4) the worm can be more easily removed when all the embryos have been deposited (two to three weeks).

Cyclopidæ.--Cephalothorax ovate, clearly separated from abdomen. Anterior antennæ of female when bent back scarcely ever stretch beyond the cephalothorax. The second antennæ are unbranched. First four pairs of feet two-branched, outer branches three-jointed. The fifth pair of limbs are rudimentary alike in both sexes, usually one-jointed. There is no heart. The female has two egg sacs containing about fifty eggs.

Genus. *Cyclops*, Müller, 1776.

Mandible palp rudimentary, reduced to a tubercle bearing two branchial filaments. Maxillary palp rudimentary (obsolete). Lower foot-jaw non-prehensile. Head ankylosed to first thoracic segment.

Family. *Filariidæ.*

Sub-family. *Filariinæ.*

The residue after exclusion of the Arduenninæ and Onchocercinæ.

Genus. *Filaria*, O. Fr. Müller, 1787.

Very long, slender Nematodes, without excretory vessels or excretory pore, the males of which are usually considerably smaller than the females. Mouth round, without lips, unarmed. The lateral lines occupy one-sixth of the circumference of body. The tails of the males are bent or spirally rolled, and bear little wing-like appendages. The two spicules are unequal; almost always there are four pre-anal papillæ, but the number of post-anal papillæ varies. The vulva is always situated at the anterior extremity. Parasitic chiefly in the serous cavities and in the subcutaneous connective tissue. Insufficiently defined.

*Filaria bancrofti*, Cobbold, 1877.

Syn.: Trichina cystica, Salisbury,[301] 1868 (nec Filaria cystica, Rud., 1819); Filaria sanguinis hominis, Lewis, 1872; Filaria sanguinis hominis ægyptiaca, Sonsino, 1875; Filaria wüchereri, da Silva Lima; Filaria sanguinis hominum, Hall, 1885; Filaria sanguinis hominis nocturna, Manson, 1891; Filaria nocturna, Manson, 1891.

[301] C. W. Stiles (“American Medicine,” 1905, ix, p. 682) is of the opinion that Salisbury’s Trichina cystica is identical with Oxyuris vermicularis.

These parasites of man were for a long time only known in their larval stage. They were discovered in 1863 in Paris by Demarquay, in the hydrocele fluid of a Havanese emptied by puncture; they were next observed by Wücherer, in Bahia, in the urine of twenty-eight cases of tropical chyluria; they were likewise observed in North America by Salisbury, who gave them the name of Trichina cystica. The next discoveries (in Calcutta, Guadeloupe, and Port Natal) related to chyluria patients, until Lewis discovered the larvæ in the blood of man (India), and found they were almost always present in persons suffering from chyluria, elephantiasis, and lymphatic enlargements; he also, in exceptional cases, found them in apparently healthy persons (Filaria sanguinis hominis). Lewis and Manson studied the disease and the filariæ of the blood very minutely, and became aware that the filariæ were sucked up by mosquitoes with the blood. Manson described the metamorphoses that take place within the body of the mosquito. The adult female was discovered in Queensland by Bancroft, and soon after Lewis found it in Calcutta; it was described by Cobbold as F. bancrofti. The male was first seen by Bourne in 1888.

Head bougie-like, i.e., separated by a narrowing from the neck, having two rows of minute papillæ. Cuticle has extremely fine striations.

Female.--50 to 65 mm. long by 1·5 to 2 mm. broad. Vulva 0·4 to 0·7 mm. behind the head. Anus about 1/4 mm. from the tip of the tail (vulva 1 to 1·3 mm. from head, and anus 0·17 to 28 mm. from tail according to other authors). The vagina is a muscular tube forming three bold loops, and has terminally a pyriform enlargement. Uterus double (or single). Ovoviviparous.

Male.--25 to 30 mm. long by 0·1 mm. thick (40 by 0·1 mm. according to various authors). Probably two pairs of pre-anal papillæ, eight pairs of peri-anal, two pairs of post-anal papillæ, and one pair terminal. Tail curved. Two spicules, 0·2 and 0·6 mm. respectively, and a cup-like gubernaculum. The long spicule is cylindrical, expanded proximally and tapering distally to a filament with wings. At the tip it is spoon-like. The short spicule is of the same diameter throughout. It is gutter-like, coarsely marked. Testis uncoiled, terminating in a snowdrop-like process (Leiper).

Eggs.--40 µ by 25 µ. They do not appear to possess a true shell, but only an embryonal or vitelline membrane secreted by the ovum.

Embryos.--In the posterior part of the uterus eggs occur, in the anterior part embryos; the larvæ at birth measure 127 µ to 200 µ by 8µ to 10 µ. In the blood they measure in the fresh 260 µ by 7·5 µ to 8 µ. In stained films, owing to shrinkage, there is great variation in size, from 154 µ to 311 µ. Probably 260 µ to 285 µ is the average in stained films.

Geographical Distribution.--Europe: Two cases recorded, one from near Barcelona. The patient suffered from hæmato-chyluria and enlarged scrotum with mikrofilariæ in the blood. A second case from Siena. Africa: The filarial index has not been estimated for various parts. In Nigeria it is about 10 per cent.

Habitat.--Lymphatic glands: e.g., inguinal, femoral, iliac, lumbar, mesenteric, bronchial, superficial cervical, epitrochlear.

Lymphatic vessels: e.g., those draining into the receptaculum chyli of the spermatic cord, in the thoracic duct and in various different parts.

Organs, etc.: Testis, epididymis, spermatic cord, tunica vaginalis, mammary cyst, and in abscesses.

They may occur in masses, but usually only a few (one to eight). Females are commoner than males. Dead and calcified worms are common in the various sites.

Distribution of Larvæ in Body.--These are by no means uniformly distributed, but occur in greater number in the capillaries of the lungs. Besides the lungs they occur in the capillaries of other organs, as the following data of Rodenwaldt show:--

Mikrofilariæ Mikrofilariæ Lungs 134,821† Spleen 1,666 Liver 4,884 Brain 3,833 Kidneys 15,253 Glands 0 {Glomeruli 8,008 Marrow 0 {Parenchyma 7,245 Blood 3,000

† These figures refer to 1 c.c. of each organ, and were estimated by cutting sections of definite thickness (30 µ to 40 µ) and counting the filariæ in a definite area of section, e.g., 1/4 cm.^2 The organs before removal from the body have their vessels tied, and are then fixed in hot alcohol.

The following data of Rodenwaldt refer to the larvæ of Filaria immitis in the dog. They are commoner in organs than in vessels, and especially in the capillaries of the organs, but in the lungs they appear to be equally distributed in capillaries, arteries and veins.

The length of life of larvæ is unknown, but they appear to be destroyed in the kidneys, as dead calcified specimens are fairly numerous in the capillaries of the vasa recta of the medullary substance.

Kidneys: mainly in the glomerular capillaries and those of the vasa recta.

Liver: in the capillaries of the portal system, especially in those between the interlobular and the central intralobular veins.

Periodicity of Larvæ.[302]--Roughly speaking, the larvæ of Filaria bancrofti are found in the peripheral blood only during the night, disappearing (but not entirely) during the daytime. Their periodicity and that of Loa loa larvæ is shown by the table on p. 394, based on that of Smith and Rivas (Amer. Journ. Trop. Dis. and Prev. Med., 1914, vol. iii, p. 361).

[302] For determining periodicity measured quantities of blood, e.g.., 20 mm.^3, should be used. A thick film is made of the whole quantity. The numbers present in this quantity may vary from three or four to 300 or 400.

It was discovered by Mackenzie that this periodicity could be reversed by making the patient sleep during the daytime, showing that the phenomenon was in some way dependent on sleep or its attendant phenomena. Rodenwaldt gives the following explanation of the phenomenon of periodicity:--

Mikrofilariæ come to rest in capillaries. After passing up the thoracic duct they would reach the capillaries of the lungs by the superior vena cava. Here they occur in immense numbers. In the case of Loa loa larvæ (which have a diurnal periodicity) some of these are forced out by the increased force and rapidity of the pulmonary circulation during the day, but are able to rest (owing to their sticky sheath?) in the peripheral capillaries on their way to the capillaries of the organs. During the night the force of the current through the lungs is relaxed and consequently they are able to remain in the pulmonary capillaries and do not appear in the capillaries of the systemic circulation. If it is true that the periodicity of Loa loa cannot be reversed by changing the hours of sleep, then the explanation is incomplete. In the case of the larvæ of Filaria bancrofti (which have a nocturnal periodicity), in order to apply the same explanation we must further assume that the mikrofilariæ have less power of resisting the force of the capillary current (i.e., are less sticky). They are washed out of the pulmonary capillaries by day and by night, but it is only at night, when the blood stream in systemic capillaries is less rapid, that they are able to rest there. In the daytime they are washed on until they reach the capillaries of the organs (possibly again the lungs). The reversal of the periodicity by sleeping during the daytime admits of a similar explanation. If this explanation be true, then a prolongation of the day conditions, e.g., by continued exercise, should result in still keeping the larvæ out of the circulation, but this does not appear to be the case.

--------+----------+----------+----------+----------+----------+---------- | Larvæ of | Average | CASE 1. | Average | CASE 2. | Average | L.loa | 132. | _F. | 1,000 | F. | 1,570 | in equal |Deviations|bancrofti| (about). |bancrofti_| (about). |quantities| from | larvæ |Deviations| larvæ |Deviations | of blood | average |in 1 c.c. | from |in 1 c.c. | from | | | of blood | average | of blood | average --------+----------+----------+----------+----------+----------+---------- 2 a.m. | 9 | - 123 | 3,500 | + 2,500 | 6,500 | + 3,930 4 a.m. | 11 | - 121 | 3,200 | + 2,200 | 5,200 | + 3,630 6 a.m. | 41 | - 91 | 2,800 | + 1,800 | 2,000 | + 430 8 a.m. | 168 | + 36 | 900 | - 100 | 1,100 | - 470 10 a.m. | 298 | + 166 | 210 | - 790 | 350 | - 1,220 12 noon | 531 | + 389 | 30 | - 970 | 50 | - 1,520 2 p.m. | 252 | + 120 | 20 | - 980 | 40 | - 1,530 4 p.m. | 146 | + 14 | 10 | - 990 | 30 | - 1,540 6 p.m. | 91 | - 41 | 40 | - 960 | 40 | - 1,530 8 p.m. | 23 | - 99 | 60 | - 940 | 100 | - 1,470 10 p.m. | 5 | - 127 | 600 | - 400 | 800 | - 770 12 mid- | 5 | - 127 | 750 | - 250 | 2,600 | + 1,030 night| | | | | | --------+----------+----------+----------+----------+----------+---------- Total | 1,580 | -- | 12,120 | -- | 18,810 | -- --------+----------+----------+----------+----------+----------+----------

In certain countries, e.g., Fiji, Samoa, Philippines, West Africa, larvæ, apparently those of Filaria bancrofti, show no periodicity. In Fiji the usual intermediate host is Stegomyia pseudoscutellaris, a day-biting mosquito, so that possibly, as Bahr suggests, the mikrofilariæ have partly adapted themselves to the habits of their intermediate host, as the nocturnal mikrofilariæ are adapted for transmission by a nocturnal feeding mosquito, e.g., Culex fatigans, but how this could come about is a mystery. It is not certain in all cases whether the non-periodic mikrofilariæ really belong to Filaria bancrofti; some may be L. loa larvæ, or possibly unknown larvæ. An exact morphological description of these larvæ is therefore always necessary.

Preservation of Living Larvæ.--Blood from the vein (or finger puncture) is shaken up with twenty times its volume of sterile 0·9 per cent. salt solution, and kept in an ice cupboard (Fülleborn).

Concentration of Larvæ.--(a) The above mixture is hæmolysed with water and then sufficient salt solution added to make up to 0·9 per cent. The solution is allowed to stand or can be centrifugalized. (b) The blood is mixed with sodium citrate and centrifugalized; the larvæ are found in the leucocytic layer (Bahr). (c) Allow blood to clot in a small tube; the larvæ appear on the surface of the clot and are so got in pure serum. A drop of blood may also be allowed to clot on the slide; the larvæ are found in the clear areas of serum. (d) Hæmolyse blood with water or acetic acid. Centrifugalize, make smears from, or examine the sediment.

Removal of Red Corpuscles.--The blood film is allowed to stand for some minutes in a moist atmosphere. The staining solution is sucked through with blotting paper: the larvæ stick to the slide, while the corpuscles are washed out.

Morphology of Larvæ.--Wet staining: Azur II one part, 0·9 per cent., salt solution 3,000, or very dilute Giemsa or ripened methylene blue or neutral red solutions. Place a drop on the slide and add a drop of blood to this. The larvæ remain alive for one or more days; it sometimes takes twenty-four hours to stain some particular structure. Differentiation by drawing through weak eosin solution is often useful. This method is the best for finest details. The excretory pore, anal pore, excretory cell, and chief “genital” cell stain first, then the matrix cells and finally the column of nuclei.

Wet fixation and staining: The blood is spread on a large cover-glass--floated on the surface of 70 per cent. alcohol heated to about 70° C. Wash in water, (1) overstain with 1 in 1,000 azur II solution, warming slightly; (2) differentiate with (a) absolute alcohol (containing, if necessary, a trace of HCl), or (b) with absolute alcohol 96 per cent. ninety parts, anilin oil ten parts; (3) clear in origanum, bergamot or cajeput oil; (4) mount in balsam. Or stain with hæmatoxylin, e.g., Mayer’s glycerine alumhæmatein, heating till slightly steaming. Differentiate with acid (2 per cent. HCl) alcohol if overstained. Clear and mount as above.

Dry fixation and staining: (1) With azur II as above, or (2) with hæmatein (warm). Examine the dried films in the usual way without a cover-glass. The azur stains the excretory and genital cells clearly.

Thick films: (1) The blood is smeared out fairly thickly over an area as big as a sixpence.

(2) Dry quickly to prevent shrinking, using carefully a spirit lamp in a moist climate.

(3) Place films downwards in water for a few minutes.

(4) Fix in alcohol.

(5) Stain with azur II, 1 in 1,000. Differentiate as above. Examine as a dry film. This method suffices for showing the excretory cell and the G1 cell; or

(6) Stain with hæmatein (slightly steaming), especially for the column of nuclei and the sheath. The fixation in alcohol in this case may be omitted.

(7) The removal of the hæmoglobin and the fixation may be combined by using Ruge’s mixture (formalin 2 per cent., containing 1 per cent. acetic acid) or acetic alcohol (glacial acetic 1, alcohol 3).[303]

[303] [Acetic alcohol does well for detecting crescents in thick films of malaria blood.--J. W. W. S.]

Structure of Larvæ.--(1) Subcuticular cells: By vital staining, at intervals underneath the cuticle are seen a series of spindle-shaped cells--the subcuticular matrix cells of Rodenwaldt, the muscle cells of Fülleborn. There are thirty or forty or more of these.

(2) Nerve ring: Appears as a break in the nuclear column about 20 per cent. of total length from the head.

(3) Excretory system: Consists of a lateral spherical hollow excretory pore which shows a radial striation. Connected with the pore is an excretory cell which appears to be canalized. Excretory pore, 29·6 per cent. of length from head. Excretory cell, 30·6 per cent. of length from head.

(4) “Genital” cells and anal pore: Consists of a pore opening ventrally on a very fine papilla with which are connected four other cells in series, the chief “genital” cell (G1) being some distance from the three others, which lie close to the pore. G1, 70·6 per cent., anal pore, 82·4 per cent. of length from head.

(5) Internal body, viscus, or reserve material: Best shown by vital staining with neutral red. This is a granular strand-like body extending from 52·7 per cent. to 65 per cent. of length from head.

(6) Tail end: (i) Rod-like structures resembling those in the head, 90 per cent. of length. (ii) The column of nuclei extends to 95 per cent. of length, so that the terminal portion is free from nuclei.

(7) Mouth: Terminal according to some authors, lateral according to others. Some describe a fang on the head, others not. By vital staining and eosin differentiation two rod-like structures with mushroom-like caps can be seen behind the head.

(8) Cuticle: Transversely striated. There is a longitudinal break in the striation on each side corresponding to the lateral lines. The striation is best shown by vital staining with azur II and eosin differentiation.

(9) Column of nuclei: These nuclei of the gut cells form the main feature in ordinary dry films stained with hæmatoxylin. They are separated by a space from the subcuticular cells.

DISTINCTION BETWEEN Mikrofilaria bancrofti AND Mikroloa loa.

Dry Films, Hæmatoxylin Staining:--

Mf. bancrofti. Ml. loa.

(1) In graceful curves (but only (1) Kinked. if quickly dried). (2) Tip of tail free from nuclei. (2) Nuclei extend to tip. (3) Column of nuclei separated by (3) Not so distinctly. a space from the cuticle.

Azur Staining:--

(4) G1 cell small, easily overlooked. (4) G1 cell large, stains deep blue, cell protoplasm = twice width of larva, easily seen. (5) Excretory cell close to excretory (5) Excretory cell farther pore, 2 per cent. of length. from pore, 4 per cent. of length.

Vital Staining with Neutral Red:--

(6) Internal body or reserve material (6) Not shown. clearly shown.

Life History.--In the stomach of the mosquito the larvæ cast their sheath in the thickened blood in one to two hours. In twenty-four hours the majority have reached the thoracic muscles, where development proceeds. They are at first immobile and of a “sausage” form (110µ by 13 µ), with a short spiky tail. In three to five days the œsophagus is formed, the larva now being 0·5 mm. long. The larva appears to moult at this time. After the gut is formed papillæ, three or four in number, appear at the tail end. In two to three weeks the larvæ are 1·5 mm. long. They now leave the thorax and reach the labium, but they may be found in various parts of the body, e.g., the legs. They bore through Dutton’s membrane and so arrive on the surface of the skin, which they rapidly enter. Their development in man is unknown, but it may be very long, as children are not infected till 4 to 5, or even 10 years old, but this may be due to unknown causes.

Development takes place in numerous mosquitoes. Anophelines: Myzomyia rossii, Pyretophorus costalis, Myzorhynchus sinensis, Myzorhynchus barbirostris, Myzorhynchus peditæniatus.

Culicines: Culex pipiens, Culex fatigans, Culex skusei, Culex gelidus, Culex sitiens, Culex albopictus, Stegomyia fasciata, Stegomyia pseudoscutellaris, Stegomyia gracilis, Stegomyia perplexa, Mansonioides uniformis, Mansonioides annulipes, Scutomyia albolineata, Tæniorhynchus domesticus.

Partial development takes place in other species.

Pathology.--Among the conditions which Filaria bancrofti is believed to produce are lymphangitis, varicose glands, especially inguinal and epitrochlear, chyluria, chylocele, lymph scrotum, orchitis, abscess, and elephantiasis. The evidence that these so-called “filarial diseases” are produced by F. bancrofti is (1) geographical and statistical; (2) pathological. Bahr has contributed evidence of the former kind from his researches in Fiji, on which we may base the following statements:--

(1) The prevalence of filarial diseases is proportional to the prevalence of Mikrofilaria bancrofti in the blood. Thus in four villages examined by him he got the following figures:--

Village A Village B Village C Village D per cent. per cent. per cent. per cent. Mf. bancrofti 12·5 25 31 33 Filarial diseases 29 39 58 34 Total population 168 114 425 222

(2) Out of 257 people with Mf. bancrofti in the blood, 153 were suffering from filarial diseases, i.e., 59 per cent.

(3) Whereas of 672 people without Mf. bancrofti in the blood, only 263 were suffering from filarial diseases, i.e., 37·6 per cent.

(4) Again out of 416 people suffering from filarial disease, 153 showed Mf. bancrofti in their blood, i.e., 36·7 per cent.

It is generally assumed that all people suffering from filarial disease show at some (presumably early) stage larvæ in the blood; but we do not consider that this must necessarily be so. It appears to us quite possible that living adult filariæ may be present in the body, producing disease, without their larvæ appearing in the blood. The absence of larvæ from the blood in 63·3 per cent. of persons suffering from filarial disease is, however, generally explained otherwise. The adults which occur in enlarged glands, etc., get eventually destroyed by inflammatory reaction, so that larvæ are no longer being produced, while the enlarged gland, etc., which the adults have produced remains. This explanation assumes that the larvæ of the original worm die in the circulation or elsewhere, e.g., kidney, but we have no evidence as to the duration of life of larvæ in the human body; but also it assumes that a person cannot be reinfected with filaria, for otherwise there is no reason why the diseased should not be infected in the same proportion as the non-diseased. But assuming the explanation to be true, it would explain why a diseased population show larvæ in only about one-third of the cases. It must be borne in mind also that the figures are rather small.

Pathology.--In order to explain the effects which do or may be expected to occur from obstruction of lymphatics, it is necessary to have an accurate knowledge of the distribution and connections of lymphatic vessels (and glands) and the anastomoses of these vessels. We can only briefly summarize our knowledge here.

We should recall also that considerable destruction or obstruction of lymphatics or glands may occur without necessarily producing any lymphatic obstruction, at least, of a permanent nature, e.g., when a mass of lymphatic glands is destroyed by a bubo in the groin or, again, when a carcinomatous mass of glands is removed from the axilla. Again, to take the case of chyluria--where it is generally assumed that obstruction must occur higher up than the point at which the intestinal lacteals enter the juxta-aortic glands--this disease may occur, e.g., in temperate regions, quite apart from such obstruction. It is true that some of these cases of chyluria are not cases of chyle in the urine, but, as little or no fat is present, lymphuria. These do not require the above assumption, but seeing that true chyluria may apparently occur without such obstruction, we should be cautious about explaining this and other symptoms on the basis of obstructions which theory may demand, for only too often there are no post-mortem facts at our disposal.

Lymphangitis: What this is due to is unknown. There is no actual evidence of the occurrence of adults in the inflamed vessel. Complete disappearance, not to reappear, of (non-periodic) mikrofilariæ from the blood has been shown by Bahr and others to occur within twenty-four hours after an attack of lymphangitis, orchitis adenitis or simply a high temperature. This mysterious phenomenon requires explanation. If the mikrofilariæ were being killed by the attack, their dead bodies should still be found in the blood; or if the adults were being killed, for all we know to the contrary, the larvæ might well survive. We consider there is no evidence that either are affected, but that for some reason, as little understood as in periodicity, the larvæ now remain in the organs.

Abscess: In Fiji, by Bahr, they have been found in the substance of various muscles, e.g., quadriceps extensor, latissimus dorsi, serratus magnus, in the popliteal space, groin, axilla, and over the internal condyle of the humerus, and in the upper extremity they are frequently infected with cocci. They not infrequently contain fragments of dead adult filariæ. Their mode of origin is not clear. They form nearly 30 per cent. of cases of filariasis in Fiji. Of 95 cases, 41 showed mikrofilariæ in blood, 54 did not.

Hydrocele and enlarged testis: In Fiji they form about 10 per cent. (36 out of 343) of cases of filariasis. The fluid is usually sterile; mikrofilariæ were present in the fluid in 1 out of 11 cases. In the wall numerous calcified adult filariæ may be found. The walls consist chiefly of hypertrophied muscle with fibrous tissue, dilated blood-vessels and lymphatics, the lining epithelium of which appears to be absent; of 38 cases 14 had mikrofilariæ in the blood, 24 had not. Most of the cases are associated with elephantiasis of the scrotum (11 out of 12 cases).

Enlarged glands form over 40 per cent. (153 out of 343) of cases of filariasis, so that they are the commonest expression of filariasis met with in Fiji. The glands are enlarged, fibrotic, and the trabeculæ are thickened. The lymphatics are thickened or represented merely by fibrous tissue. The gland also shows dilated blood-vessels and numerous spaces filled with lymph. Giant-cells are common in those glands which contain remnants of filariæ. Masses of lymphocytes enclosed by inflammatory or fibrous tissue are common. Eosinophile cells are also extremely common, not only in the fibrous tissue of the glands, but in other inflammatory or fibrotic conditions: in other organs living or calcified filariæ are “usually” present. Only about 33 per cent. show mikrofilariæ in the blood. The epitrochlear gland is frequently enlarged in Fiji.

Breinl has examined enlarged glands and finds loose vascular fibrous tissue with lymphocytic invasion. In parts, the lymphocytes collect into areas 200 µ to 800 µ in diameter. The lymph tissue surrounding the spermatic cord showed abundance of vessels--(1) large, (2) small. The large had thick walls and wide lumina. In other cases the lumina were nearly filled by a thrombus of newly formed, fine, loose connective tissue.

Varicose glands: In about 7 per cent. (24 out of 343 cases) of filariasis, mikrofilariæ are found in the blood in 50 per cent. (12 out of 24).

Elephantiasis.--Elephantiasis scroti is associated with hydrocele in 50 per cent. of cases (12 out of 23); in 65 per cent. of cases (15 out of 23) there are associated enlarged glands in one or both groins, though also hydrocele and enlarged glands occur without elephantiasis scroti. In 13 out of 27, i.e., about 50 per cent., cases of elephantiasis in various regions, no associated enlargement of glands is found. Elephantiasis forms in Fiji less than 10 per cent. of cases of filariasis. Mikrofilariæ are present in the blood in 36 per cent. (12 out of 33) of cases.

Chyluria.--Exceedingly rare in Fiji. Theory would demand an obstruction above the point of entry of the lacteals, viz., the pre-aortic lymphatic glands, but in cases in temperate regions it may occur without any such lesion. In some of these cases the fluid is not chyle (fat absent), but presumably lymph. A discussion of the mode of production of chyluria, lymph scrotum, elephantiasis, etc., is at present premature; theory has far outrun fact. Too much stress had been laid on the mechanical action of the worms to the almost total exclusion of their (or possibly their larval) toxic action. The above analysis has been made in the hope of acquiring more extended observations similar to those made by Bahr.

Geographical Distribution.--Filaria bancrofti is known in nearly all tropical countries. It occurs in India, China, Indo-China, Japan, Australia, Queensland, the Islands of Polynesia (with the exception of the Sandwich Islands), Egypt, Algeria, Tunis, Madagascar, Zanzibar, Sudan, etc., the south of the United States of America, Brazil, the Antilles, etc. Whether it is the same species in all cases is questionable.

*Filaria demarquayi*, Manson, 1895.

Syn.: F. ozzardi, Manson, 1897.

The adult female F. demarquayi measures from 65 to 80 mm. in length by 0·21 to 0·25 mm. in breadth. The head has a diameter of from 0·09 to 0·1 mm. The mouth is terminal. The genital pore opens at 0·76 mm. from the head. The alimentary canal is nearly straight and terminates in an anus, which is subterminal. The opening of the anus is marked by a slight papilla. The tail is curved. It rapidly diminishes in size just below the anal papilla. A characteristic pair of fleshy papillæ project from the tip of the tail. The diameter near the tip of the tail before its termination is 0·03 mm. F. demarquayi is a thicker worm than Ac. perstans. It differs from F. bancrofti in the greater size of the head, in the smaller tail, and particularly in the marked fleshy papillæ at the tip of the tail. These papillæ are knobby, and not simply cuticular as in Ac. perstans.

The male of Filaria demarquayi has still to be found.

The adult female form of F. demarquayi was found by Dr. Galgey in the body of a native of St. Lucia in whose blood the larvæ had been found during life. Five adult females were found in the connective tissue of the mesentery.

The larva measures 200 µ in length by 5 µ in breadth; it is sharp-tailed, and has no sheath. Its movements are very active, and the absence of a sheath enables it to glide along freely all over the slide. It observes no periodicity, being present in the peripheral circulation both by day and by night. As a rule, some eight or ten parasites are found in an ordinary preparation. Sometimes hundreds of these larval filariæ may be counted on every slide.

The intermediate host has not been discovered.

Geographical Distribution.--St. Vincent, Dominica, Trinidad, and St. Lucia (West Indies), British Guiana, New Guinea (?).

*Filaria taniguchi*, Penel, 1905.

Female 68 by 0·2 mm. in breadth. Cuticle non-striated. Mouth two pairs of papillæ. Anus 23 mm. from extremity. Vulva 1·3 mm. from mouth. Larva 164 µ by 8 µ, sheathed. Tail truncated. Periodicity nocturnal.

Habitat.--Lymphatic glands of man. Japan.

*Filaria (?) conjunctivæ*, Addario, 1885.

Syn.: Filaria peritonei hominis, Babes, 1880; Filaria inermis, Grassi, 1887; Filaria apapillocephata, Condorelli-Francaviglia, 1892.

The female only of this species is known. It measures 16 to 20 cm. in length and 0·5 mm. in breadth, and is of a whitish or brownish tint. The cuticle is striated with fine transverse and more marked longitudinal striæ with the exception of a small field surrounding the mouth, which is terminal and has neither papillæ nor lips. The œsophagus measures 0·6 mm. in length. The anus is 3 mm. in front of the rounded posterior extremity, and behind it there are two (glandular?) sacs. The vulva is close behind the oral aperture; the vagina soon divides into two convoluted uteri, which are filled with eggs and embryos. Embryos 350 µ by 5·5 µ.

This species (115 mm. long) was first observed in Milan by Dubini in the eye of a man; subsequently it was observed, encysted and calcified (190 mm. long), by Babes in the gastro-splenic omentum of a woman in Budapest, and finally one (95 mm. long) was extracted by Vadela from a tumour the size of a pea in the ocular conjunctiva of a woman in Catania (Sicily), which case has been described by Addario. Possibly Agamofilaria palpebralis, Pace, 1867 (nec Wilson, 1844), and A. oculi humani, v. Nordm., 1832, are the same species.

Filaria (?) conjunctivæ is certainly only an incidental parasite of man; the horse and ass are its normal hosts, but it is not common in these animals, or is frequently confused with Hamularia equi, Gmelin, 1789.

Group. *Agamofilaria*, Stiles, 1906.

Not a generic but a group name for immature Filariidæ the development of which does not admit of generic determination.

*Agamofilaria georgiana.*

Adult unknown, length from 32 to 53 mm. Maximum diameter 560 µ to 640 µ. Head no cephalic cone. Mouth small, circular, surrounded by six papillæ (two small latero-median and four sub-median). The larger papillæ are 24 µ from base to tip. Excretory pore about 0·5 mm. from head. Anus 64 µ to 128 µ from tip. Cuticle fine striæ near anus, occasionally elsewhere. Lateral lines clearly marked. Œsophagus 2·5 to 2·9 mm. Rectum 200 µ long.

Habitat.--Superficial sores on the ankle of a negress, Georgia, U.S.A.

*Agamofilaria palpebralis*, Pace, 1867 (nec Wilson, 1844).

100 by 1·5 mm., removed from a cyst in the left upper eyelid of a boy by Pace, in Palermo.

*Agamofilaria oculi humani*, v. Nordmann, 1832.

Syn.: Filaria lentis, Diesing, 1851.

The sexless Nematodes observed in the lens of the human eye were termed Filaria oculi humani. Only three cases are known. v. Nordmann observed very small round worms in the lens of a man and woman with cataract, and Gescheidt once found three specimens in the lens of a woman similarly affected.

The demonstration of nematode-like formations in the vitreous remains uncertain even when movements are observed, and when they cannot be extracted and examined microscopically the doubt may occur that one may have mistaken the remains of the hyaloid artery for a worm, which it resembles in form, size and colour; the slightest movement of the eye also causes it to move so that it simulates a living organism.

Accordingly it would be more correct to exclude all the cases known only ophthalmoscopically (Quadri, 1857; Fano, 1868; Schoeler, 1875; Eversbusch, 1891). There then remains only one positive case, described by Kühnt in 1891. In this case it was possible to follow the gradual growth of the parasite for some time, and the worm, which measured only 0·38 mm. in length, was finally extracted.

*Agamofilaria labialis*, Pane, 1864.

The parasite measures 30 mm. in length; the anterior extremity is pointed; the terminal oral aperture is surrounded by four papillæ; the anus opens 0·5 mm. in front of the posterior extremity; the vulva is 2·5 mm. in front of the anus; the uterus is double; the anterior one passes with convolutions forward to the cephalic end; the posterior one is directed backwards and remains rudimentary.

Extracted from a small pustule on the inner surface of the upper lip. Also found in Naples by Pierantoni in 1908.

The position of many of these worms is doubtful, and still more so is that of many other imperfectly described “Filariæ,” which are hardly more than useless and confusing names. These include the following:--

*Filaria (?) romanorum-orientalis*, Sarcani, 1888.

Observed in the blood of a Roumanian woman; 1 mm. in length, 0·03 mm. in breadth; tail end pointed, a tongue-like appendage on the head. Eggs the size of a red cell with developed embryo, apparently viviparous.

*Filaria (?) kilimaræ*, Kolb, 1898.

Several female specimens, 10 to 20 cm. long by 0·5 to 1 mm. broad, were once found free in the abdomen of a fallen Kitú warrior; according to Spengel, who examined them, the oral papillæ of these worms were similar to those of Dracunculus medinensis. Moreover, Kolb classifies together Nematodes that probably have no connection with each other.

*Filaria (?) sp.?*

Cholodkowsky calls attention to Filariæ that are still unknown which cause tumours resembling whitlows on the fingers of peasants of the Twer Government.

Mikrofilaria powelli, Penel, 1905. In Bombay.

Mikrofilaria philippinensis, Ashburn and Craig, 1906. In the Philippines.

Genus. *Setaria*, Viborg, 1795.

Syn.: Hamularia, Treutler, 1793; Tentacularia, Zeder, 1800 (nec Bosc, 1797).

Mouth with projecting peribuccal armature deeply notched on the lateral margins, less so dorsally and ventrally. Tail in both sexes with peculiar caudal appendages.

Parasitic in serous cavities, especially of ruminants.

*Setaria equina*, Abildg., 1789.

Syn.: Gordius equinus, Abildg., 1789; Filaria equi, Gmelin, 1789; Hamularia lymphatica, Treutler, 1793; Tentacularia subcompressa, Zedder, 1800; Filaria papillosa, Rud., 1802; Filaria hominis bronchialis, Rud., 1819; Filaria hominis, Dies., 1851; Strongylus bronchialis, Cobb., 1879.

The body is whitish, filiform, pointed posteriorly. The cuticle presents a delicate transverse striation. The mouth is small, round, and surrounded by a chitinous ring, the border of which carries, at the sides, two semilunar lips, and there is on the dorsal as well as on the ventral surface a papilliform process; on the tail, corresponding with each sub-median line, is a conical papilla. The male measures 6 to 8 cm. in length; the posterior extremity ends in a corkscrew spiral; there are on each side four pairs of pre-anal and four or five post-anal papillæ; the spicules are unequal. The female measures 9 to 12 cm. in length and is viviparous; the embryos measure 0·28 mm. in length and 0·007 mm. in breadth.

Setaria equina is a frequent parasite of horses and asses; it inhabits the peritoneal cavity, and from there occasionally invades the female genitalia or even the liver; it is found more rarely in the pleural cavity or in the cranium. The statement that it also occurs in the subcutaneous connective tissue is probably due to confusion with Setaria (Filaria) hæmorrhagica, Raill., 1885 (Filaria multipapillosa, Cond. et Drouilly, 1878). Setaria labiata papillosa (immature form) occurs in the eye of the horse, adults in the peritoneal cavity.

Treutler, in 1790, found a filaria in the enlarged bronchial lymphatic gland of a patient suffering from phthisis. It measured 26 mm. in length and had two spicules, which Treutler mistook for mouth hooks, hence the name Hamularia. Blanchard mentions another case from Geneva, Brera a third and v. Linstow a fourth. As shown by the synonyms, a few authors consider this form to be a distinct species, which is hardly probable.

Genus. *Loa*, Stiles, 1905.

Characterized by the possession of cuticular bosses in both sexes (fig. 294).

*Loa loa*, Guyot, 1778.

Syn.: Filaria oculi, Gerv. et v. Ben., 1859; Dracunculus oculi, Diesing, 1860; Dracunculus loa, Cobbold, 1864; Filaria subconjunctivalis, Guyon, 1864.

The male measures 25 to 35 mm. in length, and 0·3 to 0·4 mm. in breadth; the cuticle is not striated, but, with the exception of the anterior and posterior extremities (1·5 mm.), is beset with numerous irregularly distributed bosses (4 µ to 12 µ high by 12 µ to 27 µ broad). The anterior extremity is somewhat attenuated, and in front is conical and transversely truncated. At the anterior limit of the conical part is a small papilla corresponding with the dorsal and ventral median lines, and a little in front six non-projecting sensory papillæ (two lateral, four sub-median). Excretory pore 0·65 mm. from the anterior end. The posterior extremity is attenuated and somewhat curved ventrally; the anus is 0·082 mm. distant from the rounded posterior border. In front of the anus on each side are three globular and pedunculated papillæ of different sizes, set close one behind the other but asymmetrically; behind the anus on either side are two smaller papillæ of a different shape; the anterior one resembles the pre-anal papillæ in form, but is smaller; the posterior one is conical, and rests with a broad base on the cuticle. The spicules are 0·113 and 0·176 mm. long.

The female measures 45 to 63 mm. in length by 0·5 mm. in breadth. It is also beset with irregularly distributed bosses, which in places lie close to each other, and extend to the anterior extremity; posteriorly they become less frequent, but are not entirely absent. The anterior extremity is conical, the posterior one straight, attenuated, rounded off, 0·17 mm. from the anus. The uteri contain eggs in the most various stages of development, as well as hatched-out larvæ, 253 µ to 262 µ in length and 4·7 µ to 5 µ in breadth. The vulva lies about 2 mm. from the head end. The vagina, 9 mm. long, divides into two branches, which at first run posteriorly and parallel to one another for about 18 mm. One then bends forward, runs as far as the œsophagus, bends here again and runs backward to end at the point of its first bending. The other branch at first runs straight backward and then bends forward, but before reaching the point of the first bend of the anterior tube bends backward again, forms again a loop and ends at the level of the anus. The tubes consist in the main of the uterus, then a club-shaped swelling, the receptaculum seminis, then the oviduct 2 mm. long, and finally the ovary.

Unsegmented eggs measure 32 µ by 17 µ, in the morula stage 40 µ by 25 µ, and when containing embryos 50 µ by 25 µ. The vitelline “shell” of the egg is, according to most authors, stretched by the embryo and becomes the sheath of the hatched larva. While still in the vulva, the larva measures 217 µ to 274 µ (average 246 µ) in fresh, 146 to 226 µ (average 192 µ) stained.

Site of Worms.--In various localities; under the muscular aponeuroses on extensor surfaces of arms and legs, fingers, trunk, eyelid, conjunctiva, frænum linguæ, penis, pericardium, anterior chamber of eye, and, according to some authorities, in lymphatic vessels, e.g., those of spermatic cord. As many as thirty adults may be found. The worms appear to be frequently immature, and it has been stated that worms in superficial parts are immature, those situated deeply are mature, but the data are few.

The first accounts of Loa loa--long since forgotten--were reported by Pigafetta, and are contained in a book of travels on the Congo printed in 1598. In an accompanying illustration is depicted, not only the ancient method of extraction of the Medina worm, but also the operative removal of the filaria from the conjunctiva. Subsequently the presence of the worm in negroes was confirmed by Bajon in Guiana (1768) and by Mongin in Mariborou (San Domingo), likewise in a negro (1770). At about this time a French ship’s doctor, Guyot, was cruising on the West Coast of Africa; he observed the parasite termed “loa” by the natives, and learned that it was frequent in the negroes of the Congo district. Since that time numerous observations have been reported. It was formerly common in South America, where the parasite was imported by slaves, but it disappeared when the traffic ceased; it was particularly prevalent in the Congo, where it occurs not only in natives, but also in Europeans. During recent times it has repeatedly been observed in Europe in negroes as well as in white men who have lived on the West Coast of Africa.

Nematodes of different size have been repeatedly observed in the eye of man, in the anterior chamber, lens and vitreous. For example, Mercier, in 1771 and 1774, removed a filaria out of the anterior chamber of two negroes in St. Domingo. One was 36 mm. long. Barkan, in 1876, in San Francisco, removed one from the eye of an Australian. Again, Cappez and Lacompte, in Brussels, in 1894, observed for some weeks immature Nematodes in the eye of a negro girl, aged 2-1/2 years, and then removed them. What these Nematodes actually were in these cases it is impossible to say.

Structure of Larvæ.--In dried films the larva varies in size from 140·5 µ to 166·5 µ, average, 152·5 µ; while another set of measurements gave the values 131 µ, to 150 µ, average, 143·6. In films fixed with hot alcohol the dimensions were 208 µ to 254 µ, average, 231 µ.

The nerve ring 21·4 to 21·8 per cent. Excretory pore 30·4 to 31·8 per cent. Excretory cell 34·8 to 37·3 per cent. G1 cell 68·2 to 68·5 per cent. Anal pore 81·6 to 82·4 per cent. of total length. For other details cf. Filaria bancrofti.

Larvæ in Blood.--These from their diurnal periodicity are known as Mikrofilaria diurna. The evidence that these larvæ are the young of the adult worm Loa loa is: (1) They are identical in structure with larvæ taken from the uterus of L. loa; (2) their geographical distribution is the same as that of L. loa; (3) they eventually occur in the blood of patients suffering from Calabar swellings, a condition due to L. loa. Their occurrence in the blood in this latter condition and in L. loa infections we shall consider later.

Periodicity.--Here, as in the case of the larvæ of Filaria bancrofti, the larvæ that appear in the blood are probably the overflow simply of the larvæ which we assume, on analogy, to have their principal site in the lungs. They appear in the blood about the time of getting up, 6 to 8 a.m. (10 in 20 mm.^3), at 12 noon there are twenty-four, at 8 p.m. the number has fallen to eighteen, and at midnight to one, while from 2 a.m. to 6 a.m. none, or one only, may be found. This periodicity is, as a rule, a very constant one, but there are exceptions, and in certain cases more have been found at midnight than at 9 a.m. The periodicity is also lost in pathological conditions, e.g., sleeping sickness (vide also under Filaria bancrofti). The possibility of non-periodic Loa loa larvæ should also be considered.

Pathology.--The parasite wanders about the body, and may be seen under the skin in thin parts. Their advance is in some cases at the rate of an inch in two minutes. During their progress they give rise to creeping sensations and to a condition of transient œdematous areas known as Calabar swellings on various parts of the body, e.g., arm. These vary in diameter from 1 to 10 cm., and often shift their position an inch or so a day. They give rise to a certain amount of redness, tension and heat, and their development is promoted by muscular action of the part. They disappear to reappear elsewhere. The condition is associated with a high eosinophilia, 50 per cent. being not uncommon. Patients known to harbour L. loa, e.g., native children, frequently show no larvæ in their blood, but they may do so after years of infection. Again, in patients having an infection of Mikrofilaria diurna, there is frequently at the time no evidence of the presence of Loa loa adults. Here again they may appear later, but the conditions which determine whether persons infected with L. loa show larvæ in the blood, or persons infected with Mikrofilaria diurna also show L. loa, are unknown, though explanations unsupported by facts abound. Likewise also the mode of production of the swellings is unknown.

Not uncommonly Mikrofilaria perstans occurs in the blood together with M. diurna.

Duration of Life.--This is long, as some cases have been observed five to six years after leaving Africa. The incubation period is about a year.

Life-history.--Development of the larvæ takes place in the salivary glands of Chrysops sp. as shown by Leiper.

Geographical Distribution.-- West Africa, especially in Congo.

Genus. *Acanthocheilonema*, Cobbold, 1870.

Cuticle striated longitudinally. Œsophagus divided into two portions. Tail in both sexes with short lateral conical cuticular appendages. Spicules unequal, the larger membranous distally, the smaller hooked. Vulva in œsophageal region.

*Acanthocheilonema perstans*, Manson, 1891.

Syn.: Filaria perstans, P. Manson, 1891; Filaria sanguinis hominis var. minor, Manson, 1891.

The adult female Ac. perstans measures 70 to 80 mm. in length by 120 µ to 140 µ in breadth. The head is club-shaped and measures 0·07 mm. in diameter. The vulva opens at 0·6 to 1·0 mm. from the head. The tail is curved and presents a cuticular thickening which forms two triangular appendages. The anus opens at the apex of a papilla situated in the concavity of the curve formed by the tail 150 µ from the end. The diameter of the tail just before termination is 0·02 mm.

The adult male measures 45 mm. in length by 60 µ to 80 µ in breadth. The diameter of the head is 0·04 mm. The tail is much curved. There are four pairs of pre-anal papillæ and two pairs of post-anal papillæ. Spicules very unequal in size. Cloaca 121 µ from the tail end. At the tail end two triangular cuticular appendages.

The adult worms inhabit the connective tissue at the base of the mesentery, especially in the region of the pancreas, abdominal aorta and suprarenals. To find them the mesentery should be removed, placed in a 2 per cent. solution of formalin, and then carefully examined at leisure.

Mikrofilaria perstans.--160 µ to 210 µ by 5 µ to 6 µ broad. Has no sheath. Cuticle transversely striated. Tail rounded off, not pointed. Nerve ring at 34 µ. Excretory pore 49 µ, genital pore 125 µ from head. Smaller larvæ 90 µ to 110 µ by 4 µ broad. A “fang” is also described on the head.

Mf. perstans. Mf. demarquayi. (1) Tail stumpy. (1) Tail pointed. (2) Column of nuclei extends to (2) Does not extend to tip. tip of tail.

Periodicity.--None.

Life-history.--Unknown.

Geographical Distribution.--Very common in many parts of Africa: Sierra Leone, Dahomey, Northern Nigeria, Southern Nigeria, Cameroons, Ivory Coast, Gold Coast, Old Calabar, Congo, Uganda. Absent from Zululand, Basutoland. On the East Coast of Africa it is not found in the towns of Zanzibar and Mombasa, neither is it found in the country of the Masi, nor amongst the Kavirondo, who dwell along the north-east shores of Lake Victoria.

In South America, Ac. perstans is very common amongst the aboriginal Indians in the interior of British Guiana. However, it is not found in Georgetown and in New Amsterdam, neither is it found in the cultivated strip of coast lying between these two towns, but it is common on the coast farther north near the Venezuelan boundary, where the forests stretch to the sea. The Waran Indians, who live at the mouth of the Waini river, harbour this parasite. It is absent in the West Indies.

Topographically, Ac. perstans is found only in areas covered by dense forest growth and abounding in swamps. In Kavirondo, where the forest disappears and the land is covered with scrub and short grass, it is not found; likewise it is not found on the grassy plains of the highlands of British East Africa. Towns and cultivated areas are free from it.

Genus. *Dirofilaria.* Railliet and Henry, 1911.

Body very long, thread-like, cuticle transversely striated. Mouth with six papillæ. Male tail spiral with voluminous pre-anal and some large post-anal papillæ; spicules unequal. Vulva near the anterior hundredth of body; viviparous. Parasitic in heart or blood-vessels and subcutaneous tissue.

*Dirofilaria magalhãesi*, R. Blanchard, 1895.

Syn.: Filaria bancrofti, v. Linstow, 1892; Filaria bancrofti, P. S. de Magalhães, 1892 (nec Cobbold, 1877).

The male measures 83 mm. in length by 0·28 to 0·40 mm. in breadth. The anterior extremity is rounded, and has no papillæ (?6); the posterior extremity exhibits a double curve, with four pre-anal and four post-anal papillæ on each side. These are large and have a villous appearance. The mouth is round and unarmed, the pharynx measures 1 mm. in length, is cylindrical, very muscular, and its hinder part is dilated. The anus is situated 0·11 mm. in front of the hind end. There are probably two unequal spicules; one only, however, is known--apparently the shorter one--the length of which is given as 0·17 to 0·23 mm.

The female measures 155 mm. in length and 0·6 to 0·8 mm. in breadth; the rings of the cuticle are 0·005 mm. apart (in the male 0·003 mm. apart); the anterior extremity is slightly thickened and club-like, the posterior extremity is slender, and terminates obtusely; the lateral line is 0·127 mm. in breadth (that of the male 0·007 to 0·008 mm.); the anus opens 0·13 mm. in front of the hind end, the vulva is 2·5 mm. distant from the mouth, the ovaries are two much convoluted tubes. The eggs measure 38 µ by 11 µ.

This species was first discovered at a post-mortem, in the left ventricle, by J. P. Figueira de Saboia in Rio de Janeiro, and has been described by P. S. de Magalhães.

D. immitis occurs in the right ventricle of the heart of the dog in Europe and the Tropics.

D. repens is also a common subcutaneous Nematode in dogs in Annam.

Sub-family. *Onchocercinæ*, Leiper, 1911.

Cuticle with spiral thickenings.

Genus. *Onchocerca*, Diesing, 1841.

Male with four pre-anal papillæ. Female with vulva situated anteriorly.

*Onchocerca volvulus*, R. Leuckart, 1893.

Syn.: Filaria volvulus, R. Leuckart, 1893.

The adult male measures 30 to 35 mm. in length by 0·14 mm. in breadth. The body is white, filiform, attenuated at both ends. The head is rounded and has a diameter of 0·048 mm. The cuticle is distinctly transversely striated. The mouth is unarmed. The alimentary canal is straight, the anus opening 0·07 mm. from the tip of the tail. The tail is strongly curved and somewhat flattened on the concave surface. There are three papillæ, one large and two small, on each side of the cloaca and one large and two post-anal small papillæ. Two curved spicules, 0·166 and 0·08 mm. respectively.

The adult female is of uncertain length, but much longer than the male, probably about 10 to 12 cm. The head is rounded and truncated; it measures 0·065 mm. in diameter. The tail is curved. The vulva opens 0·55 mm. from the head. The hand-like cuticular thickenings are well marked. Eggs ovoid with a prolongation at each pole “like an orange wrapped in tissue paper.” The larva measures about 300 µ by 7 µ to 8 µ; it has no “sheath.” The body tapers from about the last fifth of its length, and terminates in a sharply pointed tail. At about the anterior fifth of the body there is a *V* spot.

O. volvulus is found in peculiar subcutaneous tumours, the size of a pea to that of a pigeon’s egg. The same patient may present one or several of these tumours. The regions of the body most frequently affected are those in which the peripheral lymphatics converge. Thus they are usually found in the axilla, in the popliteal space, about the elbow, in the sub-occipital region and in the intercostal spaces. The tumours are never adherent to the surrounding structures, and can be easily enucleated. They are formed of a dense connective tissue wall and internally a looser fibrous meshwork. This is traversed by a series of canals in which the worms lie, but they are also partly embedded in the denser wall. The canals apparently dilate into cavities filled with slimy pus-like fluid consisting largely of larvæ. According to Brumpt the posterior extremity of the male, and the anterior extremity of the female with its vaginal opening, are free in one of the spaces for the purpose of copulation and parturition. If a tumour be cut into and placed in salt solution, Rodenwaldt states that the undamaged males wander out into the solution.

The formation of the tumours is elucidated by Labadie-Lagrave and Deguy’s case. The authors found an immature female Onchocerca volvulus in a lymphatic vessel partly obstructed by an infiltration of fibrin and leucocytes. It appears, therefore, that the presence of the parasites within the lymphatics gives rise to an inflammatory process, and that the consequent fibrinous deposit envelops the parasites, obliterates the lumen of the vessel, and ultimately isolates the affected tract. At any rate, in young tumours the worms appear to lie in a structureless substance permeated by leucocytes in which connective tissue is gradually organized from the periphery, thus isolating the worms.

In cases of infection with O. volvulus larvæ have been found by Ouizilleau, Fülleborn, and Simon in lymph glands, and in the finger blood if considerable pressure is used so as to squeeze lymph out of the tissues. They are sheathless, and the following are the dimensions in ordinary dried films: Length, 274 µ; nerve ring, 23·7 per cent.; G1 cell, 69·6 per cent.; end of last tail cell, 96·3 per cent. The dimensions of larvæ of O. volvulus taken from the uterus and prepared in the same way are: Length, 224·5 µ; nerve ring, 24·3 per cent.; G1 cell, 68·9 per cent.; end of the last tail cell, 95·5 per cent. In all probability the larvæ in the glands and blood are those of O. volvulus.

According to the natives, the tumours may last indefinitely and never ulcerate. Some old patients told Brumpt that their tumours had been present since childhood. Probably Onchocerca volvulus, like some other Filariidæ, may live for many years.

O. volvulus occurs in various parts of West Africa: Gold Coast, Sierra Leone, Dahomey, Lagos, Cameroons. Brumpt, on the banks of the Welle between Dongon and M’Binia (Belgian Congo), found about 5 per cent. of the riverine population affected.

Family. *Trichinellidæ*, Stiles and Crane, 1910.

Sub-family. *Trichurinæ*, Ransom, 1911.

Male with a single long spicule, with sleeve-like sheath. One ovary. Eggs with an opening at each pole closed by a plug-like operculum. Eggs hatch on being swallowed by a new host. Genera: Trichuris, Capillaria.

Genus. *Trichuris*, Röderer and Wagler, 1761.

Syn.: Trichocephalus, Goeze, 1782 (nec Trichiurus, L., 1758); Mastigodes, Zeder, 1803.

The anterior part of the body is very long and thread-like; the posterior, much shorter part, is thicker, rounded posteriorly, and the anus is terminal. The males have the posterior extremity spirally rolled; the vulva is situated at the commencement of the posterior part of the body. The Trichocephali live in the large intestine of mammals, the cæcum by predilection; their development is direct, infection occurs through the ingestion of embryo-containing eggs.

*Trichuris trichiura*, Linnæus, 1761.

Syn.: Trichocephalus trichiurus, L., 1771; Ascaris trichiura, L., 1771; Trichocephalus hominis, Schrank, 1788; Trichocephalus dispar, Rud., 1801.

The male measures 40 to 45 mm. in length, the spicule is 2·5 mm. long, its retractile sheath is beset with spines. The female measures 45 to 50 mm. in length, of which two-fifths appertain to the posterior part of the body. The ova are barrel-shaped and have a thick brownish shell which is perforated at the poles. Each opening is closed by a light-coloured plug. The eggs measure 50 µ to 54 µ in length and 23 µ in breadth; they are deposited before segmentation. Trichuris trichiura usually lives in the cæcum of man, and is also occasionally found in the vermiform appendix and in the colon, exceptionally also in the small intestine; usually only a few specimens are present, and these do not cause any particular disturbance, although, as Askanazy found, they feed on blood; in other cases cerebral symptoms of more or less severity are observed when Trichocephali are present in large numbers. At post-mortems performed soon after death the filiform anterior extremity of the worm is frequently found embedded in the mucous membrane (Askanazy).

The whip worm is one of the most common parasites of man and appears to be distributed over the entire surface of the globe; it is, however, more frequent in the warmer regions. It is found in persons of both sexes and all ages with the exception of infants. In autopsies it is found in the following numbers: In Dresden in 2·5 per cent., in Erlangen in 11·1 per cent., in Kiel in 31·8 per cent., in Munich in 9·3 per cent., in Petrograd in 0·18 per cent., in Göttingen in 46·1 per cent., in Basle in 23·7 per cent., in Greenwich in 68 per cent., in Dublin in 89 per cent., in Paris in about 50 per cent., and in Southern Italy in almost 100 per cent. On examining the fæces the eggs of the whip worm were found as follows: In Munich in 8·26 per cent., in Kiel in 45·2 per cent., in Greifswald in 45 per cent., in North Holland in 7 per cent., in Novgorod in 26·4 per cent., in Petrograd in 5 per cent., in Moscow in 5·3 per cent.

The development of the eggs is completed in water or in moist soil, and occupies a longer or shorter time according to the season; the eggs possess great powers of resistance, as do the larvæ, which, according to Davaine, may remain as long as five years in the eggshell without losing their vitality. Leuckart proved by experiment that direct infection with Trichuris ovis (Ovis aries) and T. crenata (Sus scrofa dom.) was produced by embryo-containing eggs; Railliet obtained the same results with T. depressiuscula of dogs, and Grassi subsequently, by means of two experiments, demonstrated the direct development of Trichuris trichiura. In one case embryo-containing eggs were swallowed on June 27, 1884, and on July 24 the ova of Trichocephali were found in the fæces for the first time.

Trichuris trichiura is found not only in man, but also in various monkeys (T. palæformis, Rud.), as well as in lemurs (T. lemuris, Rud.).

Other species are T. crenata in pig; T. ovis in cattle, sheep, goat, and pig (?); T. depressiuscula in dog; T. campanula in cat; T. unguiculata in rabbit and hare; T. cameli in camel; T. discolor in humped cattle; T. nodosus in mouse; T. alcocki in the thamin (India); T. globulosa in camel; T. giraffæ in giraffe.

Sub-family. *Trichinellinæ*, Ransom, 1911.

Male without spicule; females ovoviviparous. Larvæ penetrate muscles of host and become encysted. Genus: Trichinella.

Genus. *Trichinella*, Railliet, 1895.

Syn.: Trichina, Owen, 1835 (nec Meigen, 1830).

Very small Trichinellinæ, the males of which have two conical appendages at the caudal extremity; the vulva is situated at the border of the anterior fifth of the body. There is only one species.

*Trichinella spiralis*, Owen, 1835.

Syn.: Trichina spiralis, Owen, 1835.

The male measures 1·4 to 1·6 mm. in length and 0·04 mm. in diameter. The anterior part of the body is narrowed, the orifice of the cloaca is terminal and lies between the two caudal appendages; internal to these are two pairs of papillæ, dorsal one behind the other. The cloaca is evertible for copulation. The females measure 3 to 4 mm. in length and 0·06 mm. in diameter; anus terminal.

Trichinella spiralis in its adult stage inhabits the small intestine of man, pig, wild boar, rat. The young do not leave the body of the host but become encysted in the muscles. Experimentally it develops in the black rat (Mus rattus), the sewer rat (M. decumanus), the domestic pig (Sus scrofa dom.), the wild boar (Sus scrofa ferox), the domestic dog (Canis familiaris), the fox (C. vulpes) the badger (Meles taxus), the polecat (Putorius fœtidus), the marten (Mustela foina), the raccoon (Procyon lotor), the hippopotamus and the cat, and many other mammals (rodents and carnivora); Trichinellæ have been artificially introduced, by administering the encysted stage, into the dog, the mole (Talpa europæa), the mouse (Mus musculus), the hare (Lepus timidus), the rabbit (L. cuniculus), the hedgehog (Erinaceus europæus), the marmot (Cricetus vulgaris), the vole, the dormouse, the sheep, the calf, the horse, etc. Human beings and the pig, rat, mouse, guinea-pig and rabbit are most easily infected; less easily the sheep, calf and horse; with difficulty the cat, dog and badger. Trichinella can also be reared in birds (fowl, pigeon and duck), but the young do not encyst in the muscular system, but are expelled with the fæces. By cold-blooded animals as well as by insects (Calliphora vomitaria), encysted Trichinellæ are evacuated without undergoing any change, but they will still develop if subsequently ingested, say, by rabbits. According to Gujon, however, Trichinella can develop in salamanders, because he has found Trichinella of the muscles in these animals after they had been fed on encysted specimens. A high temperature (30°C.) must be provided in which to keep the experimental animals to ensure the success of the infection.

History.--Encapsuled Trichinellæ had been observed in London by Peacock (1828) and by J. Hilton (1833) in the muscular system of man; soon after (1835), Paget found them in London in an Italian who had died of tuberculosis, and recognized them to be encysted entozoa, which R. Owen described as Trichina spiralis. Soon after, some further observations were reported on the occurrence of encysted Trichinellæ, in man, in England, Berlin, Heidelberg, Denmark, North America; they were also found in the pig (Leidy, Philadelphia) and the cat (Herbst, Göttingen, and Gurlt, Berlin). Herbst even succeeded in infecting a badger with encysted Trichinellæ, and subsequently infected two dogs with the flesh of this badger (1850). In 1855 R. Leuckart (Giessen) also commenced feeding experiments, and, like Küchenmeister and Virchow (1859), first went on the wrong track because it was believed at that time that Trichinellæ were the larvæ either of Trichocephalus or Strongylus. Nevertheless, these experiments yielded some important results; they showed that Trichinellæ become adult in the intestine within a few days, and that the females are viviparous (Leuckart). Until that time Trichinellæ had been regarded as fairly harmless guests of man, but opinions soon changed when Zenker in Dresden (January, 1860), in performing the autopsy of a girl, aged 10, who had entered the hospital with typhoid symptoms and there died, found Trichinellæ (not yet encysted) in the muscles; the intestinal lesions characteristic of typhoid were lacking, but numerous adult Trichinellæ were found in the intestine. Inquiries elicited the fact that at about Christmas time the girl had been taken ill after eating pork, and at the same time the butcher from whom the meat was bought as well as several of his customers fell sick: the pickled pieces of the same meat were full of Trichinellæ. In the face of this information it was not difficult to ascertain the cause of the disease and the manner of infection in Zenker’s case, and it was not long before Leuckart, Virchow and Zenker were able by renewed experiments to demonstrate the cycle of development of Trichinella spiralis. Similar investigations followed by Claus in Würzburg, Davaine in Paris, Fuchs and Pagenstecher in Heidelberg, etc.

Hardly had Zenker’s case been published than numerous observations on trichinosis in man appeared, some referring to isolated cases, others to small or great epidemics, and nearly all from North Germany. The worst epidemic was that of Hadersleben (1865), in which place, numbering hardly 2,000 inhabitants, 337 persons were taken ill within a short time, and of these 101 died. The source of infection proved to be a single pig, the flesh of which had been mixed with that of three other pigs; 200 of the badly infected persons had exclusively eaten raw pork.

Moreover, it soon became clear that epidemics of trichinosis had been observed in Germany prior to 1860, but that their nature had not been recognized, although in a few cases Trichinellæ had been found in the muscles of those who had succumbed.

HISTORY OF THE DEVELOPMENT OF Trichinella spiralis.

Shortly after their introduction into the intestine of experimental animals the encysted Trichinellæ escape from their capsules, which are destroyed by the gastric juices, and they then enter the duodenum and jejunum, where they become adult. During this period they do not grow much, the males from 0·8 to 1·0 to 1·2 to 1·5 mm.; the females to 1·5 to 1·8 mm. Soon after copulation, which takes place in the course of two days, the males die; the females, which during the following days attain a length of 3 to 3·5 mm., either bore more or less deeply into the villi or, by means of Lieberkühn’s glands, into the mucous membrane (Askanazy, Cerfontaine, Geisse), and thus usually attain the lymph spaces. A few also pierce the intestinal wall and are then found in the mesentery and glands. The females deposit their young, the number of which, according to Leuckart, averages at least 1,500, in the lymph spaces; the newly born larvæ measure 90 µ to 100 µ in length, 6 µ in diameter, and they do not appear to increase in size during their migrations. The migrations are mostly passive, that is to say, the larvæ are carried along mainly by the lymph stream to the heart, but sometimes they are active, as may be inferred from the fact that young Trichinellæ are found in various parts of the intestinal wall beyond the chyle and lymph spaces, as well as in abundance in the abdominal cavity. Trichinellæ occur in the heart’s blood of artificially infected animals seven to twenty-three days after infection. If scanty, dilute the blood with about ten times the amount of 3 per cent. acetic acid and centrifugalize.

The young brood is distributed from the heart throughout the entire body, but the conditions necessary to its further development are found only in striated muscle; the young Nematodes penetrate the capillaries, attain the intramuscular connective tissue and then invade the fibres (Virchow, Leuckart, Graham[304]). On the ninth or tenth day after infection the first Trichinellæ have reached their destination; but further invasions are constantly taking place because the intestinal Trichinellæ live from five to seven weeks, and continue to produce their young.

[304] Trichinellæ that are unable to penetrate into muscular fibres invariably die, no matter where else they settle; their occurrence in the adipose tissue is disputed, but is still possibly correct, as bundles of muscles are present in the fat of bacon. The Trichinellæ do not settle in heart muscle, although they may reach it in cases of heavy infection; they then die or wander into the pericardium, and eventually into the heart cavities.

Symptoms.--(1) Period of invasion: Gastro-intestinal symptoms--nausea, vomiting, watery diarrhœa, colic. Muscular pains may occur even at this period. Recurrent abdominal pains about the eighth day, a temporary œdema. Embryos are abundant in the serous cavities.

(2) Period of dissemination: Second week. Myositis, variable in amount, is the predominant symptom. The biceps and calf may be hard and tender. Mastication, speech, respiration, etc., may be difficult and painful. Dyspnœa may be intense. Temperature 104° to 105° F.

(3) Period of encystment: Symptoms of marked cachexia. Third week: Second period of œdema, especially of face. Delirium, somnolence, lung affections. Death or gradual subsidence of symptoms in mild cases.

Eosinophilia (50 per cent. or more) is present.

In consequence of the new batches of young produced during several weeks, the above-mentioned symptoms of disease are often considerably aggravated; the fever increases, delirium may arise, and infiltration of the lungs, fatty degeneration of the liver and inflammation of the kidneys may ensue; the initial slight œdema may extend, the strength dwindles, and in many cases the patients succumb to the trichinosis. In severe cases improvement of the condition is only apt to occur in the fourth or fifth week; the convalescence is always protracted.

The muscular fibres attacked degenerate, the transverse striation at first disappearing; the fibres then assume a granular appearance, the nuclei multiply and become enlarged, and are surrounded by an area of granular material, which stains more deeply than the remaining contents of the sarcolemma. Two or three weeks after infection, the spirally rolled-up Trichinellæ have grown to 0·8 to 1·0 mm., and in their vicinity the muscular fibre is swollen, spindle-shaped, and the sarcolemma is glassy and thickened. The inflammation also extends to contiguous fibres, especially to the intramuscular tissue, which proliferates greatly, especially in the vicinity of the degenerated fibres. While the latter become more and more absorbed, the capsule is formed by the inflamed connective tissue, which, penetrating into the glassy and thickened sarcolemma from the poles of the spindle, forms the cystic membrane. According to other authorities, the larvæ settle in the _inter_muscular connective tissue which forms the cyst and not in the muscular fibres within the sarcolemma. The cysts are lemon-shaped and usually lie with their longitudinal axis in the direction of the muscular fibres; on an average they measure 400 µ in length by 250 µ in breadth.

Later on fat cells appear at their poles, and after about six or nine months they commence to calcify, the process starting at the poles (fig. 305). Finally, sometimes after the lapse of years, the captive Trichinellæ themselves become calcified.

According to experience, Trichinellæ are not evenly distributed in the muscular system of pigs; the diaphragm, the muscles of the larynx, tongue, abdomen and intercostal spaces are their favourite positions; this predilection for the respiratory muscles is explained by their regular contractions, owing to which regular narrowings of the capillaries take place, thus favouring the settling of the circulating Trichinellæ. The same circumstance probably explains the frequency of the parasites in the tongue.

Possibly also the Trichinellæ that bore direct through the intestine may, from the abdominal cavity, penetrate the muscles in the vicinity. Frequently also encysted Trichinellæ are found in remarkable numbers in the vicinity of the points of insertion of the tendons, this proclivity being probably connected with the fact that the Trichinellæ first of all wander into the muscular fibres and find a natural barrier at the points of insertion of the tendons.

The Trichinellæ, in their encysted condition, may remain alive and capable of development for many years--in the pig eleven years and in man as much as twenty-five to thirty-one years. Encystment, however, is not a necessary condition for the development of the brood, that is to say, Trichinellæ which reach the gut of suitable animals become sexually mature and multiply provided that they have developed so far as to possess a rudimentary genital spot, which occurs when the body is 0·5 to 0·75 mm. long, but all the same a great part of non-encapsuled Trichinæ perish on their passage through the stomach.

The black rat (Mus rattus), and more particularly the sewer rat (Mus decumanus[305]), are the normal hosts of Trichinella spiralis. These animals, especially the last-named species, infect themselves very easily, as they are cannibalistic, and they also transmit trichinosis to other species by which they are devoured, such as pigs, dogs, cats, foxes, bears and martens. Rats are infected also by the ingestion of fæcal matter from infected animals which contains trichinæ (Höyberg). Man becomes infected with Trichinella by eating the flesh, insufficiently cooked, of infected pigs, also, but more rarely, by eating the infected flesh of wild boars, dogs, cats, bears and foxes.

[305] It is still a matter of dispute and can hardly be definitely settled whether Trichinellæ were brought to Europe by the sewer rats which invaded Europe at the end of the eighteenth century, or whether they were imported with the Chinese pig in 1820 or 1830, when it was introduced into England and Germany to cross with the native breeds, or whether finally Trichinellæ are also indigenous to Europe.

The infection of pigs may likewise take place by their having access to the offal of trichinous pigs, or being actually fed on it. These are, however, exceptions, which, as a matter of course, are of great importance in certain places. As a matter of fact, the rats examined for Trichinella were always found to be severely infected. Thus Billings, in the knackers’ yard at Boston, found that 76 per cent. of the rats were infected, and in an export slaughterhouse 100 per cent. were found to harbour the parasite; in the city of Boston 10 per cent. of the rats had trichinosis. Heller found that of 704 rats, from twenty-nine different places in Saxony, Bavaria, Würtemberg and Austria, 8·3 per cent. were infected with Trichinellæ; of the rats caught in the knackers’ yards, 22·1 were diseased; of those taken in slaughterhouses, 2·3 were infected, and of rats from other localities only 0·3 per cent. harboured the parasite. Leisering found almost the same figures, but in rats from slaughterhouses 5·3 per cent. were infected.

The geographical distribution of T. spiralis does not correspond with the occurrence of trichinosis in man; local customs are an important factor; for instance, the custom of eating pork in a condition that does not affect the life of the enclosed trichinella. In places where such customs do not prevail, epidemics do not occur--at the most there are isolated cases of the disease, although there be a great number of infected pigs. The following conditions prevail in North America: In Boston, Billings found that 4 to 5·7 per cent. of the pigs examined were trichinous; Belfield and Atwood found that 8 per cent. were infected in Chicago; Salmon found on an average that 2·7 per cent. were infected (but at various places the percentage fluctuated between 0·28 to 16·3 per cent.), yet epidemics of trichinosis hardly ever occur in North America, and only isolated cases of the disease are met with in German immigrants, who keep to their native customs.

This report, according to the researches of H. U. Williams, must be considerably modified. This author has examined the muscular system of human cadavers according to the method employed by inspectors of meat for pigs. The investigations were conducted in the Pathological Institute of the University of Buffalo, and the observer has examined 505 bodies since 1894, of which 27 (= 5·34 per cent.) were invaded by Trichinella. The cases, according to the nationality, are divided as follows:--

---------------------+----------+--------+---------+------------- | | Trichinella | Percentage | Examined +--------+---------+ of positive | | Absent | Present | results ---------------------+----------+--------+---------+------------- Americans: | | | | (a) Whites | 207 | 201 | 6 | 2·89 (b) Negroes | 70 | 65 | 5 | 7·14 British and Irish | 62 | 57 | 5 | 8·06 Canadians | 12 | 10 | 2 | 16·66 Germans | 49 | 43 | 6 | 12·24 Italians | 12 | 10 | 2 | 16·66 Other nationalities | 27 | 27 | 0 | 0 Nationality unknown | 66 | 65 | 1 | 1·51 ---------------------+----------+--------+---------+------------- Total | 505 | 478 | 27 | 5·34 ---------------------+----------+--------+---------+-------------

It is worthy of remark that half of all the positive cases were mental patients, who were found to be affected with Trichinella to well-nigh 12 per cent. Trichinosis was not, however, the cause of death in any case. Very frequently the Trichinellæ were found calcified and dead.

Conditions are similar in most countries of Europe, where, of course, the number of infected pigs is considerably smaller, but the disease depends less on this than on the way in which the pork is prepared.

Cases of trichinosis have been known to occur in nearly all the countries of Europe; further, in Egypt, Algeria, East Africa, Syria, India, Australia, and America. North Germany, more especially the Saxe-Thüringian states, is the classical land for epidemics of trichinosis; the mortality varies, but it may be very high.[306]

[306] For instance, extensive epidemics occurred in Hettstädt in 1863 (160 patients, 28 deaths); Hanover, 1864–1865 (more than 300 patients); Hadersleben, 1865 (337 patients, 101 deaths); Potsdam, 1866 (164 patients); Greifswald, 1866 (140 cases, 1 death); Magdeburg, 1866 (240 cases, 16 deaths); Halberstadt, 1867 (100 cases, 20 deaths); Stassfurt, 1869 (over 100 cases); Wernigerode, 1873 (100 cases, 1 death); Chemnitz (194 cases, 3 deaths); Linden, 1874 (400 cases, 140 deaths); Niederzwohren, near Cassel, 1877 (half the population); Diedenhofen, 1877 (99 cases, 10 deaths); Leipzig, 1877 (134 cases, 2 deaths); Ernsleben, 1883 (403 cases, 66 deaths); Strenz-Neuendorf, 1884 (86 cases, 12 deaths), etc. According to Johne, 109 epidemics, with 3,402 cases and 79 deaths, occurred in Saxony between 1860 and 1889. Stiles, in a work recently published, states that there were 8,491 cases of trichinosis with 513 deaths (6·04 per cent.) in Germany from 1860 to 1880; and 6,329 cases and 318 deaths (5·02 per cent.) between 1881–1898. Of these latter, 1881–1898, 3,822 (225 deaths) occurred in Prussia, 1,634 (76 deaths) in Saxony, and 873 (17 deaths) in the remaining states. There is, however, no doubt that many deaths from trichinosis were not recognized, as proved by experience at post-mortems.

Prophylaxis.--The grave nature of the disease and the comparatively high mortality relating to trichinosis led the authorities to adopt certain preventive measures, which are the more necessary as national customs cannot be altered in a short time. As the usual process of pickling and smoking, even when long continued, does not certainly ensure the death of the Trichinellæ contained in the meat, and also because in roasting and boiling large pieces of pork a considerable time is necessary to permit the temperature required to kill off the parasites (62° to 70° C.) to penetrate to the middle of the joint, it appeared to be most practical to have all pigs microscopically examined for Trichinellæ before they, or parts of them, were placed on the market, and all infected meat condemned, no matter whether the Trichinellæ were present in large or small numbers, still undeveloped or calcified. Since 1877 obligatory examination of pork has been introduced in Prussia, though as yet it is not thoroughly carried out; other states of North Germany as well as the larger towns of South Germany soon followed; a complete army of trichina inspectors, officially examined and periodically controlled by experts, and whose number in Prussia amounted to 27,602 in 1896, this being even increased to 28,224 in 1899, have the charge of examining pork on certain lines laid down. These are at the present time uniformly administered. The proceeding is usually that the trichina inspector himself goes to the slaughterhouses, or special samplers take pieces of the muscles that are known to be the favourite seats of the parasite (pillars of the diaphragm, the costal part of the diaphragm, muscles of the tongue and larynx, intercostal and abdominal muscles); six small portions are separated from each piece, pressed between slides or special compressors, and carefully gone through by examining them with a low power of the microscope. The pigs free from Trichinellæ are passed for commerce; trichinous pigs, on the other hand, in Prussia, are only allowed to be used for industrial purposes, i.e., the hide and bristles are used, the fat is allowed to be melted down, or certain parts are used for the manufacture of soap or glue. In Saxony, however, it is still permitted to place trichinous flesh on the market, fully declaring its nature, and after having been heated to its deepest strata at a temperature of 100° C. in a suitable apparatus, and under the supervision of a veterinary surgeon.

AS TO THE PROPORTION OF TRICHINOUS PIGS to healthy ones, the following tables give the figures for Prussia:--

------+---------------+-----------------+------------ | Number of | Number of | Year | pigs examined | trichinous pigs | Proportion ------+---------------+-----------------+------------ 1878 | 2,524,105 | 1,222 | 1 : 2,065 1879 | 3,164,656 | 1,938 | 1 : 1,632 1881 | 3,118,780 | 1,695 | 1 : 1,839 1882 | 3,808,142 | 1,852 | 1 : 2,056 1883 | 4,248,767 | 2,199 | 1 : 1,932 1884 | 4,611,689 | 2,624 | 1 : 1,741 1885 | 4,421,208 | 2,387 | 1 : 1,852 1886 | 4,834,898 | 2,114 | 1 : 2,287 1887 | 5,486,416 | 2,776 | 1 : 1,988 1888 | 6,051,249 | 3,111 | 1 : 1,945 1889 | 5,500,678 | 3,026 | 1 : 1,818 1890 | 5,590,510 | 1,756 | 1 : 3,183 1891 | 6,550,182 | 2,187 | 1 : 2,996 1892 | 6,234,559 | 2,085 | 1 : 2,992 1896 | 8,759,490 | 1,877 | 1 : 4,666 1899 | 9,230,353 | 1,021 | 1 : 9,040 1902 | 9,093,210 | 725 | 1 : 12,397 ------+---------------+-----------------+------------

The proportion, however, is not only subject to variation in separate years, but differs according to the district; thus, in 1884, in the state district of Minden there was one trichinous pig to 30,146 healthy animals, in Erfurt 1 to 14,563, in the district of Gnesen 1 to 101, in Schrimm 1 to 86, and in Schroda 1 to 68.

In Germany Trichinella is becoming LESS COMMON in pigs (Ostertag):--

(a) Prussia.

Pigs found Year to be trichinous 1878–1885 0·061–0·048 per cent. 1886–1892 0·033–0·043 " 1896 0·021 " 1899 0·014 " 1902 0·011 "

(b) Saxony.

Number of pigs Year found to be trichinous 1891 0·014 per cent. 1892 0·011 " 1893 0·008 " 1894 0·007 " 1895 0·012 " 1896 0·0102 " 1899 0·004 " 1902 0·0056 "

(c) City of Berlin.

Number of pigs Year found to be trichinous 1883–1893 0·035–0·064 per cent. 1893–1897 0·022–0·015 " 1902 0·006 "

There is no doubt that the excellent preventive measure of official inspection for Trichinella has led to the avoidance of grave disasters; its introduction has not yet caused an entire cessation of trichinosis in man, because inspection of pork is not obligatory everywhere, so that human beings may become infected by unexamined trichinous pigs from their own country or from abroad, and also because an infection may occasionally escape notice. For these reasons the meat imported into Berlin from abroad as free from Trichinæ is examined again and not always in vain; finally, also, gross negligence may at times occur, or fatal errors may be made.

In addition private prophylaxis must not be neglected, and its chief aim should be directed to the suitable preparation of pork.

Family. *Dioctophymidæ.*

Genus. *Dioctophyme*, Collet-Megret, 1802.

Syn.: Eustrongylus, Dies., 1851.

Large worms. Anterior extremity unarmed; the mouth is surrounded by six papillæ. One ovary. The vulva is in the anterior region of the body.

*Dioctophyme gigas*, Rudolphi, 1802.

Syn.: Dioctophyme renale, Goeze, 1782; Ascaris canis et martis, Schrank, 1788; Ascaris visceralis et renalis, Gmelin, 1789; Strongylus gigas, Rud., 1802; Eustrongylus gigas, Dies., 1851; Strongylus renalis, Moq. Tand., 1860; Eustrongylus visceralis, Raill., 1885.

Colour blood-red; the anterior extremity somewhat slender; there is a series of about 150 papillæ along the lateral lines; the sub-median lines are strongly developed, and from them spring the radial muscles for the intestine.

The males attain a length of 40 cm. and a diameter of 4 to 6 mm.; the posterior extremity is transversely truncated; the anal orifice is within the base of the collar-like bursa, the thickened edges of which are beset with papillæ; the spicule measures 5 to 6 mm. in length.

The females attain a length of 100 cm. and a breadth of 12 mm. The anus is crescent-shaped and terminal. The vulva is 50 to 70 mm. distant from the anterior extremity. The eggs are oval and have a thick shell presenting numerous depressions; the shell itself is brownish, but it is colourless at the somewhat thickened poles; it measures 60 µ in length by 40 µ in breadth. The larva measures 240 µ by 14 µ.

Dioctophyme gigas lives in the pelvis of the kidney, more rarely in the abdominal cavity of the seal, otter, dog, wolf, fox, horse, marten and polecat, exceptionally also in human beings. It also occurs in tumours of the mamma and perinæum. Most of the cases in which this parasite has been reported as occurring in man may be traced back to unrecognized Ascaris lumbricoides or to clots of fibrin; seven certain cases, eight more or less doubtful, however, remain.

The source of infection is unknown, but according to Balbiani the eggs develop an embryo in water or moist soil, and this embryo may remain alive several years without hatching; the infection of dogs with embryo-containing eggs did not succeed; an intermediate stage in fishes is conjectured, but still the infection of cattle and horses is unintelligible.

Family. *Strongylidæ.*

Sub-family. *Metastrongylinæ*, Leiper, 1908.

Buccal capsule absent or slightly developed, vagina elongate, uteri convergent[307] and have a simple musculature. Parasitic in the respiratory or circulatory system. Genera: Metastrongylus, Synthetocaulus.

[307] Convergent: i.e., the uteri are parallel, converging from the anterior part of body to the vagina, which is near the anus, this position being associated with convergence of the uteri. Divergent: Uteri run anterior and posterior, diverging from the vagina, which in this case is near middle of body.

Genus. *Metastrongylus*, Molin, 1861.

Mouth with six lips, of which the two lateral are the largest. Postero- and postero-external rays[308] of bursa thin, the rest thick. Only the median ray double. Spicules very long and slender, striated. Vulva immediately in front of anus. Eggs contain an embryo when laid.

[308] For nomenclature of rays vide p. 449.

*Metastrongylus apri*, Gmelin, 1789.

Syn.: Gordius pulmonalis apri, Ebel, 1777; Ascaris apri, Gmelin, 1789; Strongylus suis, Rud., 1809; Strongylus paradoxus, Mehlis, 1831; Strongylus elongatus, Duj., 1845; Strongylus longevaginatus, Dies., 1851.

The male measures 12 to 25 mm. in length; the bursa is bilobed; there are five rays in each lobe; the spicules are thin and up to 4 mm. in length. The females measure 20 to 50 mm. in length, the anus is close in front of the posterior extremity, which has a recurved, hook-like process; the vulva is close in front of the anus. The eggs are elliptical, 57 µ to 100 µ in length, 39 µ to 72 µ in breadth; when the eggs are deposited the embryo is already formed, 220 µ to 350 µ by 10 µ to 12 µ.

Metastrongylus apri frequently lives in the bronchial tubes--usually the smaller ones--of the pig[309] and wild boar; it is also found occasionally in sheep and in man; in young pigs it is apt to set up a bronchitis, which frequently causes death.

[309] The reports of the city inspection of meat in Berlin state that Strongylidæ in the lungs of pigs are by no means rare; therefore the lungs of 1,941 pigs were condemned between 1885–1886, of 1,641 between 1886–1887, of 3,237 between 1887–1888, of 4,855 between 1888–1889, of 7,197 between 1889–1890, and of 5,574 pigs between 1890–1891, etc. Ostertag found Strongylus apri in 60 per cent. of the pigs examined in the Berlin abattoir; Meyer, in Leipzig, found the parasite in 15 per cent. of the native pigs and in 52 per cent. of the Hungarian pigs.

The first communication as to the occurrence of this species in man was that of Diesing, who, in 1845, in Klausenburg, had the opportunity of examining Strongylidæ found by Jortsits in the lung of a little boy, aged 6, in Transylvania; probably also the Nematodes found in the trachea and larynx of man, and described by Rainey and Bristowe as specimens of Filaria trachealis, belong to this group; according to Chatin, Metastrongylus apri may also occur in the intestine of man; this occurrence, however, may in all probability have been due to an accidental introduction of adult worms into the intestine, and should not be attributed to an infection by the larval stage.

No experiments to induce infection have been made; it is probable, however, that infection is direct and without the aid of an intermediate host.

Sub-family. *Trichostrongylinæ*, Leiper, 1908.

Strongylidæ with buccal capsule absent or slightly developed, vagina short, uteri divergent (i.e., anterior and posterior), ovejectors differentiated. Parasitic in the alimentary canal. Contains the genera Trichostrongylus, Hæmonchus, Ostertagia, Nematodirus, Cooperia, Dictyocaulus.[310]

[310] Dictyocaulus is parasitic in the bronchi.

Genus. *Trichostrongylus*, Looss, 1905.

Very small Strongylidæ. Mouth with three small lips and nodular or punctiform papillæ. Cervical papillæ absent. Bursa entirely closed, with large lateral lobes, and median lobe not distinctly defined. Anterior[311] rays double, the branches widely divergent, one thin, the other thick, and close to the antero-median. The postero-median ray is thin and close to the postero-external. Posterior ray bifurcate, each branch bifid at the tip (fig. 311). Spicules short, spoon or spatula-like, with on the broad anterior end a lateral knob or disc and in front of the point an angular projection. Gubernaculum of a peculiar canoe or shoe shape in profile. Vulva in the hinder half of the body. Tail with two minute papillæ just in front of tip. Eggs thin shelled; when laid they show eight to thirty-two segments. Parasitic in duodenum, seldom in the stomach of herbivora.

[311] When the anterior ray is double, the branches of it are called antero-anterior and latero-anterior.

*Trichostrongylus instabilis*,[312] Railliet, 1893.

[312] Identical with T. colubriformis of the sheep according to Leiper. If so, this latter name has priority.

Syn.: Strongylus instabilis, Railliet, 1893; Strongylus subtilis, Looss, 1895.

Male 4 to 5·5 mm. long, 0·08 mm. thick in front of bursa. Spicule 0·135 to 0·145 mm. long, accessory piece (gubernaculum) 0·07 mm. thick. Antero-external ray usually thickest of all, occasionally only as thick as the antero-median; postero-median far more slender than the antero-external and antero-median and nearer to the postero-external than to the antero-median. Female 5 to 6 mm. long, vulva 1·05 to 1·2 mm. distant from the tip of the tail, placed longitudinally, 50 µ to 55 µ long, always shorter than the unpaired portion of the canal formed by the union of the two ovejectors; anus 0·055 to 0·07 mm. distant from tip of the tail; ova 73 µ to 80 µ by 40 µ to 43 µ.

This species lives in the duodenum, exceptionally also in the stomach of Ovis aries, O. laticauda, Antilope dorcas, Camelus dromedarius (Egypt), Cynocephalus hamadryas (North Africa), sheep and goats (France), and has been found by Looss in bodies of fellaheen at Alexandria and in the stomach of a Japanese female by Ijima.

*Trichostrongylus probolurus*, Railliet, 1896.

Syn.: Strongylus probolurus, Railliet, 1896.

Male 4·5 to 5·5 mm. long, in front of bursa 0·08 mm. thick; spicule 0·126 to 0·134 mm. long, gubernaculum 0·075 to 0·08 mm. long. Bursa: latero-anterior rib thickest; antero-external thicker than antero-median, postero-median and postero-external very short and close together. Female 4·5 to 6 mm. long, vulval opening 1·08 to 1·25 mm. from tip of tail, placed longitudinally, and slightly curved, 76 µ long, always longer than the unpaired portion of the ovejector; anus 0·040 to 0·05 mm. distant from tip of tail. Posterior end thick, point of tail short. Ova 76 µ to 80 µ by 43 µ to 46 µ.

Habitat.--In the duodenum of Ovis aries, O. laticauda, Antilope dorcas, Camelus dromedarius (Egypt) and occasionally also in man (Egypt).

*Trichostrongylus vitrinus*, Looss, 1905.

Male 4 to 5·5 mm. long, in front of bursa 0·085 mm. thick. Bursa larger than in the other two species, antero-external rib thickest, antero-anterior and postero-median equally thick, straight. Spicule 0·16 to 0·17 mm. long, gubernaculum 0·085 to 0·095 mm. long. Female 5 to 6·5 mm. long, vulval opening 1·15 to 1·25 mm. distant from tip of tail, crescent shaped, oblique to body axis, and around it irregular thickenings. Ova 84 µ to 90 µ by 46 µ to 50 µ.

In duodenum of Ovis aries, O. laticauda, occasionally in Camelus dromedarius and in man (Egypt).

Genus. *Hæmonchus*, Cobb., 1898.

Small mouth cavity contains a “tooth” or “lancet” arising from the dorsal side. Cuticle of head and neck not inflated. Cervical papillæ well marked. Bursa bilateral, with large lateral lobes and a small dorsal lobe not median, but lateral, attached to the base of one of the lateral lobes (fig. 316). Posterior ray bifurcate, each branch bifid apically. Each lateral lobe six rays. Anterior rays separated distally, curving forward. Antero-median and postero-median rays distally curve away from the antero-external. Postero-external ray long and slender. Spicules less than 1 mm. Gubernaculum present. Vulva in posterior part of body covered by a prominent tongue-like flap. Eggs ellipsoidal.

*Hæmonchus contortus*, Rudolphi, 1803; Cobb., 1898.

Dorsal “tooth” or “lancet” 10 µ to 15 µ long. Cervical papillæ 0·3 mm. from head.

Male 20 mm. long by 400 µ thick (maximum). Asymmetrical lobe of bursa 150 µ by 125 µ attached to left lateral lobe. Posterior ray bifurcate; each branch bifid. Stem of ray less than twice as long as its branches. Spicules 300 µ to 500 µ with knobbed tips, and the left spicule with a barb 20 µ from the tip, right spicule with a barb 40 µ from tip. Gubernaculum 200 µ by 25 µ to 35 µ, fusiform with thickened edges.

Female 18 to 30 mm. by 500 µ (maximum). Vulva 3 to 4·5 mm. from tip. Linguiform flap 0·5 mm. (a second one exists, according to Brumpt). Anus 400 µ to 630 µ from tip. Tail acutely pointed. Eggs 75 µ to 95 µ by 40 µ to 50 µ.

Habitat.--Fourth stomach of cattle, sheep, antelope.

Distribution.--Europe, America, Africa, Asia, Australia, New Zealand. Once in man in South America by de Magalhães.

Pathology.--Produces anæmia, emaciation, dropsy in sheep; and in the human case the symptoms were mistaken for those of ancylostomiasis.

Life-history.--Rhabditic embryos easily hatch in water, then moult several times, becoming eventually “filariform” larvæ enclosed in the moulted skin. These crawl up blades of grass and are swallowed by sheep, etc.

Genus. *Nematodirus*, Ransom, 1907, emend. Railliet, 1912.

Head over 50 µ in diameter. Cuticle may be slightly inflated and often transversely striated. Cuticle with eighteen distinct longitudinal ridges. Cervical papillæ absent (?). Posterior lobe of bursa reduced to short lobules each with a dorsal ray. Antero-anterior + latero-anterior (= anterior double) rays close together, parallel; antero-external ray diverges widely from antero- and postero-median, which are close together and parallel. Postero-external ray slender. Spicules more than 0·5 mm. long, at most one-twelfth of body, united by a membrane throughout their length or only distally. Gubernaculum absent. Vulva behind middle of body. Eggs ellipsoidal, shell rather thick.

Habitat.--Duodenum of ruminants.

Sub-genus. *Mecistocirrus*, Railliet, 1912.

Head slightly inflated, with transverse striations. Skin with eighteen longitudinal ridges, but little apparent; cervical papillæ distinct. Bursa bilobed; median ray double (= postero-median + antero-median); very large antero-external at the edge, close to the anterior. Spicules very long, slender, one-sixth length of body (3·5 mm.); tail pointed. Vulva immediately in front of anus.

Habitat.--Stomach of ruminants.

*Mecistocirrus fordi*, Daniels, 1908.

Syn.: Strongylus fordi, Daniels, 1908; Strongylus gibsoni, Stephens, 1909; Nematodirus fordi, Leiper, 1911.

Male 21 mm. long by 0·4 mm. thick. Cervical papillæ 0·45 mm. behind the head. Spicules about 7 mm. long, i.e., one-third of the body length. At the level of the postero-external rays of the bursa, the bursa has a projecting lobule.

Female 25 mm. long. Anus 0·2 mm., vulva 0·5 mm. from the tip of tail. Eggs 100 µ by 53 µ.

Sub-family. *Ancylostominæ*, Railliet, 1909.

Strongylidæ with buccal capsule, well developed. Uteri divergent. Parasitic in the alimentary canal, exceptionally in the respiratory system.

Group. *Œsophagostomeæ*, Railliet and Henry, 1909.

Bursa with anterior and median ray cleft (not double), postero- and postero-external arising from a common trunk, posterior bifurcated, each limb bidigitate.

Contains at present four genera: (1) Ternidens, (2) Chabertia, (3) Œsophagostomum, (4) Agriostomum.

Genus. *Ternidens*, Railliet, 1909.

Buccal capsule sub-globular, opening obliquely in the dorsal surface, and having at the bottom three complex teeth resembling those of Triodontophorus.[313] Two crowns of leaflets; peristomic collar moderate, edge of bursa slightly toothed.

[313] Triodontophorus belongs to the group Cylicostomeæ, which has the following bursal formula: (1) anterior cleft, (2) median double, (3) postero-external and posterior arising separately, (4) posterior double, each branch giving off two lateral branches.

Type.--T. deminutus, Railliet and Henry.

*Ternidens deminutus*, Raill. and Henry, 1905.

Syn.: Triodontophorus deminutus, Raill. and Henry, 1905.

Body relatively thick. Cervical papillæ 0·5 mm. behind the head. Buccal capsule 40 µ deep. Teeth 40 µ long.

Male 9·5 mm. long by 560 µ thick. Œsophagus 660 µ long. Bursa broader than long, the lateral lobes united by a small posterior lobe with slightly sinuous margin; edge of bursa finely toothed. Spicules about 900 µ long.

Female 12 to 16 mm. long by 650 µ to 730 µ thick. Œsophagus 860 µ long. Vulva forms a distinct projection 480 µ from tip of tail. Anus 240 µ to 270 µ from tip. Eggs 60 µ to 80 µ by 40 µ.

Habitat.--Large intestine of a negro (Comoro Islands) and in the natives of Nyasaland and Portuguese East Africa. Also in large intestine of Macacus sinensis and Macacus cynomolgus.

Genus. *Œsophagostomum*, Molin, 1861.

No teeth. Cuticle around the mouth dilated to form a narrow cuticular “peristomic collar.” Separated by a constriction from this is a much more extensive inflation, the “cephalic vesicle,” bounded abruptly behind on the ventral side by a transverse groove, the “ventral cleft,” which is always present even in absence of the vesicle. Buccal cavity of slight depth with a short dorsal tunnel. Internal margin of the mouth armed with chitinous leaflets (“external crown”); internal border of the buccal capsule armed with short tongue-like leaflets (internal crown). Lateral membranous wings may extend backwards from the ventral cleft. Cervical papillæ present. Bursa with two lateral lobes united by a smaller median lobe. Spicules over 5 mm. long, slender; gubernaculum inconspicuous. Vulva in front of anus. Adults usually in large intestine of ruminants, suidæ, tapirs, edentates and apes. Larvæ sometimes in nodules in intestinal wall.

*Œsophagostomum brumpti*, Railliet and Henry, 1905.

Female immature, 8·5 to 10·2 mm. long, 0·295 to 0·325 mm. thick. Cuticle transversely striated. The cephalic vesicle immediately behind the vestibulum oris, embracing the anterior two-fifths of the œsophagus, extending ventrally, however, towards its posterior end. Vestibulum oris formed by a cuticular band provided with a crown of twelve apical leaflets directed forward and inwards; six cephalic papillæ (two lateral, four submedian); buccal capsule in front of cervical swelling not delineated circularly behind, but provided with three wide incisions (one dorsal, two sub-ventral). Œsophagus, 0·470 to 0·500 mm. long, two cervical papillæ at five-eighths of its length. Vulva 0·350 to 0·475 mm., anus 0·170 to 0·200 mm., before tip of tail.

Habitat.--Found by Brumpt in tumours of the cæcum and colon of a native of the River Omo (Lake Rudolph), East Africa. Immature forms only were present. Adults have been found in similar tumours in monkeys.

Pathology.--They occur in hæmorrhagic cysts in the submucosa or muscularis mucosæ of the gut wall. The cysts project internally and externally, and contain immature adults, which eventually escape into the lumen of the gut.

*Œsophagostomum stephanostomum* var. *thomasi*, Raill. and Henry, 1909.

Body thick, pointed only at the ends. Buccal capsule much reduced. External crown of thirty-eight leaflets (the “crown” nearest the centre of fig. 319, 5). Male 17 to 22 mm. long by 750 µ thick. Spicule 1·380 to 1·475 mm., slightly curved at the tip. Female, immature, 16 to 20 mm. long by 900 µ thick, tail ending in a little conical appendage. Anus 230 µ, vulva 500 µ to 525 µ from tip. Ovejectors close together. Uteri very short in form of oblong pouch.

Œs. stephanostomum, Stossich, 1904, in the large intestine of gorilla. Œs. stephanostomum var. dentigera, Raill. and Henry, 1909, in the chimpanzee.

Habitat.--In large and small intestine of man, Brazil.

Pathology.--Nodules occur in the gut wall; 187 were found by Thomas in his, the sole case. The tumours contain each a single worm.

*Œsophagostomum apiostomum*, Willach, 1891.

According to Leiper, Œs. brumpti is identical with, and hence a synonym of, this species. Parasitic in large intestines of monkeys, producing dysentery, and in man (Northern Nigeria).

According to Walker this species is common in Philippine monkeys. Ova are scanty in the fæces. They measure 73 µ to 84 µ by 44 µ to 57 µ and are in the morula stage. They are easily cultivated. The rhabditiform larva is 340 µ by 16 µ and has a long filiform tail. It moults twice, and at the second moult becomes a filariform larva retaining the skin of this moult, this stage being that of the mature larva. It now measures 9 mm. long by 30 µ thick. Walker suggests that the mode of infection is similar to that of ancylostomes.

Group. *Ancylostomeæ*, Railliet and Henry, 1909.

Bursa with anterior ray cleft, median double,[314] postero- and postero-external arising from a common trunk, posterior bifurcate, each limb being tridigitate. Vulva in posterior third of body. Uteri divergent.

[314] I.e., with a distinct space between the limbs.

Contains the following genera: (1) Strongylus,[315] (2) Ancylostoma, (3) Uncinaria, (4) Characostomum, etc.

[315] Strongylus (Syn.: Sclerostomum) differs slightly in its posterior ray from the other genera of the group. Each bifurcation is trifurcate rather than tridigitate.

Genus. *Ancylostoma*, Dubini, 1843, emend. Looss, 1905.

Ventral margin of mouth capsule armed with teeth, the “roots” of which are continued backwards and appear on the external surface of capsule as rib-like thickenings. Terminal third of dorsal ray cleft. Genital tubes very long, with short, closely packed diagonal convolutions.

*Ancylostoma duodenale*, Dubini, 1843.

Male 9 mm. long by 0·45 mm. thick, female 12 mm. long by 0·6 mm. thick. Pale flesh colour, or an intense red in posterior third. Anteriorly may be more or less black due to (blood) pigment in the cells of the chyle intestine (= stomach + small intestine). The worm is about the same thickness all through and is plump and rigid. Cuticle striated. The body has a marked torsion, so that if the ventral side of the head is upwards the anus appears to open laterally and vice versâ. The dorsal curve of the head end is only slight and the œsophagus is roughly cylindrical.

Buccal Capsule.--The buccal capsule is bent dorsally, 0·21 mm. long, 0·19 mm. broad. If a worm is rolled under the cover-glass so that the dorsal side is upwards, we observe the following features (fig. 325): In the dorsal edge of the chitinous capsule there is a gap as if a *U*-piece had been punched out. This is the “dorsal gap or incision.” The so-called “dorsal teeth” are simply the rounded edges of the tips of this gap. They project beyond the skin which covers the capsule externally. Below this gap is seen a curved line which, if followed along the sides of the capsule on each side, merges into the base of the most posterior ventral tooth. This line is the optical expression of a very shallow groove on the inside of the capsule. The skin on the outside of the capsule, which is reflected over the edge of and into the capsule, dips into this groove, which gives it a firm attachment. Below the middle (dorsally) of this curved line there is a thickening in the capsule wall, which is perforated by the opening of the dorsal œsophageal gland. This is the “dorsal ridge”; in optical section it has a conical appearance with a lumen (of the duct).

On the ventral wall one sees the two pairs of strong teeth, their points being directed somewhat backwards. They are covered by cuticle above and below, but their points are free, piercing the cuticle. The “roots” of these teeth followed backwards appear as two thickenings or ribs on the outside of the capsule wall, so that the outside wall is not smooth--a characteristic of the genus Ancylostoma. In the space between these ribs lies the ventral nerve papilla, and lying against the outside of the outer root the lateral nerve papilla. The nerve papillæ are thus, as it were, concealed by these roots, and not conspicuous as they are in Necator. Following the ventral curve of the capsule on the inside, posteriorly we next find two triangular ventral lancets.[316] These stand straight up into the capsule on either side of the longitudinal axis, converging at their summits. So that to sum up, the cutting apparatus is entirely ventral, consisting of two pairs of cutting teeth and a pair of lancets.

[316] The ventral lancet (of one side) of Necator is seen in fig. 335.

Cervical Papillæ.--Two, one on each side behind the head at the level of the excretory pore. They consist of “pulp,” i.e., extensions of the substance of the lateral bands covered by cuticle and supplied with a nerve (fig. 326).

Œsophageal Glands (3).--The chitin of the triradiate œsophagus is continuous with that of the buccal capsule. In its muscular walls are three glands--one dorsal, two sub-ventral. The dorsal gland opens into the buccal cavity through the dorsal ridge; the two others into the lumen of the œsophagus at the nerve ring. They branch freely amidst the muscles. They are probably digestive in function.

Cephalic Glands (2).--Lie in the lateral lines or bands on either side. They begin about the middle line of the body, and their ducts open at the base of the outer ventral tooth on the surface of the skin on each side. Each is 0·15 mm. thick in the middle, and has a single nucleus about as big as an ancylostome egg (N, fig. 323). They probably function as poison glands.

Excretory System and Cervical Glands (2).--The excretory pore lies in the mid line ventrally behind the œsophageal nerve ring (figs. 324 and 326). It opens into the excretory vesicle, a cavity in a large cell with lateral appendages which fuse with the lateral lines, this cell thus forming the “bridge” of the excretory system. Adhering to this (bridge) cell are the spindle-shaped cervical glands (Glc, fig. 324), and branches from the excretory vesicle enter the glands, which are excretory in function; the vesicle also receives branches from the lateral excretory canals (fig. 326) running in the lateral lines or bands. The cervical glands are swollen anteriorly, forming the so-called ampullæ just in front of the bridge. They extend backwards a little beyond the anterior loop of the testis.

Lateral Lines.--(1) Are broad elevations of the subcuticle, in which, here and there, a nucleus occurs. (2) Near the bursa in the male they increase in volume, and finally divide into branches which form the “pulp” of the different rays. (3) In addition to the lateral lines or bands, there is also a dorsal and ventral band. (4) The ventral band is well developed caudally, forming a large pad dorsal to the cloaca, “pulvillus post-analis.”

The bursal rays are outgrowths of the lateral lines. Beside this “pulp” they contain a nerve, and at their bases complex muscles.

The Bursa is closed on all sides with a short median (ventral) lobe, which may be tucked inwards. It is an outgrowth of the inner layer of the skin pushing the outer layer before it, so that it consists of three layers, not four, as it would be if it were a fold. The bursa is twice as broad as long. It is supported by a variety of rays, the arrangement of which is best followed from the figure (fig. 327). The different terminology for these rays as used by various authors should be noted: Ventral = anterior; externo-lateral = antero-external; medio-lateral + postero-lateral or antero-median + postero-median = median (doubled); externo-dorsal = postero-external; dorsal = posterior. All the rays end in tactile papillæ, seven, on each side; the postero-external and antero-external on the outer surface of the bursa, the five others on the inner surface.[317] Of the six terminal digitations of the dorsal ray, only the external two contain tactile papillæ.

[317] This also occurs in other Strongylidæ, e.g., in the genus Strongylus (Syn.: Sclerostomum).

In the male there are prebursal papillæ and minute caudal papillæ in the female.

In the female the inner layer of the cuticle projects at the posterior end as a sharp spike, 20 µ long, which may sometimes be broken off.

Ovaries.--The anterior tube runs from the cephalic to the posterior end and back again. The posterior tube begins anteriorly, runs to the posterior end of the body, and then back to the cephalic end, forming a vulval loop before ending. The ovaries on the whole run in oblique coils. The uterus is the thicker portion of the tube, 5 mm. long. A short tube connecting the ovary and uterus is the oviduct. The two uteri unite to form a single duct, the vagina, opening 1 mm. behind the middle line. The portion of the uterus next to the oviduct functions as a seminal receptacle, whereas the part next the vagina functions as an ovejector.

Testis.--The blind end begins a little behind the beginning of the cement gland. The transverse coils occupy the middle third of the body. About the middle of the body it passes into the spindle-shaped seminal vesicle, which, with the spicular canal and rectum, opens into the cloaca. An anterior longitudinal coil pushing in between the cervical glands is characteristic of Ancylostoma. The cement gland surrounds the ejaculatory duct for practically its whole course, and it occupies nearly the posterior half of the body and secretes a brown or black cement. The spermatozoa are curved rods about 2 µ long.

Spicules are 2 mm. long, ending in a fine point. They are moved by exsertor and retractor muscles. At first they lie free in the body cavity; next in a groove in the dorsal wall of the cloaca; then in an isolated canal, and finally in two canals. Anteriorly each has two longitudinal crests on its inner surface. These meet the corresponding crests of the other spicule, and so form a canal along which the sperm passes into the female. The gubernaculum is a thickening of the dorsal wall of the cloaca. It is not a free piece, but is moved by various muscles.

Genital Cone is a prominence on the floor of the bursa on the ventral side of the body, on which the genito-anal orifice opens. The cone is only slightly marked in Ancylostoma duodenale, but is much more prominent in Necator americanus.

Distribution.--Africa, Egypt, Europe, Japan, China (mainly), but in association with Necator americanus in Southern States of America, British India, Assam, Burma, Hongkong, Liberia, Jamaica, Martinique, Costa Rica, Colombia, Antigua, Guadeloupe.

Habitat.--The worms live in the jejunum, less frequently in the duodenum, of man only.

Food.--The worms feed on the mucous membrane of the gut, attaching themselves to the base of the villi, sucking these in; and when these are destroyed they attack further the submucosa. As a rule the worms have no blood in the gut, but in their attack on the submucosa a blood-vessel may be eroded, and so the gut of the worm filled with blood.

Development.--The eggs are oval with broadly rounded poles, 56 µ to 61 µ by 34 µ to 38 µ. In fresh fæces they contain four granular nucleated segmentation masses of the ovum (fig. 329) separated by a clear space from the shell.

Egg of Ancylostome appears to have a single contour. Under high powers this appears double, but they are the outer and inner surface of the true (chitinous) egg-shell. Internal to this is the extremely delicate yolk-envelope, a kind of skin secreted by the egg cell around itself for protection. The function of this is probably to absorb water to swell and burst the outer chitinous shell. The embryos when hatched are termed larvæ.

Embryos which are ready to hatch have their bodies almost free from granules; others, though apparently mature, that have granules will not hatch.[318]

[318] TABLE OF DIFFERENCES BETWEEN LARVÆ OF A. duodenale AND S. stercoralis.

--------------+----------------------+------------------------------ | A. duodenale | S. stercoralis --------------+----------------------+------------------------------ (1) Vestibulum| | } oris |1·8 µ broad |3 µ }Rhabditiform. (2) Genital | | } rudiment|3 µ to 5 µ long |25 µ to 33 µ } | | (3) Thickness |Thicker | -- } (4) Œsophagus |One-fourth body length|Half body length} (5) Tail |Pointed |Two fine points }Filariform. (6) Motion |Less active than | -- } (7) Gut |Soon fills with dark | } | granules | -- } --------------+----------------------+------------------------------

Larva.--Stage I: Average length, 25 mm. Maximum thickness in œsophageal region, 17 µ. Head end fairly blunt, from behind the anus (the tail) tapering in an uniform manner. Buccal cavity is characteristic, 10 µ to 12 µ by 1 µ to 8 µ, longer and narrower than the corresponding larvæ of Strongyloides stercoralis. Œsophagus “rhabditic” in character, i.e., it has three sections, but they are not so clearly marked off as in larvæ of the genus Rhabditis. The posterior bulb has a *Y*-shaped valve, the function of which, according to Looss, is to prevent regurgitation of food. The granules of the gut serve as a reserve of food, and are used up if the larvæ are starved. The genital rudiment consists of two cells half-way between the end of the œsophagus and the anus in the mid-ventral line. The larva lives on fæcal matter and grows to about 0·4 mm., then moult[319] I takes place in two days or more, the skin being ruptured by the activity of the larva.

[319] Moults take place by the formation of a new skin below the old one, the two being in close apposition at first.

Stage II: The larva is now in this stage, which does not differ much from the previous one. It grows to 0·5 mm. The mouth opening closes. The œsophagus elongates, becoming cylindrical or “filariform”; a new skin is formed underneath the old one, and in about a week moult II takes place.

Stage III: The mature larva remains enclosed in the old skin. Its movements are now much more active and of a boring character. Length is now 0·6 mm. This mature stage has been erroneously called the encysted larva, because there is no cyst secreted from its surface by the larva, but it is simply the old skin, which is not cast off, but is retained for purposes of protection, as the larva is free living, but casts it as soon as it assumes parasitic life again. From the egg to this mature stage is thus six to ten days.

Bionomics of Development.--Air: Eggs can develop when shut off from the air for a “comparatively long” time.

Temperature: Hatching takes from eight hours upwards. Eggs develop best at 25° to 30° C., but will not develop below 8° to 10° C. The larvæ, however, will stand freezing.

Moisture: Eggs and larvæ do not live long under water, because they suffocate or starve, but mature larvæ will live for months (six to twelve) in water; they require no food--in fact, can take none in--but live on their reserve granules, and in course of time become as clear as glass.

Thigmotropism: The mature larvæ, after casting their skin, will penetrate pith, climb up stems, stalks, etc., and creep into any pore.

It is important to recognize that this third stage of the mature larva is the only infective one.

Mode of Entry into the Body.--Infection is effected through the mouth (Leichtenstern and others), and also through the skin, as was first discovered by Looss and afterwards confirmed from the most diverse quarters, partly in the case of Ancylostoma duodenale, partly in that of A. caninum in dog, man, and monkey. The larvæ that gain access to the intestine partly through contaminated food, or through unwashed hands, or under some circumstances through water, first throw off their “sheath”--that is, they complete moult II. Moult III takes place four to five days after they have reached the gut, and they now have a mouth capsule supplied with four small teeth arranged crosswise, enabling them to fasten on to the intestinal epithelium, upon which they feed. On this food the worms grow in four to six days to 3 to 5 mm. in length, and now moult IV. takes place, thus attaining their definite shape and distinctive character. About eight days later the sexual organs commence to function; at this time the first copulation should be taking place--it will later be frequently repeated--and a few days later the first ova are laid, first in less and later in larger numbers, so that they appear in the fæces about four to five weeks after the infection.[320]

[320] From the number of eggs present in a given quantity of fæces, the number of female Ancylostomes present in the gut can be reckoned by a formula of Leichtenstern’s (x = a/47, in which a signifies the number of eggs counted in a single gramme of fæces).

Infection by the Skin.--Mature larvæ, which are placed on the skin of man or suitable animals, cast their “sheath” and bore their way through delicate fissures either horizontal in the superficial scales of the epidermis, or through vertical fissures into hair follicles where these exist, and then they invade the cutis. Now according as they migrate further into the lymphatic vessels or the small vesicles, the final path to the gut differs to some extent. The blood path leads to the right heart, and from there into the lungs; here the larvæ leave the blood stream and enter the air passages, over the mucosa of which they travel further headwards, through the bronchi into the trachea and larynx, and from hence through the œsophagus to the stomach; in some cases also they are swallowed. The lymphatic path leads finally also into the blood stream, but the lymphatic glands must first be passed, and in these many larvæ are retained and perish. In the cutaneous infection seven to ten weeks elapse till the time of appearance of the first ova in the fæces.

The penetration of the skin by the larvæ also in man causes reddening and burning at the affected points, and this is followed in a few days by transitory swelling in the subcutaneous connective tissue. Skin affections can also be set up by such Ancylostoma (and Strongyloides) larvæ as do not gain access to the blood or lymphatic vessels or gut; such larvæ apparently wander further in the connective tissue, and, as Looss has in his own person observed, gain access to the cutis at different points, thus causing progressive swellings (accompanied by intense itching), which cease when the worm again penetrates into the deep tissues. Skin affections such as “ground-itch” or “pani-ghao” occurring in the tropics and only attacking the feet, or other affections (e.g., sump bunches) are now well recognized as being due to the invasion of Ancylostoma larvæ.

Other names for these skin affections are water-sore, sore feet of coolies, maza-morra, bunches, botches, quaddeln, krätze, ampoules, gourmes, taons, pitirr. Whether oral or dermal infection is the more important one further observation must decide.

The duration of life of Ancylostoma duodenale, which is a specific parasite of man and has not been observed in other mammals, amounts to about five years, as strayed larvæ according to Looss wander for this extent of time in the body.

Cultivation of Larvæ.--(1) Mix the fæces (free from drugs such as salines or thymol) with animal charcoal, adding water if necessary till a consistence of porridge is obtained. If the stools are very fluid, allow to sediment first and pour off the fluid. The best charcoal is that made from bones, and should not have an acid reaction. Charcoal is necessary in order to prevent fermentation, which kills the larvæ. Spread in layers 2 to 3 mm. thick in Petri dishes. Incubate at room temperature. To extract the larvæ from the culture allow the surface thoroughly to dry, then pour on water; the larvæ wander out and are poured off and subsequently further purified by sedimentation or filtering through blotting paper, the larvæ passing through.

(2) A funnel is plugged with cotton wool, then filled with washed sand to within a centimetre or two of the rim. Stand this in a jar of water so that the level of the water is slightly below that of the sand. On the surface of the wet sand now place layers of blotting paper, and spread the fæces, diluted if necessary, on this in layers of a few millimetres thick (vide p. 474).

Detection of Eggs.--Vide p. 473.

Dermal Infection of Dogs.--Infection with larvæ of A. caninum. In two hours most of the larvæ are free in the cutis and in four hours in the subcutaneous tissue. By scraping a few days later the mucosa of the trachea large numbers of larvæ are found there.

*Ancylostoma ceylanicum*, Looss, 1911.

At the anterior edge of mouth capsule one large tooth; below or behind this towards the middle line a very small tooth, the tip only of which is seen. Male 5 mm. average. Lobes of bursa almost as long as broad, strongly projecting towards the ventral side. Rays short and relatively thick. Female 7 mm.

Habitat.--Intestine civet cat (Viverricula malacensis), Ceylon, and man in Bengal according to Clayton-Lane.

Other species are: A. caninum (Ercolani), in cat and dog, Europe and Africa; A. malayanum (Alessandrini), 1905, in the Malay bear (Helaretos malayanus); A. pluridentatum (Alessandrini), 1905, in Felis mitis, Brazil.

*Ancylostoma braziliense*, Gomez de Faria, 1910.

In cats (and dog), Brazil. Female 8·5 mm., male 7·5 mm. long. Eggs 65 µ by 32 µ. Leiper considers it to be identical with A. ceylanicum.

Group. *Bunostomeæ*, Railliet and Henry, 1909.

Bursa with median double, postero- and postero-external arising from a common trunk, posterior bifurcated, each limb bidigitate (fig. 336). Vulva in middle of body or a little in front. Uteri divergent.

Contains the following genera: (1) Bunostomum (= Monodontus); (2) Necator; (3) Bathmostomum; (4) Gaigeria.

Genus. *Necator*, Stiles, 1903.

Mouth capsule small, narrowed anteriorly (ventrally) by chitinous plates, as in Uncinaria. On each side of the base of the dorsal cone a lateral chitinous plate or lancet with smooth edge (not serrated), ventral lancets as in Ancylostoma. No ridges on outside of ventral wall. Aperture of dorsal œsophageal gland on tip of a cone projecting freely into the buccal capsule. Bursa closed. Posterior ray cleft to its root.

*Necator americanus*, Stiles, 1902.

Syn.: N. africanus, Harrison, 1910.

Male 8 mm. long, female 10 mm. The head is strongly bent dorsalwards so that almost by this character alone it can be distinguished from Ancylostoma duodenale. The buccal capsule is markedly small--in the male, 0·093 by 0·084 mm., in the female 0·11 by 0·097 mm. There are no teeth anteriorly on the ventral side of the capsule, but instead there are two cutting chitinous plates, the anterior portions of which are prominent and angular, and meet in the middle line in front. Posteriorly on each side the plate projects less, while between the anterior and posterior parts there is a deep angle. The inner (posterior) ventral lancets which also occur in A. duodenale are large, and project far into the lumen, the tips of these, of the lateral lancets, and of the dorsal cone almost meeting in the centre of the lumen. As already stated in the definition of the genus Necator, there are also lateral lancets which start from the base of the dorsal cone. This dorsal ridge, or rather in this case cone, is a striking object in the mouth, and projects right out into the cavity, and on its summit opens the dorsal œsophageal gland.

The bursa is about as long as broad, but has the lateral lobes strikingly lengthened, giving a trilobed appearance (fig. 336), but as in Ancylostoma duodenale it is closed on the ventral side. The distribution of the rays is best understood from the figure. The genital aperture lies on a marked conical protuberance; the cement gland is bilobed in transverse section. In the female the opening of the vulva is in front of the middle line, in A. duodenale it is behind.

The spicules, 0·92 mm. long are hooked at the extremity.

Eggs more pointed at the poles than those of A. duodenale, 64 µ to 72 µ by 36 µ, so that it may not be possible to distinguish single eggs owing to individual variations, yet on comparing a number they can be distinguished.

Geographical Distribution.--Brazil, Porto Rico, Cuba, Central Africa, East Africa, Victoria Nyanza, Gold Coast, Uganda, North-Western Rhodesia, Ceylon, Mysore. For other localities where A. duodenale is also found see p. 450.

Habitat.--In small intestine of man and gorilla (Troglodytes gorilla).

*Necator exilidens*, Cummins, 1912.

Syn.: N. africanus, Looss, 1911.

Male 7 mm., female 9 mm. long. The edges of the cutting plates are rounded, not angular, and do not meet in the middle line. Inner (posterior) ventral lancets very small. Lateral lobes of bursa broader than long. Rays thick and plump.

Habitat.--In the chimpanzee (Anthropopithecus troglodytes).

ANCYLOSTOMIASIS.

Morbid Anatomy.--Organs pale and bloodless. Abdominal organs sodden, and there is fluid in the serous cavities. Lungs: œdema. Kidneys: fatty changes, especially large pale kidney. Liver and heart also show fatty changes--there is much hæmosiderin in the liver cells. Blood: early stages, a leucocytosis 20,000 upwards, and eosinophilia 50 per cent. Later, anæmia (hydræmia). The number of worms found varies from ten to 1,000. They are rare in the duodenum, but occur as far as 6 ft. from the pylorus.

Group. *Syngameæ*, Railliet and Henry, 1909.

Bursa with anterior and median ray cleft; antero-external, close to median; postero-external, arising separately from posterior; posterior bifurcate to base, each branch bifurcate or trifurcate. Vulva in the anterior fourth of body. Uteri divergent.

Genus. *Syngamus*, von Siebold, 1836.

Head thickened, not tapering; broad mouth with gaping buccal capsule.

Male and female often in permanent copulâ.

Parasitic in respiratory passages of birds and mammals.

Habitat.--S. trachealis in poultry; S. bronchialis in goose; S. laryngeus in cattle; S. vasicola in goats, etc.

*Syngamus kingi*, Leiper, 1913.

Buccal capsules of male and female on same level. In S. trachealis and S. laryngeus, that of male in front of that of female. In S. dispar, that of male behind that of female. Œsophagus of male one-sixth, that of female one-ninth of total length. Mouth capsule in male and female terminal; it is dorsal in S. trachealis and in mammalian species. Tail of female bluntly pointed. Ovary reaches to anus. Excretory pore opposite the middle of the bulb of œsophagus. In S. trachealis it is opposite the œsophageal valves.

Habitat.--Found in sputum of patient by King in St. Lucia. Normal host probably a carnivore.

Family. *Physalopteridæ.*

Genus. *Physaloptera*, Rudolphi, 1819.

Mouth surrounded by two large lateral lips bounded posteriorly by a cuticular band projecting anteriorly, forming a collar. Each lip bears anteriorly and inwardly a cuticular appendage, the external tooth. Immediately below and internal to the external teeth the internal teeth, one on each lip. Each lip bears two large submedian papillæ. Tail of male with four pairs of pedunculated papillæ in a row on each side external to the six pairs of unpedunculated papillæ. Spicules unequal. Vulva in the anterior region of the body. Eggs with a characteristic thick smooth shell.

Parasitic in the intestine, more especially the stomach, of mammals (twenty species), birds (twelve species), reptiles (fourteen species).

*Physaloptera caucasica*, v. Linstow, 1902.

The male measures 14·2 mm. in length and 0·71 mm. in breadth; the bursa is broad, rounded off in front and narrower at the back; the right spicule measures 0·62 mm. in length, the left spicule 1·76 mm.; there are two papillæ in front of the orifice of the cloaca, four behind it and six unpedunculated on the tail. The female measures 27 mm. in length, 1·14 mm. in breadth; the caudal extremity is rounded off; the vulva is on the border of the first and second sixth of the length of the body; the eggs have thick shells, and measure 57 µ by 39 µ. It has hitherto only been observed once, by Ménétriés in the intestine of man (Caucasus).

*Physaloptera mordens*, Leiper, 1907.

Large worms resembling an immature Ascaris lumbricoides.

The inner lancet-shaped teeth have a sharp cutting edge towards the lumen. Below each is a cuticular boss projecting into the mouth (fig. 340).

Male 30 to 50 mm., bursa with four pairs of pedunculated papillæ, the second and third lying external to the first and fourth on each side. Spicules unequal, one slender (4·6 mm.), the other stouter (6 mm.).

Female 40 to 55 mm. Tail sharp. Vulva opens between the anterior fourth and fifth of the body. Eggs 43·6 µ by 35·3 µ with a thick smooth shell.

Habitat.--Œsophagus, stomach, small intestine of man (several cases). Nyasaland and Portuguese East Africa.

Family. *Ascaridæ*, Cobbold, 1864.

Sub-family. *Ascarinæ.*

Without œsophageal or intestinal diverticula; spicules without flanges.

Genus. *Ascaris*, L., 1758.

Intermediate lips and auricles absent. Lips edged with fine teeth. Lips triangular in cross section. Not grooved on internal surface.

*Ascaris lumbricoides*, L., 1758.

The colouring, in the fresh condition, is reddish-yellow or greyish-yellow; the body is of an elongated spindle shape. The oral papillæ are finely toothed. The dorsal papilla carries two sensory papillæ, the two ventral papillæ each one sensory papilla. The male measures from 15 to 17 to 25 cm. in length, and about 3 mm. in diameter; the posterior extremity is conical and bent hook-like ventrally; the spicules measure 2 mm. in length, are curved, and somewhat broadened at their free end; on each side around the orifice of the cloaca there are seventy to seventy-five papillæ, of which seven pairs are post-anal. The testicular tube is much folded, showing through the body integument, and is about eight times the length of the body. The female measures 20 to 25 to 40 cm. in length and about 5 mm. in diameter; the posterior extremity is conical and straight. The vulva is at the junction of the anterior and middle thirds of the body, which, at this point, has a slight ring-like constriction; the convoluted ovaries measure ten times the length of the body.

The ova are elliptical with a thick (4 µ) transparent shell (fig. 342) and an external albuminous coating which forms protuberances; the ova measure 50 µ to 70 µ in length, 40 µ to 50 µ in breadth; they are deposited before segmentation; the albuminous coating is stained yellow by the colouring matter of the fæces, but is sometimes absent. The egg cell is unsegmented, it almost completely fills the shell, and its nucleus is concealed by the large amount of coarse yolk granules.

Abnormal or unfertilized eggs also occur in fæces. They are distinguished by their elongated form (80 µ by 45 µ), irregularly cylindrical, its contents consisting of refractive granules.

Ascaris lumbricoides is one of the most frequent parasites of man; it is distributed all over the inhabited parts of the world, and though it is particularly frequent in the warmer regions, yet it also occurs in Finland, Greenland, etc. In temperate climates A. lumbricoides occurs most frequently in young children; it is, moreover, more common amongst country dwellers than amongst the inhabitants of towns, but is not lacking in infants, adults and aged persons. As a rule only a few specimens are present in the intestine, but many cases are known in temperate zones in which several hundreds of worms have been found in the same patient. This species is particularly numerous in the negroes of Africa and America. It occurs also in the monkey, dog and pig (? A. suilla).

The parasite was known in ancient times; the Greeks called it ἐλμινς στρογγύλη, Plinius termed it Tinea rotunda, later on it was named Lumbricus teres. The ἄσκαρις of the Greeks is our Oxyuris.

The small intestine is the normal habitat of Ascaris lumbricoides; the worms, however, often leave this part of the intestine and wander into the stomach, whence they are frequently evacuated by vomiting, or they may creep through the œsophagus into the pharynx and crawl out through the nose or mouth; very rarely they may find their way into the Eustachian tube or into the naso-lachrymal duct, or into the excretory ducts of the liver and pancreas; exceptionally they may gain the trachea, and they have also been found in the abdominal cavity. They may bore through adhesions between the intestinal wall and the omentum (worm abscess); they occasionally penetrate the urinary apparatus and are passed with the urine; in febrile diseases A. lumbricoides usually leaves the intestine spontaneously. It is obvious that these wanderings may be accompanied by the most serious symptoms, but in sensitive persons the invasion of even only a few intestinal Ascarides gives rise to a series of almost inexplicable symptoms (hysterical, epileptiform attacks, cerebral congestion, aphonia, etc.), which cease with the expulsion of the worms, so that many authors are driven to the conclusion that these Ascarides secrete a toxin. Fortunately, the presence of A. lumbricoides in the intestine is easily demonstrated by the microscopical examination of the fæces.

Development.--Several authors (Gros, Schubart, Richter, Leuckart and Davaine) have demonstrated that the ova of Ascaris develop in water or moist earth after a long period of incubation. Freezing and desiccation (if not too long) do not injure their powers of development; the duration of the development depends on the degree of the surrounding temperature. At a medium temperature, after a varying period of incubation, it takes from thirty to forty days for the embryo to become formed. The spirally rolled up embryo, with its so-called “tooth,” formed by three papillæ close together, never leaves the egg-shell in the open, even if the eggs are kept for years under favourable conditions. Davaine proved that the larvæ hatch out in the intestine of the rat, but are again expelled with the fæces; he therefore concluded that the hatching likewise takes place within the intestine of man, but is followed by the invasion of the larvæ. In the meantime Leuckart had sought to infect himself by swallowing embryo-containing eggs, but without results; he therefore conjectured that there must be an intermediary host, and v. Linstow thought he had found it in myriapods (Julus guttulatus). Subsequently, Davaine’s opinion proved correct. First of all Grassi succeeded in infecting himself by swallowing 100 embryo-containing eggs of Ascaris lumbricoides; five weeks after ingestion the worms had attained maturity and their ova appeared in the fæces. Calandruccio also sought to infect himself, but failed, yet he succeeded in infecting a little boy aged 7. Lutz also reports a successful experiment which must have been positive, as young worms 5·5 to 18 mm. long were expelled. Lutz proved that the eggs lost their albuminous shell by long lying in water and then died when introduced into the stomach; this would explain the failure of Leuckart’s experiment; in moist earth the albuminous shell is retained. Finally, Epstein conducted unimpeachable experiments on three children which place direct infection with embryo-containing eggs beyond doubt; he, moreover, proved that the development of the eggs takes place more rapidly in the fæces when there is free admission of air, sun, and a sufficiency of moisture.

Accordingly, infection occurs partly through water, but principally direct from the soil.

*Ascaris*, sp.

Wellmann states that yet another species of Ascaris in man occurs in the highlands of Angola: up to the present nothing certain is known about it (Welland, “Critical Notes on Tropical Diseases of the Angola Highlands,” New York Med. Journ. and Philadelphia Med. Journ., August 12 to September 2, 1905.)

*Ascaris texana*, Smith et Goeth, 1914.

Female alone known; 58 to 60 mm. and upwards in length; characterized by the serration of the anterior border of the lip and by the appearance of interlabia. Evacuated by a white settler in Texas. Position of this worm doubtful.

*Ascaris maritima*, Leuckart, 1876.

Only one immature specimen, a female (43 mm. in length and 1 mm. in breadth), has hitherto been described, and it was vomited by a child in North Greenland in 1865. (R. Leuckart, “Die menschlichen Parasiten,” 1876, edition 2, i, p. 877.)

Genus. *Toxascaris* (τόξον, an arrow), Leiper, 1907.

Body anteriorly bent dorsally, cuticle finely striated. Œsophagus without a distinct bulb. Tail of male tapers to a point. Testis in anterior portion of posterior half of body. Vulva about middle of body. Eggs oval and smooth.

*Toxascaris limbata*, Railliet and Henry, 1911.

Syn.: Lumbricus canis, Werner, 1782; Ascaris teres, Goeze, 1782; Ascaris cati et caniculæ, Schrank, 1788; Ascaris canis et felis, Gmelin, 1789; Ascaris tricuspidata et felis, Bruguiere, 1791; Ascaris werneri, Rud., 1793; Fusaria mystax, Zeder, 1800; Ascaris marginata et mystax, Rud., 1802; Ascaris alata, Bellingham, 1839.

Striations 6 µ to 12 µ apart. Cephalic wings long, narrow, semi-lanceolate. Male, 4 to 6 cm. Spicules, 1,002 µ and 1,005 µ. Female, 0·5 to 10 cm. Eggs, 75 µ to 85 µ, shell thick and smooth. Host: dog, occasionally man.

Genus. *Belascaris* (Βέλος, an arrow), Leiper, 1907.

Body anteriorly bent ventrally, cuticle coarsely striated. Œsophagus with a distinct bulb. Tail of male conical. A papillæ-bearing protuberance behind the anus. Testis in anterior half of body. Vulva in anterior part of body. Eggs corrugated.

*Belascaris cati*, Schrank, 1788.

Syn.: Belascaris mystax, Leiper, 1907; Ascaris mystax.

Striations 12 µ to 16 µ apart. Cephalic wings lanceolate. Male 3 to 6 cm. Spicules 17 to 1·9 mm. Female 4 to 10 cm. Eggs, 65 µ to 75 µ in diameter, surface finely honeycombed. Host: domestic cat, and man, eight or nine cases.

*Belascaris marginata*, Rudolphi, 1802.

Striations 16 µ to 22 µ apart. Cephalic wings long, narrow, semi-lanceolate. Male, 5 to 10 cm. Spicules, 750 µ and 950 µ. Female, 9 to 18 cm. Eggs, 75 µ to 80 µ. Shell finely honeycombed. Host: dog.

Genus. *Lagocheilascaris*, Leiper, 1909.

Thick lips separated by a furrow from the body; between the lips small intermediate lips without “pulp.” The cutting angle of each lip bifurcated. Along each lateral line a cuticular wing extending the whole length of the body. Eggs, thick shell with a mosaic pattern.

*Lagocheilascaris minor*, Leiper, 1909.

Male, 9 mm., tail sharply curved. Spicules colourless, 3·5 and 4 mm. long. More than twenty-four pairs of pre-anal papillæ, at least five pairs of post-anal. Female, 15 mm. Straight posteriorly. Vulva 6 mm. from head with two lips. Eggs, 65 µ in diameter. Host: man, cutaneous abscesses. Trinidad.

Family. *Oxyuridæ.*

Genus. *Oxyuris*, Rudolphi, 1803.

Mouth unarmed. The three labial papillæ are only slightly protuberant, the œsophagus is long and presents two well-marked bulbs. The vulva is in the anterior part of the body.

*Oxyuris vermicularis*, Linnæus, 1767.

Syn.: Ascaris vermicularis, L.; Fusaria, Zeder, 1803.

Colour white, the striated cuticle forms projections at the anterior end which extend some distance back along the middle of the ventral and dorsal surfaces; the longitudinal lateral flanges of the skin corresponding to the lateral lines are well seen in transverse sections; there are three small retractile labial papillæ around the mouth. The male measures 3 to 5 mm. in length, and shortens on death; the posterior extremity of the body is curved ventrally and presents six papillæ. Spicule 70 µ long, hook-like. The female is 10 mm. in length and 0·6 mm. in diameter; the anus is about 2 mm. in front of the tip of the tail; the vulva is in the anterior third of the body; the eggs are oval, asymmetrical, with double-contoured shells, and measure 50 µ to 55 µ by 16 µ to 25 µ; they are deposited with clear, non-granular tadpole-like embryos already developed.

Habitat.--Adults in large intestine of man. Young forms in small intestine and often in the appendix.

The worm lives in the lower part of the small intestine, cæcum and vermiform appendix, and before becoming adult undergoes two or three moults (Heller). According to Wagener the worms at times live in the gut wall, giving rise to calcareous nodules. When the uterus of the fertilized females begins to fill with eggs they leave the cæcum and travel through the colon to the rectum. The uterus is now packed with eggs which contain a tadpole-shaped embryo. Egg-laying now takes place, partly in the rectum, partly outside, the mode of exit being not only passive through defecation but also an active one on the part of the worms when the patient is in bed. In this case the worms crawl out of the anus, producing a most intolerable itching as they scatter their eggs between the nates and the perinæum. From here in the case of girls they may get occasionally into the vulva and vagina, and even into the oviducts and so into the body cavity. The worms also may wander through the alimentary canal in the opposite direction, getting out occasionally through the mouth. Recently a rôle has been assigned to them, as to other gut parasites, in appendicitis and typhlitis.

It is stated that the males die after fertilizing the females, thus explaining why they are so rarely met with in fæces [but it is probable that they often escape notice from their small size.--J. W. W. S.].

Development.--The eggs, which often adhere together, contain a tadpole-like embryo, the thin tail of which is bent upwards ventrally; the embryo in a short time, given a sufficiently high temperature, passes into a second folded nematode-like embryonal stage, lying in the egg-shell, either in the fæces, with which also numerous females pass out, or in the moisture of the groove between the buttocks, and they there await the opportunity of being reintroduced into man per os. It is very improbable that infection takes place directly in the large intestine, as is occasionally stated, because although the harbourers of Oxyuris are frequently liable to auto-infection, this takes place exclusively through the mouth, and is conveyed by the fingers, on which the ova of Oxyuris, and occasionally the female worms, have clung.

The opportunity for this is afforded every evening, as naturally the troublesome itching caused by the wandering of the worms is met by scratching and rubbing with the fingers. It is therefore possible that the eggs may even thus be introduced into the nose, where the young Oxyuris are perhaps hatched out, if they get high enough up on the moist pituitary mucous membrane. As a matter of fact, the larvæ of Oxyuris have been found in the nose. Moreover, one can understand that the eggs of Oxyuris are transferred from person to person by the hand, directly or indirectly. This again explains the wholesale infections which occur in collective dwellings, after a person harbouring Oxyuris has been admitted into boarding-houses, etc. The primary infection may be also caused in other ways--by foods, fruits, vegetables and other articles that are eaten raw, and are polluted with the ova. Perhaps also flies or their excrement play a part in the distribution of the parasite, similar to that demonstrated by Grassi as taking place in the spread of the ova of Trichocephalus and Tænia.

The assumption of a direct development without an intermediary host was first substantiated by Leuckart by experiments on himself and three of his students; about fourteen days after swallowing the eggs the Oxyuris has attained 6 to 7 mm. in length; Grassi, and later on Calandruccio, infected themselves by swallowing adult female Oxyuris, with the same results. Heller found worms in the gut (appendix vermiformis) of a male child five weeks old.

Other species are: O. compar in the cat; O. curvula and O. mastigodes in horse, ass, mule; O. ambigua in the rabbit; O. poculum in the horse; O. tenuicauda in the horse. Many species occur in insects, especially in Blattidæ and Hydrophilidæ (aquatic beetles).

Family. *Mermithidæ.*

Genus. *Mermis*, Dujardin, 1845.

With characters of the family.

*Mermis hominis oris*, Leidy, 1850.

Fourteen centimetres in length, 0·16 mm. in breadth; mouth terminal; posterior extremity obtuse and provided with a recurved hook 50 µ long.

The parasite was “obtained from the mouth of a child.” Stiles considers it to be probably a Mermis, possibly swallowed in an apple.

*Agamomermis*, Stiles, 1903.

Group name for immature Mermithidæ.

*Agamomermis restiformis*, Leidy, 1880.

This worm measures 65 cm. in length, pointed anteriorly, the posterior extremity broadened and rounded off (1·5 mm. in breadth); the mouth is terminal, without lips. Behind the mouth six papillæ; the œsophagus measures 1·125 mm. in length; the intestine appears to terminate blindly.

This parasite was obtained in West Virginia from the urethra of a young man, aged 20, who for a few days previous to expelling the worm passed turbid and bloody urine.

TECHNIQUE.

PRESERVATION AND EXAMINATION OF FLUKES.

Fixation.--(Method A.) (1) Place the flukes in a test tube or small bottle a quarter full of normal saline. Shake the contents as hard as possible (the object of this is to extend the flukes) for half a minute.

(2) Add immediately an equal bulk of saturated aqueous solution of corrosive sublimate and shake again as vigorously as possible for a few minutes.

(3) Transfer when convenient to 70 per cent. alcohol. (Before staining and mounting remove the sublimate with tincture of iodine.)

(Method B.) In case of large flukes, e.g., Fasciola hepatica, Fasciolopsis buski, compress the flukes between two glass slides with rubber bands or thread. Fix in sublimate or in absolute alcohol, or in 10 per cent. formalin.

(Method C.) Place the flukes in 10 per cent. formalin solution.

Staining is successfully effected by using quite dilute solutions of carmine or hæmatein overnight. This is far preferable to using strong solutions, as it may be almost impossible to remove a too intense stain. Almost any dilute carmine solution suffices. One of the best is acetic-alum carmine (boil excess of carmine in a saturated aqueous solution of potash-alum for about fifteen minutes; add glacial acetic acid to the extent of 10 per cent.; let it stand for a week; filter). For use, dilute about thirty times with water. Place the flukes directly in the stain. Stain overnight or longer.

Differentiation.--In order to get the sharpest picture, it is best now to differentiate (but this may often be omitted) with acid alcohol (70 per cent. alcohol 100 parts, HCl 5 drops). Allow to act from one to twenty-four hours, according to the appearance of the flukes. Similarly, in staining with hæmatoxylin solution, dilute twenty to thirty times so that the water is merely tinged with the stain. Differentiate as before. After staining, dehydrate, clear, and mount in balsam if required.

Clearing and Mounting.--(1) Carbolic acid (carbolic acid 94, water 6) is a very convenient clearing agent. It may be used for stained or unstained specimens. It will clear rapidly without previous dehydration. If it is required to mount a specimen permanently, transfer from carbolic to alcohol, then cedar-wood oil (or xylol, etc.), then balsam.

(2) Creasote.--Dehydrate the specimen, stained or unstained, transfer to creasote. If it is desired to mount permanently, transfer back to alcohol, then cedar-wood oil, then balsam.

(3) Cedar-wood Oil.--Preferable to xylol or oil of cloves. Dehydrate the specimen in alcohol. To mount permanently, transfer to balsam.

(4) Glycerine.--Vide under methods of preservation of ova; to mount permanently, transfer to glycerine jelly; subsequently to harden the jelly, expose to formalin vapour.

Of these media, carbolic acid has the greatest refractive index excepting that of balsam. The latter may, in some cases, render structures too transparent, and it may be advisable to use only glycerine or glycerine jelly.

PRESERVATION OF OVA IN FÆCES, URINE, BILE, ETC.

Heat some 70 per cent. alcohol in a basin to about 60 to 70° C. (until bubbles begin to appear). Add the fæces, etc., in the proportion of one part to about nine of fixative; keep stirring. Allow the sediment to settle. Transfer to a bottle with some fresh 70 per cent. alcohol.

Transference to Glycerine.--Prepare 5 per cent., 10 per cent., 20 per cent. solutions of glycerine in 70 per cent. alcohol. Pour off the alcohol in the bottle of fæces, etc., and replace by 5 per cent. glycerine solution. Allow to stand an hour or so. Then in the same way replace the 5 per cent. by a 10 per cent. glycerine, and finally by a 20 per cent. glycerine solution. When in this latter expose freely to the air (protecting from dust), so as to allow the alcohol and water to evaporate. Add a few drops of glycerine from time to time till eventually the ova are in pure glycerine. (In a very moist climate it may be necessary to use lime or calcium chloride to dry the air.) To mount permanently transfer some of the sediment to glycerine jelly.

PRESERVATION AND EXAMINATION OF CESTODES.

Fixation.--(1) Saturated aqueous corrosive sublimate.--Add to this glacial acetic acid to the extent of 1 per cent. (Note this fixative will dissolve the “calcareous corpuscles”; 10 grammes of sublimate to 160 c.c. of water will give a saturated solution.) Warm the fixative to 70° to 80° C. (Avoid the use of needles.) Use plenty of fixative. Allow to act for a quarter of an hour or so. (a) Transfer to 70 per cent. alcohol. (It is advisable to remove the sublimate by the use of Lugol’s solution, or a solution containing tincture of iodine, adding this until the iodine colour is permanent.) Or (b) transfer for preservation to 10 per cent. formalin.

Or (2) 10 per cent. formalin.--In order to prevent contraction it is advisable to extend the tapeworm and keep it fixed by glass plates, or wind the worm around a wide glass tube or bottle, and then fix it.

Or (3) fix in hot alcohol.

Staining.--As under flukes. It is necessary to sacrifice portions of the tapeworm for this purpose, cutting out, e.g., mature segments, so as to study the topography of the genitalia.

Clearing.--As under flukes. To examine the hooks satisfactorily it is best to cut off the head with a sharp knife and mount. A certain amount of pressure is then advisable in order to view the hooks completely so as to measure them.

PRESERVATION OF OVA IN FÆCES, ETC.

As under flukes.

PRESERVATION AND EXAMINATION OF NEMATODES.

Fixation.--(1) Thoroughly wash the worms to get rid of mucus, etc., by shaking up in warm saline (or water) till the washings are clean. Then transfer to 70 per cent. alcohol heated to about 70° C. It is absolutely necessary to use hot fixatives in order to extend the worms. If no alcohol or spirit is immediately available, drop the worms into hot water, or saline, and transfer later to 70 per cent. alcohol.

(2) Drop into hot 10 per cent. formalin.

Clearing.--(1) Carbolic acid, vide p. 471.

(2) Creasote, vide p. 471.

(3) Glycerine, vide p. 472.

Staining.--In case of quite small Nematodes, e.g., Anguillulidæ, carmine may be used, but as a rule staining is not advantageous.

Rolling.--In order to study the mouth parts, or bursa, etc., it is necessary to place the worm in any desired position. This is done as one would roll a penholder along the table by one’s finger placed on top of it. In the case of a worm, one edge of the cover-glass is placed over the worm, the other is supported by a strip of cardboard. By tapping the cover-glass the worm will now revolve as much as required provided it is round and straight. In certain cases it may be necessary for this purpose to cut off the head or tail. Roll these separately.

When a suitable position is got, the worm may be fixed in this position by pressure on the cover-glass, so as slightly to flatten it.

Mounting the Head.--If it is required to get an end view, it is necessary to cut off the head transversely as near the end as possible, and then mount.

Detection of Eggs (Bass and Hall).--Mix the fæces thoroughly with ten times the volume of water. Filter through gauze. Centrifugalize the filtrate. Wash the sediment and centrifugalize. Repeat twice. To sediment add CaCl_{2} solution, sp. gr. 1250. The eggs float to surface. Pour off surface fluid. Dilute to sp. gr. 1050. Centrifugalize. Examine sediment, which contains practically all the eggs in the stool.

Detection of Small Nematodes.--Mix the fæces thoroughly with water. Allow to settle for five minutes. Carefully decant off, or better, syphon off the fluid. Mix the sediment again with water. Allow to settle. Remove the fluid. Repeat several times. Examine the sediment in a Petri dish. As the fluid is poured off, the worms will be seen collected in the backwater. Remove them with a brush. Fix in hot 70 per cent. alcohol.

CULTIVATION OF LARVAL FORMS OF ANCYLOSTOMA AND STRONGYLOIDES.

A modification of the second method of Looss (p. 455) is that of Fülleborn. A glass filter funnel is lined with linen or with cotton wool dyed black with iron-tannin. On this is placed a layer of sterile sand, and on top of this the fæces. The whole is moistened. The larvæ hatch out and wander through the meshes of the wool, appearing on the edges of the same as white threads visible to the naked eye. With a platinum needle these can be easily removed. The glass filter can be placed on a glass cylinder, and this in another large stoppered cylinder containing caustic potash solution at the bottom, so that any larvæ escaping from the funnel are killed.

D. *ACANTHOCEPHALA*, Rud.

Gutless, nematode-like worms that carry at their anterior end a retractile rostrum beset with hooks. In their adult condition they only live in vertebrate animals. During their larval stage they are often parasitic in invertebrate animals.

The Acanthocephala are elongated cylindrical worms, with a rounded posterior end. In some species an annulation is distinctly recognizable; they are, however, not segmented. The size varies according to the species, between about 5 to 10 mm. and 40 to 50 cm.; in general, however, there is a preponderance of the small species. The sexes are separate, and the males can easily be distinguished from the females without examination of the genitalia, as the females are both larger and thicker.

The body wall of Echinorhynchus is limited by a thin cuticle, which is attached inwardly to the hypodermis. In only exceptional cases a syncytium with large nuclei, even in the adult condition, is represented by the hypodermis; and in it fibre systems, the elements of which run in layers in various directions, appear, and it is only towards the interior from these strata of fibres that the nuclei of the hypodermis are found. As a rule, these fibres, at all events the radiary fibres, are regarded as muscles. Hamann describes them as elastic fibres, which lie in a viscid gelatinous connective substance (transformed protoplasm?); a lacune system filled with a granular fluid, the central part of which are two longitudinal lacunes lying at the sides, also belongs to the cutaneous strata, as do the so-called lemnisci, two short, flat organs suspended in the body cavity, and the pedicles of which are attached anteriorly at the border between the rostrum and body; their structure as well as their origin permit them to be traced to the skin (fig. 348A).

Finally, inwardly below the skin there follows a layer of annular, and after these a layer of longitudinal muscles, the structure cells of which remain present in the residues, carrying nuclei. The motor apparatus of the rostrum, the sheath of the rostrum, and the lemnisci also belong to the muscular system. The rostrum represents a finger-shaped hollow process of the cutaneous layer; but, according to Hamann, it originates from the entoderm and passes through the skin secondarily. It is covered by a thin cuticle, and as a rule contains a large number of regularly placed chitinous hooks that adjoin a granular formation tissue. From the base of the rostrum springs a tubular hollow muscle extending into the body cavity; this is the RECEPTACULUM PROBOSCIDIS, from the base of which again bundles of longitudinal muscles originate, which pass along its axis and that of the rostrum itself, and are inserted at the inner surface of its anterior end (RETRACTOR PROBOSCIDIS). These muscles when they contract invaginate the proboscis and draw it into the receptaculum; when reversed they act again as PROTRUSOR PROBOSCIDIS. The whole of the anterior body, however, can be invaginated, and for this purpose there is a muscle that originates from the body wall at a variable distance back, and which is joined to the receptaculum (RETRACTOR RECEPTACULI); there is also a bell-shaped muscle which springs from the body wall behind the lemnisci in rings, and passes forward to the spot of attachment of the lemnisci.

The nervous system consists of a cluster of ganglia situated at the base of the rostrum, from which three nerves pass towards the front and two towards the back. No sensory organs are known.

The excretory organs, according to Kaiser, lie at the upper border of the ductus ejaculatorius in the male and at the so-called bell in the female. Here they represent the long-known villous tufts, placed on disc-like cushions. In each of the cylindrical villi--which terminate blindly towards the body cavity--there lies a cilium, which springs from the membrane lining the villus, and which lies in a space cavity of the villus, which ultimately proceeds as a little canal. There are three canals discharging into the uterus that serve to conduct the excretory materials from the body cavity; special glandular cells corresponding to the terminal cells of the Platyhelminths, at the commencement of the system, are not present in the Acanthocephala.

SEXUAL ORGANS.

(a) Male Organs.--The greatest part of the male genital apparatus is contained in a muscular sheath--the ligament--which originates at the posterior end of the receptaculum proboscidis, passes along longitudinally through the body cavity, and is inserted at the posterior end of the worm. The two oval testicles usually lie one behind the other; their vasa efferentia unite sooner or later into a vas deferens which passes backwards, and finally terminates in the penis; the terminal portion of the conducting apparatus is surrounded by six large glandular cells (prostatic glands) the excretory ducts of which open into the vas deferens. The penis itself is placed at the base of a bell-shaped invagination of the posterior end, the bursa, which is everted during copulation.

(b) Female Organs.--There are only two ovaries present in the ligament during the larval stage. During the course of growth they divide into accumulations of cells (placentulæ, loose or floating ovaries), which finally cause the ligament to burst and they thus attain the body cavity. Thence a peculiarly constructed apparatus finally conveys the eggs out. This apparatus consists of the uterine bell and vagina, the latter discharging at the posterior extremity of the body. The bell is a muscular canal provided with apertures at both the anterior and posterior extremities. Its interior space is in direct communication with the body cavity, and the anterior orifice takes up all materials floating in the cavity--egg-balls, mature and immature eggs--and pushes these further backwards. The continuation of the bell lumen is now narrowed by a number of large cells in such a manner that only bodies of a certain form can pass through this tract and attain the uterus; everything else is conveyed back into the body cavity through the posterior opening of the bell.

The eggs are already fertilized in the body cavity, and in this position go through their development to the formation of the embryo. Completely developed eggs are surrounded by three shells, and are generally fusiform. The eggs agglomerate in masses in the uterus until they are finally deposited through the vagina and vulva. For the further development, the transmission of the eggs into an intermediary host--usually a crustacean or an insect--is necessary; the metamorphosis is very complicated; but this transmission may be very easily effected artificially by feeding suitable crustaceans (Asellus, Gammarus, etc.) with the eggs of Acanthocephala; this being the only method of inducing the larva to hatch out so that its structure may be studied. The larva appears in the form of an elongated, somewhat bent body, at the stumpy anterior end of which there is a crown of hooks or spines, whereas the posterior end is pointed. Especial retractors draw in the hook-beset anterior surface, and an elastic cushion beneath them jerks them forward again when required. In the middle of the body a roundish heap of small cells is seen, from which the entire body of the Echinorhynchus originates, even to the cutaneous layer; the latter is also the larval skin in which the small Echinorhynchus gradually grows. The development of all the organs takes place within the intermediary host, and the parasite only needs to be imported into the terminal host to attain the adult stage after a certain growth. In some cases, however, a second intermediary host is utilized.

Species of Acanthocephala only occur exceptionally in human beings.

*Echinorhynchus gigas*, Goeze, 1782.

Syn.: Tænia hirudinacea, Pallas, 1781.

The body is elongated, gradually decreasing in thickness towards the back. The rostrum is almost spherical, and is beset with five or six rows of recurved hooks. The males measure 10 to 15 cm. in length, the females 30 to 50 cm.; the eggs are provided with three shells, of which the middle one is the thickest. The eggs measure 0·08 to 0.1 mm. in length. The GIANT ECHINORHYNCHUS occurs especially in the intestinal canal of the domestic pig; it is less common in other mammals. It bores deep into the mucous membrane with its rostrum, and causes an annular proliferation around the perforated spot; occasionally also it causes perforation of the intestine.

It is doubtful whether the giant Echinorhynchus occurs in man. Leuckart admitted that there were a few positive cases. According to Lindemann, Ech. gigas occurs in human beings in South Russia, and its presence is not rare. This statement, however, has not been confirmed. Its presence in man is by no means impossible, as its intermediary host, the cankerworm, or cock-chafer (Melolontha), is, according to Schneider, occasionally eaten raw by human beings. According to Kaiser, the golden beetle (Cetonia aurata) and, according to Stiles, another beetle in America (Lachnosterna arcuata) are also intermediary hosts.

*Echinorhynchus hominis*, Lambl, 1859.

This term is applied to an ECHINORHYNCHUS found by Lambl in the intestine of a boy who had died of leucæmia; the worm was 5·6 mm. in length, and the almost spherical head was beset with twelve transverse rows of hooks.

*Echinorhynchus moniliformis*, Bremser, 1819.

The male is 4 cm. in length, the female 8 cm. long. This species lives in the intestine of field-mice, rats, marmots and Myoxus quercinius. A beetle (Blaps mucronata) is the intermediary host.

This species has also once been artificially cultivated in man (Grassi and Calandruccio).

E. *GORDIIDAE.*

Very long thin worms similar to Filariæ, which, in their adult condition, live free in brooks, pools and springs; the mouth and the commencement of the intestine are obliterated; there are no lateral ridges, and the muscular system presents a structure different to that of the Nematoda. The posterior end of the male is split, and spicules are lacking; there are two testicles. In both sexes the genitalia discharge through the terminal gut.

The larvæ, which carry a rostrum beset with hooks, force themselves into the larvæ of water-insects; more rarely they invade molluscs, and they then become encysted within the body of the host. According to Villot, at least a part of them attain the intestine of fishes, where they again become encysted, and after a period of rest they travel into the tissues of their hosts, and finally again reach the exterior by way of the intestine, where they then become adult. In most cases, however, the gordius larvæ are taken up by predacious water insects; they live for a while in the body cavity of these insects, undergo a metamorphosis, and finally wander into the water.

A few species invade man accidentally with water, in which case they are usually vomited up:--

Gordius aquaticus, Dujardin, 30 to 90 cm. in length (Aldrovandi, Degland, Siebold, Patruban).

Gordius tolosanus, Duj., 11 to 13 cm. in length (Fiori).

Gordius varius, Leidy, 10 to 16 cm., female, up to 30 cm. in length (Diesing).

Gordius chilensis, Blanch. (Guy). Gordius villoti, Rosa (Bercutti, Camerano); Gordius tricuspidatus, L. Def. (R. Blanchard), Gordius violaceus, Baird (Topsent), and Gordius pustulosus, Baird (Parona).

F. *HIRUDINEA s. DISCOPHORA* (Leech).

The Hirudinea, which have been appropriately included amongst the Annelida, differ in many respects from the typical members of the group; their body is long and flat, it lacks the parapodia that are characteristic to all forms of Annelida; but, on the other hand, possesses a terminal posterior sucker, and in many species there is also an anterior sucker. The mouth is terminal at the anterior end, the anus lies dorsally above the posterior sucker (fig. 348D). The body is segmented, but this is less manifest in the body covering than it is in the arrangement of the internal organs; the segmentation, nevertheless, is also indicated exteriorly by the appearance of the cutaneous sensory organs which correspond to the segments. This shows what the condition of the ganglia in the abdominal ganglion chain has taught us, that the anterior and the most posterior segments are considerably abbreviated--a part of the latter taking part in the formation of the suctorial organs. In a great many species the skin is distinctly annulated, four or five of such rings, at least in the central region of the body, appearing on one segment of the body. The condition of their body cavity is another peculiarity of the Hirudinea; it is narrowed by the powerful development of the connective tissue and the muscular system into four tubular sinuses, which have the appearance of blood-vessels. There are usually one dorsal and one ventral median trunks, as well as two lateral trunks; in addition, a particular blood-vessel system exists.

The skin consists of a very thin cuticle that is cast off from time to time; it is secreted by the underlying cylindrical epithelium, which contains numerous goblet cells. The muscular system is strongly developed; it consists of long tubular fibres, which run circularly, longitudinally and in the dorso-ventral direction; the muscular system is subject to a particular expansion in the clinging organs and at the commencement of the intestine. On the whole, the alimentary canal represents a tube running straight from the mouth to the anus, which possesses a number of blind sac-like protuberances at the sides varying according to the species. The most anterior section, the pharynx, in the leeches with maxillæ carries three chitinous, semicircular plates furnished with teeth--the jaws--which serve to tear up the epidermis in order to open the blood-vessels; in the leeches with rostra a long protractile proboscis rises from the base of the elongated pharynx. Numerous salivary glands, the secretion from which possesses toxic properties, discharge into the pharynx. The œsophagus, which follows the pharynx, and to the exterior of which numerous radiary muscles are fixed, is a suctorial organ in its entire structure. The nutriment in the larger species consists of the blood of vertebrate animals, in smaller species and in the young stages the food consists of small invertebrate animals.

The NERVOUS SYSTEM exhibits the typical structure of other segmented worms; the sensory organs consist of the previously mentioned goblet-shaped cutaneous sensory organs, of the organs of taste, and of eyes, the latter frequently being present in large numbers.

The EXCRETORY or segmental organs exhibit many peculiarities, which cannot, however, be detailed here. They commence with funnels in the lacunes of the body cavity, and usually discharge on the ventral surface.

Almost all the Hirudinea are hermaphrodite and copulate reciprocally. The two ovaries are very small, and the oviducts that proceed from them soon unite into a common duct, which then passes into the uterus and discharges through the short vagina in the median line of the ventral surface behind the male organs into the so-called clitellar region. The male sexual apparatus consists of symmetrically arranged testicles, varying in number according to the species, the short vasa efferentia of which, one by one, run into the vas deferens, passing towards the front on each side. In front, at about the level, or a little in front, of the female genitalia, the two vessels pass into a convoluted mass of tubes to the so-called epididymis, and then discharge into the single protractile penis (fig. 348D).

All leeches deposit so-called COCOONS. These are small barrel-shaped or pouch-like bodies, which are surrounded by a thicker shell and contain a number of eggs in a large mass of albumen; the albumen originates from glands of the generative organs, the shell substance from cutaneous glands of the clitellar region.

Family. *Gnathobdellidæ* (Leeches with Jaws).

These are distinguished by the possession of usually three jaws in the pharynx; the body consists of twenty-six segments. The posterior sucker is large and flat; the anterior sucker is smaller. The Hirudinea have five pairs of eyes, the Nephelinæ have four pairs.

Genus. *Hirudo*, L., 1758.

The entire body consists of 102 annulations, five appearing on one segment in the central region of the body. The pharynx has three semicircular jaws, the arched border of which is beset with numerous teeth (50 to 100). The male sexual orifice lies between the thirtieth and thirty-first rings, the female orifice between the thirty-fifth and thirty-sixth. There are numerous species, some of which are utilized for medicinal purposes.

*Hirudo medicinalis*, L., 1758.

It occurs in numerous colour varieties, one of which has been designated Hirudo officinalis, Moq.-Tandon. Usually the dorsal surface is greyish-green and is marked with six rusty-red longitudinal stripes. The ventral surface is olive-green, more or less spotted with black, and marked at the sides with a black longitudinal line. The length averages 8 to 12 to 20 cm. This leech lives in swamps, ponds and brooks, overgrown with plants and having a muddy bed. The cocoons are deposited in the soil at the sides. Europe, as well as North Africa, is its home. At the present day it has been exterminated from most parts of Central Europe, but it is still very common in Hungary. Its use for medicinal purposes is well known. A large leech can suck about 15 grs. of blood, and about the same amount is lost through secondary hæmorrhage.

*Hirudo troctina*, Johnston, 1816.

Syn.: Hirudo interrupta, Moq.-Tandon, 1826.

This species measures 8 to 10 cm. in length. The back is greenish, with six rows of black spots surrounded by red; the lateral borders are orange-coloured; the abdomen spotted or unspotted. Its habitat is in North Africa and Sardinia. It is applied medicinally in England, Spain, France, Algeria, etc.

Genus. *Limnatis*, Moq.-Tandon, 1826.

Nearly related to Hirudo, but is differentiated by a longitudinal groove on the inner surface of the upper lip of the anterior sucker. The jaws are furnished with over 100 very sharp toothlets.

*Limnatis nilotica*, Savigny, 1820.

Syn.: Bdella nilotica, Sav.; L. nilotica, Moq.-Tandon; Hæmopis (vorax), Moq.-Tandon, 1826, p. p.; Hæmopis sanguisuga, Moq.-Tandon, 1846 (nec Hir. sanguis, Bergm., 1757).

This species measures 8 to 10 cm. in length, and becomes gradually more pointed towards the front; the body is always soft. The back is brown or greenish, and has usually six longitudinal rows (rarely only two or four) of black dots. The abdomen is dark; but numerous colour variations occur.

The native place is North Africa, especially the coastal regions; it is also found in the Canaries, the Azores, Syria, Armenia, Turkestan, perhaps also Southern Europe. It is taken into the mouth with drinking water, and may settle in the pharynx, larynx, œsophagus, and nasal cavities of human beings. This species has also been observed in the vagina and on the conjunctiva. It is equally fond of attacking domestic animals.

Hirudo mysomelas (Senegambia) and Hirudo granulosa (India) are placed with this genus, and, like our leech, are also used for medicinal purposes.

Genus. *Hæmadipsa*, Tennent, 1861.

These leeches live on land, and measure 2 to 3 cm. in length. About a dozen species are known. They are a veritable scourge to persons in the tropics (Asia, South America), as they attack them to suck their blood. They are able to force their way even under close-fitting garments, so that it is difficult to protect oneself from their assaults (Hæmadipsa ceylonica, Bl., and other species).

Family. *Rhynchobdellidæ* (Leeches with Rostrum).

These are furnished with a proboscis in lieu of the jaws; the segment consists of three annulations.

Genus. *Hæmentaria*, de Filippi, 1849.

*Hæmentaria officinalis*, de Fil.

Inhabit Mexico, where they are used for medicinal purposes.

Genus. *Placobdella*, R. Blanch.

*Placobdella catenigera*, Moq.-Tandon.

Indigenous to South Russia, Hungary, Italy and South France. It is a parasite of the swamp turtle, but frequently attacks human beings.

G. *ARTHROPODA* (Jointed-limbed Animals).

BY

FRED. V. THEOBALD, M.A.

BILATERALLY symmetrical segmented animals which are covered with a thick cuticle that is frequently calcareous (Crustacea), but always thinner between the segments; they carry (primitively) a pair of jointed appendages on every segment.[321] The segments of the body are uniform in certain regions, but differ from those of contiguous regions, so that it is easy to distinguish three parts (head, thorax and abdomen), each composed of segments. The cephalic segments are always formed into a uniform head, the segmentation being scarcely recognizable at either end; the thoracic segments may also fuse, or part or all of them may coalesce with the head; the abdomen, as a rule, retains its segmentation, but this may possibly also be lost, in which case it is [sometimes] united to the cephalothorax. The structure of the three regions depends mostly on the varying form and function of the appendages: those on the head are primitively locomotive organs (and frequently are still so in the early stages), but they become transformed into feelers and mouth-parts (mandibles, maxillæ); the limbs of the thorax, however, usually retain their ambulatory functions, as frequently do those of the abdomen; sometimes, however, the abdominal limbs disappear, entirely or partly; in the latter case they are then utilized for other purposes.

[321] [In most Arthropoda the skin is hardened by a deposit of chitin (Hexapoda, etc.).--F. V. T.]

In their organization the Arthropoda approach the segmented worms.

The Arthropoda are generally divided into five groups (Crustacea,[322] Protracheata, Arachnoidea, Myriapoda,[323] and Insecta or Hexapoda), of which only the Arachnoidea and the Hexapoda interest us here.

[322] Parasitic or free-living Crustaceans may now and then invade man abnormally. Thus, according to Betten, Caligus curtus invade the cornea (Betten, R. A., “Par. Crust. as a Foreign Body on the Cornea,” Lancet, 1900, i, p. 1002; and Centralbl. f. Bakt. u. Par., xxix, p. 506). According to Laboulbène, also Gammarus pulex (Laboulbène, A., “Obs. d’accid. caus. par le G. pul. apport. avec l’eau de boison dans l’estomac d’un homme,” Bull. Acad. méd., 1898, p. 21).

[323] R. Blanchard has compiled thirty-five cases in which Myriapoda have been observed in the intestine as well as in the nose of human beings (“Sur le pseudopar. d. myriap. chez l’homme,” Arch. de Par., 1898, i, p. 452). E. Munoz Ramos reports an additional case (ibid., p. 491). A few years ago a doctor in East Prussia sent me a rain worm out of a lady’s nose (cf. Hanau, A., “Wahrsch. Pseudo-paras. v. Schmeissfliegenlarv. u. angebl. Paras. v. Regenwürmern b. einer Hysterischen,” Arch. de Par., 1899, ii, p. 23).

A. *ARACHNOIDEA* (Spiders, Mites, etc.).

The head and thorax are always united together; the abdomen is either segmented or without exterior segmentation, in which case it is united with the cephalothorax.[324] The number of pairs of appendages amount to six, of which the two front pairs, the cheliceræ and the pedipalpi, are attached to the head region and the four remaining pairs to the thoracic region.[325] The abdomen in the adult condition has no appendages. The Arachnoids are air-breathers, and for this purpose are either provided with tracheæ or with so-called lung-sacs, or they breathe through the surface of the body. Some aquatic forms breathe by gills.

[324] [This is only so in the Acarina or mites, not in the Araneida or spiders.--F. V. T.]

[325] [The true character of the Arachnoidea is the presence of four pairs of ambulatory appendages. This number is reduced to two pairs in the gall-making Phytoptidæ, and they differ from all other Arthropoda in having no antennæ.--F. V. T.]

There are eight or ten orders of Arachnoids,[326] of which, however, only two, the Acarina and the Linguatulida, have to be considered here.[327]

[326] Twelve orders are now recognized, as follows: Pentastomida or Linguatulids; Tardigrada or bear-animalcules; Phalangidæ or harvest-men; Acarina or ticks and mites; Palpigradi; Solifugæ; Pseudoscorpionidea or book mites; Pedipalpi or false scorpions; Scorpionidea or true scorpions; Araneida or spiders; Xiphosura or king crabs; and Pycnogonida, marine Arachnoids.

[327] Chelifer cancroides has also been observed as a pseudoparasite in man (Arnault de Very, S., “Pseudopar. du. Chel. cancr. chez l’homme,” Compt. rend. Soc. de Biol., 1901, liii, p. 105).

Order. *Acarina* (Mites).

Small Arachnoids, the three parts of the body of which are, as a rule, coalesced; it is only rarely that a faint line indicates the division between a cephalothorax and abdomen. The two appendages on the head are designed for biting or puncturing and sucking, and vary according to their use. The cheliceræ[328] are fang-like jaws or puncturing bristles forming a kind of rostrum, the pedipalpi are claw-like or shear-shaped, or form a suctorial proboscis.[329] The four pairs of legs are usually well developed, more rarely they are rudimentary or have partly vanished; many parasitic forms are provided with pedunculated suckers [ambulacra--F. V. T.]. Respiratory organs (tracheal tufts) may be present or absent. The nervous system is reduced to a minimum, eyes are usually lacking. The intestine, situated in the central part, generally has three blind appendages; the anus is situated on the venter above the posterior end. Sexes separated; nearly all the species deposit eggs, from which six-legged larvæ hatch. The Acarina live either free in the water or in moist soil, or they are parasitic on plants and animals.[330]

[328] [The cheliceræ are sometimes regarded as modified antennæ, but it is more natural to regard them as the morphological equivalent of the mandibles of Hexapoda.--F. V. T.]

[329] [The pedipalpi, or second pair of jaws, consist of a stout basal segment and a palp, which may have the appearance of a leg in Arachnida; this may end with or without a claw, or with a chela (scorpions); they may also form a tube enclosing the styliform cheliceræ (mites).--F. V. T.]

[330] [Acarina are also found living upon trees, feeding upon other Arthropods and also upon spores of lichen and fungi (Oribatidæ or beetle mites); they also swarm indoors amongst stores and provisions (Tyroglyphidæ and Glyciphagi, household, sugar and cheese mites). This order is very important, as many are parasites upon man, his domestic animals and his cultivated plants, and attack his provisions and stores. Some live on blood, and in some of the ticks distribute various protozoal and other blood parasites and germs.--F. V. T.]

Family. *Trombidiidæ* (Running Mites).

Soft-skinned Acarina with tracheæ and with two eyes, usually pedunculated; they are often brightly coloured; cheliceræ lancet- or claw-shaped; pedipalpi claw-like; legs composed of six segments, with suctorial discs between the terminal ungues.[331] Larvæ six-legged. To the latter belong the larvæ of several species of Trombidium such as:--

[331] [Some have seven segments to the legs.--F. V. T.]

Genus. *Trombidium*, Latreille (and *Leptus*).

*Leptus autumnalis*, Shaw, 1790.

Leptus occur as parasites in the human skin and cause a cutaneous disease known as autumn erythema, and produce a very unpleasant sensation on account of the troublesome itching; in children it is very often accompanied by fever.[332]

[332] [This minute parasite is especially obnoxious in barley fields. In walking over barley stubble one is sure to be attacked by this Acarus in many districts. Trombidium is often very prevalent in gardens, especially along rows of peas, and in spring they may be found on fruit trees and bushes. Nut-pickers are frequently attacked by Leptus, and also pickers in other fruit plantations. It is often called the harvest mite.--F. V. T.]

Formerly these mites were considered adult forms, but when they were recognized as mite larvæ they were taken for those of the spider-mite (Tetranychus telarius); the investigations of Hanstein, however, showed this to be a mistake. When Henking first investigated the development of Trombidium fuliginosum, parasitic in the larval stage on vine-fretters, he demonstrated the occurrence of a form very similar to Leptus autumnalis, and the “autumn, grass, or gooseberry” louse was commonly designated the Trombidium larva. Even before Henking’s work it had been described by Mégnin as the larva of Trombidium holosericeum, a red-coloured species, frequently occurring in spring and summer on the ground, trees, etc. This assumption, however, as Moniez was the first to explain, is not correct; indeed, as many as three species come under consideration: T. gymnopterosum, L., T. fuliginosum, Herm. (according to Brucker), and two species known hitherto only in the early stage, T. striaticeps, Helm. et Oudem., and T. poriceps, Helm. et Oudem., which are not only parasitic on mammals, but on birds, on Arthropods and especially on insects. Arthropods appear to be the normal hosts for the larvæ.

The above-mentioned forms invade the skin of man by means of their oral apparatus, by preference invading the orifices of the sebaceous glands so as to suck the blood; around the point attacked there arises a wheal about the size of a lentil, and around the inserted hypopharynx a fibrinous secretion, the “proboscis,” which, however, is a product of the host, just as chitinous secretions are provoked by Trombidia parasitic on Arthropods.

Further species, analogous in habit to Leptus autumnalis, are described by Riley from Central and South America as L. americanus and L. irritans.

[L. autumnalis attacks small mammals by preference, such as moles and hares, which are often literally covered with them. Dogs are also subject to their attack, and cats suffer similarly. This mite also frequently appears in colonies on cows; cavalry horses after autumn manœuvres often suffer from an erythematous affection about the hocks and knees due to this pest.

[A number of Leptus, so far undescribed, occur abroad which attack man in the same way as L. autumnalis in Europe. Dr. Durham has brought me specimens from British Guiana called bête rouge; this species works under the skin much as does our European species, but it is very distinct, being considerably larger.--F. V. T.]

*Trombidium tlalsahuate*, Lemaire, 1867.

T. tlalsahuate occurs in Mexico under conditions similar to those of Leptus here. It also frequently attacks men, and especially fastens itself on to the eyelids, in the axillae, navel, or on the prepuce; it induces itching and swelling of the parts affected, and sometimes even causes suppuration; the symptoms, however, generally disappear after a week and remain localized.[333]

[333] Lemaire, “Import. en France du tlalsahuate,” Compt. rend. Acad. Sci., Paris, 1867, lxv, p. 215.

Other species of mites which attack man are reported, mostly by travellers, from various other places; zoologically, however, there is little known about them. The pou d’agouti in Guiana, niaibi in New Granada, colorada in Cuba, mouqui in Para, and the buschmucker in New Guinea represent a few of these.

*Akamushi* or *Kedani*.

In a few districts of Japan there occurs a serious illness, with a mortality of 40 to 70 per cent. It is called river or flood fever, and the Japanese doctors have connected it with a small mite (akamushi, kedani). Baelz has opposed this opinion on the grounds that he has repeatedly observed the same species of mite in his dwelling without any subsequent illness occurring. According to Keïsuke Tanaka, however, a connection certainly does exist, inasmuch as the akamushi, like Leptus, attacks persons to suck blood. If the mite is not removed, or if the spot attacked is injured by scratching, etc., a papule surrounded by a red area forms, and a pustule ensues; and finally a black scab covers the seat of injury. The lesion becomes the point of entrance of bacteria, especially a species of proteus which produces river fever. If the mites are carefully removed no general illness takes place.

The orange-red mites, which we only know in their larval condition, measure 0·16 to 0·38 mm. in length by 0·10 to 0·24 mm. in breadth. They have leg-like palpi with three joints, hirsute bodies, and very hairy legs composed of five segments, terminating with three ungues.

Family. *Tetranychidæ* (Spinning Mites).

These have tracheæ and eyes; the palpi are composed of four segments, of which the last but one has a powerful claw. The legs have six segments with sucker discs between the claws.

[The red spiders or spinning mites (Tetranychi) are usually placed in the family Trombidiidæ.--F. V. T.]

Genus. *Tetranychus*, Dufour.

*Tetranychus molestissimus*, Weyenbergh, 1886.[334]

[334] [This species is also known as Bicho colorado. It spins a web under the lower surface of the leaves, and it is only from December to February that it attacks warm-blooded animals and man.--F. V. T.]

Found in Argentine and Uruguay on the under surface of the leaves of Xanthium macrocarpum; it attacks mammals and men, producing severe itching, accompanied by fever in the latter.

It has been asserted by Haller that the CAPE AILMENT (Port Natal sickness) is caused by mites, but this statement has been contested.

*Tetranychus telarius*, L., 1758,[335] var. *russeolus*, Koch.

[335] [There is something wrong here, probably in the identification. T. telarius is purely a plant-feeder, and it is extremely unlikely a variety would attack man. Anyhow, it will not do so in Great Britain.--F. V. T.]

This common spinning mite likewise attacks human beings, but the papules produced by it very soon disappear.

Family. *Tarsonemidæ.*

A family distinguished by complete sexual dimorphism, the species of which are provided with tracheæ; the legs have five segments; the terminal segments of the front pair of legs of both sexes possess a claw; the terminal segment of the posterior pair of legs of the male likewise has a claw. In the female this pair of legs, like the second and third pairs of both sexes, is provided with two hooklets and a sucking disc. The cuticle of the body on the back is “annulated.”

[This family of small transparent mites live normally as plant parasites. The last two pairs of legs are widely separated from the two front pairs.--F. V. T.]

Genus. *Pediculoides.*

*Pediculoides ventricosus*, Newport, 1850.

Syn.: Heteropus ventricosus, Newport, 1850; Acarus tritici, Lagrèze-Fossot, 1851; Physogaster larvarum, Lichtenstein, 1868; Sphærogyna ventricosa, Laboulbène and Mégnin, 1885.

Males are oval in shape, 0·12 mm. in length and 0·08 mm. in breadth, flattened. There are six pairs of chitinous hairs on the dorsal surface and a lyre-shaped lamella on the posterior part. The female in the non-gravid state is cylindrical in form, 0·2 mm. in length and 0·07 mm. in breadth; when gravid the posterior part of the body becomes enlarged into a ball, which may attain 1·5 mm. in size, as in the case of Pulex penetrans and of the female Termites. On emerging the young are already provided with four pairs of legs and copulate soon after birth.

These animals live on the stalks of cereals, and feed on vegetable and animal juices; they are also found on corn-infesting insects. They invade the barns and seek out the insects living in the dry grains of corn, or wait for an opportunity of obtaining food. They have been repeatedly observed on human beings, particularly labourers occupied in handling grain; their bite causes severe irritation, local elevation and reddening of the epidermis, as well as fever. It cannot be positively asserted that all cases of the occurrence of cereal mites on man relate to P. ventricosus, as the descriptions are often insufficient. Geber states that one form is Chrithoptes monunguiculosus, or Acarus hordei; Flemming mentions Tarsonemus uncinatus; Koller Oribates sp.; and Karpelles Tarsonemus intectus.

[The pregnant female Pediculoides has a large round inflated abdomen, in which the ova hatch and the young mature. Later they escape from the parent as adults.--F. V. T.]

Genus. *Nephrophages.*

*Nephrophages sanguinarius*, Miyake and Scriba, 1893.

Males measure 0·117 mm. in length and 0·079 mm. in breadth; females up to 0·360 mm. in length by 0·120 mm. in breadth. The head is provided with two very large scissors-like jaws and two large round eyes. The legs are composed of five segments and are all of equal length; the three anterior pairs of legs have pedunculated ambulacra, the posterior ones terminate in a claw. The cuticle on the back is thickened in three places, shield-like; the abdominal surface without scutellum is longitudinally striped and is beset with chitinous hairs. Colour greenish to brownish-yellow. Eggs 0·046 to 0·040 mm.

The authors discovered these mites, but always dead, in the urine of a Japanese suffering from fibrinuria complicated with chyluria and hæmaturia. They surmised that they were endoparasites, probably situated in the kidney; but this view is not convincing, though they also report that for a week, day after day, the mites were found in the patient’s urine, as well as in urine drawn off by means of a catheter, and in the water used to wash out the bladder (one or two specimens and an egg). The statement that these mites have large eyes makes the discovery suspicious, to say the least. The significance of the discovery is not supported by the further statement that Disse is supposed to have found an encapsuled mite closely related to the Tyroglyphides on the wall of the vena cava.

In the case of Marpmann, who found a dead Acarid in the urine of a man suffering from chronic nephritis, and in whom later examinations proved negative, the author himself was of opinion that the mite had reached the urine from outside.

We are certainly acquainted with mites living endoparasitically, namely, the Cysticolæ, Analgesinæ, of which Laminosioptes gallinarum live in the intramuscular and subcutaneous connective tissue of fowls, and Cytoleichus sarcoptoïdes in their air sacs. Another kind of mite (Halarachne halichœri) is occasionally found in the nasal mucous membrane of the seal (Halichœrus grypus), and, quite recently, Pneumonyssus simicola, which is more nearly related to Halarachne, has been found in the lung of Cynocephalus sp. It is therefore not improbable that endoparasitic mites are found in man; but no definite discovery has yet been made.

Family. *Eupodidæ.*

Small tracheate mites, with moderately long or short pedipalpi, composed of four segments, of which the last segments bend; cheliceræ forceps-shaped, with serrated edges; legs with two claws, more rarely with one, and terminating in a tuft ornamented with fine hairs; genital orifices on the abdomen, surrounded by a circle of little hairs. Most species live free--one lives parasitically on the bodies of slugs.

Genus. *Tydeus*, Koch.

*Tydeus molestus*, Moniez, 1889.

Male, 0·2 mm. in length, 0·125 mm. in breadth. Females, 0·225 mm. in length, 0·135 mm. in breadth; gravid female 0·315 to 0·360 mm. in length and 0·180 mm. in breadth. They were observed by Moniez on an estate in Belgium, whither the creature had apparently been imported twenty-five years previously with Peruvian guano; they appeared regularly in the summer and remained until the first frost set in; they were found on grass-plots, on trees and bushes in masses; they regularly attacked human beings, mammals and birds, tormenting their hosts in a terrible manner.

Family. *Gamasidæ* (Coleopterous or Insect Mites).

Cheliceræ chelate or styliform; pedipalpi filiform; the legs are composed of six segments with two terminal ungues and a bladder-like sucking disc [caruncle--F. V. T.]. Stigmata situated between the third and fourth pairs of legs; the cuticle thickened, leather-like; no eyes; the larvæ have six legs.

The Gamasidæ are predaceous on small insects and other mites; some are parasitic on insects, and one is noticeable as a pest on birds, etc.

Genus. *Dermanyssus*, Dugés.

*Dermanyssus gallinæ*, de Geer, 1778.

Syn.: Pulex gallinæ, Redi, 1674; Atarus gallinæ, de Geer, 1778; Dermanyssus avium, Dugés, 1834.

The male measures 0·6 mm. in length by 0·32 mm. in breadth; the female 0·7 to 0·75 mm. in length by 0·4 mm. in breadth. The body is somewhat pear-shaped; the colour whitish, reddish, or reddish-black, according to the contents of the intestine. The legs are fairly short and strong. During the day they live concealed in the nests, cracks, etc., of the hen-house, and at night attack the inmates in order to suck their blood; they rarely remain long on the birds. They have been repeatedly found on persons, on whose skin they produce an itching eruption.

*Dermanyssus hirundinis*, Hermann, 1804.

Syn.: Acarus hirundinis, Herm., 1804.

Of a brownish colour, 1·2 or 1·4 mm. in length; lives in the nests of swallows and is occasionally found on man.

[The red hen mite (Dermanyssus gallinæ) not only attacks poultry and man, as stated above, but is found on all birds and many mammals. The D. gallinæ is the same as D. avium. The species found in swallows’ nests is also said to be the same. This mite can remain for weeks without any food from its normal host. They only attack man when entering or cleaning dirty and neglected fowl-houses; they do not produce a true dermatosis. They chiefly attack the backs of the hands and forearms of those who constantly attend poultry and give rise to symptoms similar to the papular eczema of scabies. That they may remain some time upon the human body we know from the following cases out of many recorded: Geber observed that the Dermanyssus had caused a diffused eczema on a woman, which lasted four weeks and then disappeared. The tique of F. V. Raspail is the bird Dermanyssus; he records children and adults being attacked not only when handling pigeons, but even when walking in a garden manured with pigeons’ dung. The affection soon disappeared when the pigeons were destroyed and the excreta buried. I have frequently heard of poultrymen being seriously attacked by this pest.--F. V. T.]

Genus. *Holothyrus.*

*Holothyrus coccinella*, Gervais, 1842.

Measures 5 mm. in size; lives on birds in the Island of Mauritius; ducks and geese frequently fall victims to its bite; it also attacks human beings, on whose skin it causes severe burning and swelling, but no reddening; it may be dangerous to children, especially by settling in the oral cavity.

Other Gamasides occasionally occur in man, for instance, according to Moniez, Leignathus sylviarum, Canestr. et Fanzago; according to Neumann Lælaps stabularis. The former live normally in the nests of various species of Sylvia, Lælaps on dried vegetable substances, also in houses.

[Marchoux and Conoy (Bull. Soc. Path. exot., 1912, v, No. 10, pp. 796–798) found Leishman granules in Lælaps echidninus. It is assumed that Leishman granules may be found in most Arachnoids, and have no connection with Spirochæta.--F. V. T.]

Family. *Ixodidæ* (Ticks).

Comparatively large Acarines with a leathery skin; they are flattened in form, but after sucking blood the abdomen becomes spherical; the cheliceræ are rod-like and possess a serrated terminal joint, bent hook-like; the median parts of the pedipalpi (maxillæ) form a rostrum furnished with barbed hooks (fig. 359); the maxillary palpi themselves are club-like or rounded; the legs are composed of six segments with two terminal ungues, often also with “sucking discs”; the stigmata are at the sides of the body, posterior to the fourth or third pair of legs. The larvæ are six-legged.

[The true ticks (Ixodidæ) are all blood-suckers, and as far as is known they do not take vegetable food at all. Not only are the Ixodidæ important as actual parasites, but they are most so on account of the fact that they are the active agents in carrying various diseases in animals and apparently in man. It has been conclusively proved that the bont tick (Amblyomma hebræum) is the carrier of the fatal “heart-water fever” so rife amongst sheep in South Africa, that the dog tick (Hæmaphysalis leachi) is the agent by which the protozoa that cause malignant jaundice in dogs are distributed, that Texas fever in cattle is spread by Rhipicephalus annulatus, and Coast or Rhodesian fever by R. appendiculatus and R. simus. Their importance as disease carriers amongst mammals is therefore considerable, and it may prove to be so for man.[336] They frequently attack man, but chiefly, according to my observations, in their early stages in Europe; this is not so, however, abroad. The life-history of a number of ticks has been clearly demonstrated. Mr. Wheler has shown that in Ixodes reduvius it is as follows: the female deposits her eggs in masses upon the ground, gradually reducing in size as the eggs pass out, until she finally remains a mere shrivelled empty bag and then dies. The eggs are oval, golden brown in colour and smooth; in length they are 0·59 mm.; as in all Ixodidæ they are covered with a glutinous secretion, by means of which they adhere together in masses. These egg masses may be deposited anywhere on the ground, but amongst rough, coarse herbage seems to be the favourite place. The egg stage may last as long as twenty-two weeks, or it may only take eight weeks. In the case of the bont tick a single female may deposit 15,000 or more eggs. The process of egg-laying is described as follows by Mr. Wheler: “When egg-laying is about to take place, the head is further depressed till it rests close against the under side of the body. In this attitude the end of the rostrum actually touches the genital orifice, the palpi being at the same time widely opened out. Behind the head and from beneath the shield, at what for the purposes of explanation may be described as the back of the neck, a white, perfectly transparent, delicate gelatinous membrane is brought down through inflation, either with air or with a transparent fluid, above the head, which it temporarily conceals. The end of this membrane terminates in two conical points which appear to be covered with a glutinous secretion, and at the same time an ovipositor of a somewhat similar character, but only semi-transparent, is pushed forward from the genital orifice. This latter is a tube, within which is the egg. As the ovipositor projects it turns itself inside out, like the finger of a glove, leaving the egg protruded at the end and lying between the two finger-like points of the membrane. The membrane and the ovipositor are then withdrawn each from the other. The egg adheres to the former, which collapses through the withdrawal of its contents, dragging the head forward and depositing it on the top of the head. Neither legs, palpi, nor the organs of the mouth take any part in oviposition, but after the collapse of the membrane the palpi are closed and the head is raised, by which action the egg is pushed forward to the front edge of the shield, forming in time an adherent mass of eggs, which are deposited in front of the tick.”

[336] This has been proved in Uganda--so-called tick fever in man.

[The egg gives rise to the larval form, the so-called “seed-tick” stage. At first these minute specks are pallid and soft, but they soon harden and darken in colour. These larvæ are six-legged and crawl up grasses and various plants, and there await a passing host, waving their two front legs in the air and becoming attached by this means. The larval ticks feed upon the blood of the host, and when replete fall to the ground, the body becoming inflated in the meanwhile. These larvæ may remain on the host only two days, or they may remain much longer. Eventually they moult on the ground and change to the nymph or pupal stage, which has four pairs of legs. This pupa acts just as the larva, crawls up plants and waits to regain the host. After a time the nymphs, having gorged themselves with blood, fall off and remain on the ground for nearly three months; they then moult and become adult males and females. In about ten days they assume their normal colour and regain the host afresh; the female gradually swells until she attains that large inflated form so characteristic of ticks. The male does not swell, but nevertheless feeds upon the host and fertilizes the female.

[The act of coitus is strange: the male tick inserts its rostrum and other mouth organs into the sexual orifice of the female, between the base of the posterior pair of legs. The males then die and the females fall to the ground and deposit the ova. There are variations in the different species, of course, from those given above, which apply solely to Ixodes reduvius. The larvæ and nymphs seem to attack most animals, but the adults mainly keep to the same host. The periods in the life-cycle of ticks not only vary in the different species, but in each species according to climatic conditions; for instance, in the bont tick (Amblyomma hebræum, Koch), Lounsbury has shown that the development is rapid in summer, slow in winter. The period from the time that the female drops to the time she commences to lay eggs varied in specimens observed by him from twelve days in summer to twelve weeks in winter, and the complete period from the dropping of the female to the hatching of the eggs, from eleven weeks in summer to thirty-six weeks through the winter. Other stages vary in a similar manner.

[Ticks may live a long time away from the host provided they are supplied with a certain amount of moisture. Mr. Wheler kept dog ticks (Ixodes plumbeus) in the larval stage for ten months; the pupæ, male and female, of I. reduvius for six months.

[I have kept Ornithodorus moubata alive for eighteen months without food.

[In many species moulting takes place off the host, but in I. bovis, now known as Rhipicephalus annulatus, Say (the carrier of Texas fever), moulting takes place on the host, and in many other species also.[337] Some species of ticks leave their host on its death (as the dog tick, Hæmaphysalis leachi), but others die with the host (bont tick, Amblyomma hebræum).

[337] Some ticks require only one (R. decoloratus), others two (R. evertsi), and some three hosts (R. appendiculatus) in order to reach maturity.

[Two species are of special importance, namely Ornithodorus moubata, Murray, which may infect human beings with the spirillum of African tick fever, and Dermatocentor reticulatus var. occidentalis, which is said to be the carrier of Rocky Mountain spotted fever.

CLASSIFICATION OF Ixodidæ.

[The ticks, or Ixodidæ, are divided into two groups, known as (1) Argantinæ, (2) Ixodinæ. The Argantinæ are told from the Ixodinæ by the absence of dorsal or ventral shields in both sexes, and also by the rostrum being placed beneath the cephalothorax, which covers it over: except in the larval stage, in which it is subterminal, and in the pupal, when it partly projects. Legs nearly equal in length. The sexual orifice is situated between the two first pairs of legs. The males usually smaller than the females.

[The Ixodinæ have the legs unequal, of six segments with two false segments, making them look as if composed of eight segments. The rostrum is terminal and never hidden beneath the body. The sexual orifice is situated between the bases of the first three pairs of legs. In the males the orifice is obsolete or very rudimentary, sexual intercourse being effected by the rostrum. The males are smaller than the females. The shield in the females never covers so much as one-half of the body even when fasting, also in the larvæ and nymphs; but in the males, which do not distend, the shield covers the body entirely, or all but a narrow margin. The Ixodinæ are divided into two groups: (i) the Ixodæ, and (ii) the Rhipicephalæ. The former have a long proboscis reaching nearly to the end of the palpi or even a little longer than the palpi. The palpi are longer than broad. The Rhipicephalæ have short palpi, nearly or quite as broad as long, more or less conical or subtriangular. They were called Conipalpi by Canestrini.

SYNOPSIS OF GENERA.

[A. Argantinæ: Rostrum concealed in adult, partly exposed in larvæ and nymphs. No dorsal and ventral shields. Body flat with thin edges, finely shagreened and punctate Argas. Body with numerous small round granules and with thick sides Ornithodorus.

[B. Ixodinæ: Rostrum terminal. Body with dorsal shield over some part of it.

I. Rostrum and palpi longer than broad (Ixodæ). α. A groove around anus in front. Palpi caniculated in both sexes Ixodes. Palpi claviform, not caniculated in the male; legs very long Eschatocephalus. Palpi claviform, not caniculated in the male; anal groove absent in the female Ceratixodes. β. A groove around the anus behind. No eyes; adanal shields Aponomma. Eyes present. Males with no adanal shields Amblyomma. Males with adanal shields Hyalomma. II. Labium and palpi short; palpi not, or very little, longer than broad (Rhipicephalæ). α. No eyes. Rostrum rectangular; no ventral shields in the male Hæmaphysalis. β. Eyes present. No adanal shields, but usually with greatly developed coxæ on fourth pair of legs. Capitulum quadrangular Dermacentor. Capitulum hexagonal Rhipicentor. Adanal shields in male. Stigmata comma- shaped Rhipicephalus. Stigmata oval or round; legs normal Boophilus. Segments of legs expanded Margaropus.

[The genus Ceratixodes of Neumann, 1902, occurs on birds. [The genus Eschatocephalus of Frauenfeld, 1853, of which seven species are known, is mostly parasitic on bats, and is found in holes, caves, and church towers. [The genus Aponomma of Neumann, 1899, is exotic, and almost entirely confined to snakes and saurians. [The following are synonyms of the different genera:-- Argas, Latreille, 1796 (Rhynchoprion, Hermann, 1804). Ixodes, Latreille, 1795 (Acarus, Linnæus, 1758; Cynorhæstes, Hermann, 1804; Crotonus, Dumeril, 1822). Ceratixodes, Neumann, 1902 (Ixodes, Cambridge, 1879; Hyalomma, Cambridge, 1879). Eschatocephalus, Frauenfeld, 1853 (Sarconyssus, Kolenati, 1857). Amblyomma, Koch, 1844 (Ixodes, Latreille, 1795). Hæmaphysalis, Koch, 1844 (Rhipistoma, Koch, 1844; Gonixodes, Dugès, 1888; Opitodon, Canestrini, 1897). Rhipicephalus, Koch, 1844 (Acarus, Linnæus, 1758; Ixodes, Latreille, 1795; Phanloixodes, Berlese, 1889; Boophilus, Curtice, 1890). Dermacentor, Koch, 1844 (Ixodes, Latreille, 1795; Pseudixodes, Haller, 1882).--F. V. T.]

Genus. *Ixodes*, Latreille.

*Ixodes reduvius*, L., 1758.[338]

[338] Ixodes reduvius and I. ricinus are synonymous. [The above should read Ixodes ricinus, Latreille, 1806.--F. V. T.]

Syn.: Acarus reduvius and ricinus, L.; Ixodes ricinus, Latreille, 1806.

The males are oval; their length 1·2 to 2 mm.; they are brownish-red or black in colour; the females are yellowish-red, 4 mm. long; when gorged they are lead-coloured, and may attain 12 mm. in length by 6 to 7 mm. in breadth.

The dog tick (fig. 360) lives in thickets on leaves, etc., and attacks sheep and oxen, and more rarely dogs, horses, and human beings, into the skin of which the female bores with the rostrum in order to suck blood; the bite is not dangerous, and sometimes is not even felt. Inflammation, however, is set up if the creatures are forcibly removed from the wound, as the rostrum as a rule is torn off in the process. If left alone or smeared over with some grease--vaseline, oil, butter, etc.--the creatures drop off spontaneously. Sometimes the entire tick bores itself into the skin; they also appear to be permanent inmates of kennels.

[The species I. reduvius is the same as I. ricinus, Latreille. The male is 2·35 to 2·80 mm. long; the body is dark brown, almost black, with a pale, almost white, margin; there are also traces of reddish mottling. Coxæ of the first pair of legs with a short spine. Rostrum much shorter than that of the female; shield oval; anal shield small, about one-third the length of ventral shield. The adult female varies from 2·80 to 3·5 mm. when not distended, but when gorged may reach 10 mm. long. The shield and legs are dark blackish-brown, body deep orange-red with four dark longitudinal lines, paler beneath and light grey in front. When distending it is pale red to grey or white; when fully gorged olive-green, or dark red to black, with irregular yellow streaks on the back and sides just before egg-laying. Sexual orifice opposite fourth pair of legs. The nymph varies from 1·60 to 1·70 mm. long when fasting; the body is olive-white, opaque, with four distinct brown posterior markings and similar anterior ones, leaving a pale centre to the shield. When fully gorged it is 3 mm. long. As the nymph distends, it changes from opaque white to blue-black, and finally black. The little larva is 0·80 to 1·50 mm. long, transparent with olive-green intestinal markings; as it becomes inflated it changes to blue-black, and then black. There are no eyes. It is widely distributed, and chiefly attacks sheep; sometimes it occurs on dogs and also attacks man. Mégnin records it from horses in the nymph stage. Amongst its other numerous hosts are goats, cattle, deer, hedgehogs, moles, bats, birds, and lizards. It is usually known as the grass tick and bottle-nosed tick. This species occurs in Europe, Asia, North Africa, and North America.

[Synonyms.--Considerable confusion exists over the name of this and other common ticks, owing to the same species having been described under a great many names. Observers have taken the same species on different animals and in various stages to be distinct, and have described them accordingly.

[The name Ixodes reduvius, Leach, does not stand, as Leach was describing quite a different parasite. The name I. ricinus, Latreille, 1806, is now substituted by Neumann and Wheler.

[The synonyms given by Wheler are as follow: Reduvius, Charleton, 1668; Ricinus caninus, Ray, 1710; Acarus ricinoides, de Geer, 1778; Acarus ricinus, Linnæus, 1788; Cynorhæstes reduvius, Hermann, 1804; Cynorhæstes ricinus, Hermann, 1804; Ixodes megathyreus, Leach, 1815; Ixodes bipunctatus, Risso, 1826; Cynorhæstes hermanni, Risso, 1826; Crotonus ricinus, Dumeril, 1829; Ixodes trabeatus, Audouin, 1832; Ixodes plumbeus, Dugés, 1834; Ixodes reduvius, Hahn, 1834; Ixodes fuscus, Koch, 1835 (?); Ixodes lacertæ, Koch, 1835 (?); Ixodes pustularum, Lucas, 1866; Ixodes fodiens, Murray, 1877; Ixodes rufus, Ixodes sulcatus, and Ixodes sciuri, Koch.--F. V. T.]

*Ixodes holocyclus*, Neumann, 1899.

[Under the name I. holocyclus, Cleland (Journ. Trop. Med. and Hyg., 1913, xvi, No. 3, pp. 43–45) says that: “This tick is common in man where there is dense scrub and tropical jungle along the east coast of Australia at certain times of the year. It may cause severe symptoms in children resulting in death.” He records a child being attacked in 1884 which died, and another case from which 200 ticks were removed, the symptoms being weak heart, collapse, syncope, but the patient recovered under treatment; again, in the same journal (pp. 188, 189), the case of a 4-1/2-year-old girl who was bitten showed widespread muscular paralysis, and other cases resembling conium poison.

[Taylor (Rep. Ent. Aust. Inst. Trop. Med., 1911, p. 21, 1913) refers to this species as the scrub tick of New South Wales. The partially fed female has a dark reddish-yellow scutum and is almost as broad as long, punctations very numerous, equal and confluent in places, long white hairs on the lower half of each coxa. He records it as attacking man commonly, mentioning Kamerunga, Cairns district, Queensland, and Sydney, N.S.W., as localities.--F. V. T.]

*Ixodes hexagonus*, Leach, 1815.

Syn.: Ixodes sexpunctatus, Koch, 1897; I. vulpis, Pagenstecher, 1861.

Lives in the same manner as the foregoing; especially attacks hounds, but also other mammals and even birds. The difference consists in the shape of the legs, the shorter rostrum, and the larger size of the male. It also occasionally attacks man, but is usually confused with the previously mentioned species.

[The synonyms of this species are as follow:[339] Ixodes autumnalis, Leach, 1815; I. erinacei, Audouin, 1832; I. reduvius, Audouin, 1832; I. crenulatus, Koch; I. erinaceus, Murray, 1877; _I. ricinus_, Mégnin, 1880.[339] Two other synonyms are given above by Braun.

[339] Neumann, G. L., “Rev. de la fam. des Ixodides,” III Mém. Soc. Zool. France, 1899, xii, p. 129.

[The female when fully replete is 11 mm. long, when fasting 3·86 mm.; the shield is heart-shaped and punctate, body finely hairy; palpi short and broad; labium shorter, and tarsi of all the legs more truncate than in I. ricinus. The colour of the distended body is drab and somewhat waxy; rostrum, shield and legs light testaceous. The male varies from 3·5 to 4·0 mm. long, and is reddish-brown in colour with lighter legs; the shield is punctate and leaves a narrow margin around the body; the body is elliptical, almost as large in front as behind. There is a spine on the coxæ of the first pair of legs, which is shorter than in the male I. ricinus and longer than in the female. The genital orifice is opposite the interval between the second and third pair of legs. The fasting nymph is 1·76 mm. long, light bluish-grey, margined and transparent, with four large posterior intestinal marks joined together behind the shield and smaller ones extending to the front and sides. When fully distended it is uniformly brownish-white; shield, legs and rostrum pale testaceous. The larva varies from 0·88 mm. when fasting to 1·76 mm. when gorged. Its body is light, but gradually becomes darker, with similar intestinal marks to ricinus.

[This tick is very common, especially on ferrets, stoats and hedgehogs. It is also found on sheep, cattle, etc. The males do not generally occur in company with the females on the host. Pairing probably takes place on the ground.--F. V. T.]

Genus. *Amblyomma*, Koch.

*Amblyomma cayennense*, Koch, 1844.

Syn.: Amblyomma mixtum, Koch, 1844; Ixodes herreræ, Dugés, 1887; Amblyomma sculptum, Berlese, 1888.

Characterized by the possession of eyes. The male measures 3·8 mm. in length by 3 mm. in breadth; the female 4 mm. in length by 3 mm. in breadth, but when full of blood may become 13 mm. in length and 11 mm. in breadth. They are common in the whole of Central America (Carrapatas), and attack mammals, amphibious animals and man.[340]

[340] Neumann, G. L., loc. cit., p. 205.

[This species was described by Fabricius. It occurs in Cayenne, Guiana, in Southern Texas, Florida, California, Mexico, Guatemala, Honduras, Nicaragua, Costa Rica, Panama, Bermuda, Cuba, Jamaica, Trinidad, Colombia, Venezuela, French Guiana, Brazil, Paraguay and the Argentine. It is called the silver tick. It frequently attacks man. Schwarz and Bishopp (Bull. 105, U.S. Dept. Agric., p. 158) heard of one man whose legs were well covered with suppurating sores and who was ill from the attack of these ticks and the wounds produced by scratching, and records other cases of their swarming on man. Newstead (Ann. Trop. Med. and Par., 1909, iii, No. 4, p. 442) records it as the worst pest to man in Jamaica.--F. V. T.J

*Amblyomma americana*, Linnæus.

The so-called long star tick, from the silvery spot on the apex of the scutum of the female. It will attack any mammal and even birds and also man. It occurs in North America, and also in Brazil, Guiana and Guatemala. Its punctures frequently end in suppuration. In the Eastern and Southern States man is more frequently attacked by this species than any other. Moss-gatherers in Louisiana are badly attacked by it.[341] It also attacks the milkers in dairies. Attempts to transmit Texas fever failed with this species.

[341] Morgan, “Ticks and Texas Fever,” Louisiana State Bull. 55, pp. 134, 135, pl. 59.

*Amblyomma maculatum*, Koch.

The so-called Gulf Coast tick, of the Gulf Coast, occurs on birds, mammals and man, especially cattle, and attacks the ears.

Genus. *Hyalomma*, Koch.

*Hyalomma ægyptium*, L., 1758.

Syn.: Acarus ægyptius, L., 1758; Ixodes camelinus, Fischer, 1823.

A species frequently found in Africa, particularly in Egypt and Algeria, and which also occurs in France and Italy, as well as in Asia. Male 8 mm. in length, 4·5 mm. in breadth. Female up to 24 mm. in length and 15 mm. in breadth. It infests large and small animals as well as human beings.[342]

[342] Neumann, G. L., loc. cit., p. 285; Ronsisvalle, “Sui fenomeni morb. prodotti nel uomo da un Ixodide denominato Hyal. æg.,” Boll. Acc. Gioenia sci. nat., 1891, xvii.

[This is one of the largest ticks, nearly reaching the size of the bont tick. It is known in Africa as the bont leg-tick; all farm stock is attacked, but sheep and goats suffer most. Only one generation appears to occur each year. The male is almost black with a pale marginal stripe; the replete female brown with irregular light blue stripes. It is abundant in parts of South Africa.]

Genus. *Hæmaphysalis*, Koch.

*Hæmaphysalis punctata*, Canestrini and Fanzago, 1877–1878.

Syn.: Hæmaphysalis sulcata, Canestrini and Fanzago, 1877–1878; Rhicocephalus expositicius, Koch, 1877; Hæmaphysalis peregrinus, Cambridge, 1889; Herpetobia sulcata, Canestrini, 1890.

[This species does not appear to be common. It occurs on sheep, goats, horses and cattle. I have seen a female taken from man in Britain. The female when fasting is 3·44 mm. long, when gorged 12 mm. long. Colour, reddish-brown, leaden-grey when gorged; dorsal shield deeply indented in front; rostrum, shield and legs brownish; body finely punctate, both above and below; sexual opening opposite the coxæ of the second pair of legs in both sexes. Palpi a little longer than the labium; first segment short and narrow, second and third widened on the dorsal face. Coxæ with a short, broad blunt spine; tarsi short, terminated with a spur on the first pair. The male is 3·10 mm. long. Body rather narrow, yellowish to reddish-brown; dorsal shield nearly covers the whole body; numerous punctures over the whole surface. Eleven indentations on the posterior margin of the body; peritremes lighter in colour, large and comma-shaped. The three anterior pairs of legs with a short spine on the haunches, the fourth with a very long one directed backwards. The nymph varies from 2·5 to 3·0 mm., is oval, and light yellow to dark red in colour. Dorsal shield rounded with few punctations. No spur on tarsi, and sexual orifice nearly obsolete. Larva short and oval. Length 1·20 mm.--F. V. T.]

Genus. *Dermacentor*, Koch.

*Dermacentor reticulatus*, Fabricius, 1794.

Syn.: Acarus reticulatus, Fabr., 1794; Ixodes reticulatus, Latreille, 1806; I. marmoratus, Risso, 1826.

This tick is provided with eyes, but it is distinguished from Ixodes and analogous genera by the lack of the abdominal plastron in the male, which measures 5 to 6 mm. in length by 3·5 mm. in breadth. The female may attain 16 mm. in length and 10 mm. in breadth. It is found in the South of Europe, in Asia, and in America; it attacks chiefly oxen, sheep and goats, and occasionally man.[343]

[343] Neumann, G. L., “Rev. de la fam. des Ixodides,” Mém. Soc. Zool. France, 1897, x, p. 360.

[This tick sometimes causes much annoyance to human beings. It was once most troublesome at Revelstoke. Specimens have recently been found on fowls, turkeys and pheasants in Kent.

[Other synonyms are as follows: Cynorhæstes pictus, Hermann, 1804; Crotonus variegatus, Dumeril, 1829; I. pictus, Gervais, 1844; Dermacentor albicollis, Koch, 1844–1847; D. pardalinus, Koch, 1844–1847; D. ferrugineus, Koch, 1844–1847; Ixodes holsatus, Kolenati, 1857; Pseudixodes-holsatus, Haller, 1882; Hæmaphysalis marmorata, Berlese, 1887.

[The female when fasting is 3·86 mm. long by 2 mm. wide. The body is depressed, larger behind and reddish-brown in colour. The shield is very large and extends to the level of the third pair of legs, with a few large and many small punctations, milky white, variegated with reddish-brown. Sexual orifice opposite the coxæ of the second pair of legs. Coxæ of the front legs are deeply bifid, the others with a moderate spine. When gorged light brown, and may reach 16 mm. When depositing eggs the female is mottled with dark brown above and below. The male is like the female. The shield is reddish-brown, variegated with a milky white pattern. Coxæ of the fourth pair of legs three times the size of the third. There is a sharp backwardly pointing spine on the second palpal segment, also seen (but smaller) in the female. Length 4·20 mm.

[According to Mr. Wheler this is a very variable species both in size and colour. It occurs in England on sheep, but not commonly. It has probably been introduced into Britain. Besides the animals mentioned above it is also found on deer.--F. V. T.]

*Dermacentor venustus*, Banks.

[The Rocky Mountain tick fever tick. This species has been wrongly called Dermatocentor reticulatus var. occidentalis. The correct name of the carrier of Rocky Mountain tick fever is Dermacentor venustus, Banks (Hooker, Bishopp and Wood, Bull. 106, U.S. Dept. Agric., Div. Ent., p. 165).

[The female is from 13·8 by 10 by 6·4 mm. to 16·5 by 11·4 by 6·9 mm. when gorged; the male from 2·1 by 1·5 mm. to 6 by 3·7 by 1·4 mm. The male reddish-brown; scutum with an extensive pattern of white lines, usually but little white on the mid-posterior region, legs slightly lighter than scutum, joints tipped with white. Female with scutum mostly covered with white, abdomen reddish-brown, legs as in male. The nymph when unengorged reddish-brown, when gorged dark bluish-grey; the larva is yellowish-brown when unengorged, slate blue when engorged. The ova light brown, shiny and smooth.

[The chief wild hosts are the brown bear, coyote, woodchuck, rabbit, wild cat, badger and mountain goat for the larvæ; practically all small mammals act as hosts for larvæ and nymphæ, whilst the adults are seldom found on other than large domestic animals; horses and cattle are preferred. It occurs in British Columbia, southward to Northern New Mexico, and from the foothills of the Rocky Mountains in Colorado to the base of the Cascade Range in Oregon and California; abundant in Western Montana, Idaho, Eastern Washington, Oregon, North Utah, West Wyoming and North-west Colorado.

[Of great importance in the Bitter Root Valley of Montana, where a number of cases of fever occur each year, with a mortality of about 70 per cent. In British Columbia this tick causes tick paralysis in man and sheep. Only the adults seem to attack man and animals there (Hadwen and Nuttall, Parasitology, 1913, vi, No. 3, pp. 288–297 and 298–301) according to the Canadian Medical Association Journal, December, 1912. The symptoms are unlike spotted fever. For full details of this tick vide Bulls. 105 and 106, U.S. Dept. Agric.]

*Dermacentor occidentalis*, Neumann.

This tick only occurs in the Pacific Coast region of the United States. Owing to the fact that it frequently attacks man as well as occurring in great abundance in Oregon and California, it is of considerable economic importance. It is spoken of as the wood tick, and in the regions where found is the most common tick to attack man. Hooker, Bishopp and Wood (Bull. 106, U.S. Dept. Agric., Div. Ent., 1912, p. 189) state that a number of cases have been brought to their notice where the bite of this tick has caused considerable local inflammation, which in some cases required physicians’ attention. It has been supposed to be connected with Rocky Mountain spotted fever, but it is doubtful if it is concerned in its transmission. The engorged female is steel grey, the dorsum with an olive-green surface colour, which covers the grey except in small spots, giving a mottled appearance. The unengorged males and females are reddish-brown, scutum covered with a whitish bloom, interrupted by many red punctures. The female is 9 by 6·1 by 3·3 mm. to 11·8 by 7·6 by 5·6 mm.; the male 2·8 by 1·6 mm. to 4·2 by 2·3 mm. The larvæ are bluish-grey when engorged, reddish-brown when unengorged. The nymph is light brown, sides of scutum darker, and the intestines dark brown. It is confined to the Coast Range and Sierra Nevada Mountains in California and Oregon and the small mountain range to the south-west.

*Dermacentor variabilis*, Say.

The American dog tick has also been found on man, but it is of little economic importance as it is easily removed from its host.

Genus. *Margaropus*, Karsch.

*Margaropus annulatus australis*, Fuller.

The so-called Australian cattle tick. Newstead[344] reports this as a great pest to man in Jamaica in its larval stage. Its chief hosts are cattle, horses, goats, sheep, dogs and rabbits.

[344] Ann. Trop. Med. and Par., 1909, iii, No. 4.

*Margaropus microplus*, Canestrini.

Recorded by Aragão (Mem. Inst. Oswaldo Cruz, 1911, iii, fasc. 2, p. 163) as occurring in larval stage on man in Brazil.

Genus. *Rhipicephalus*, Koch.

*Rhipicephalus sanguineus*, Latreille, 1804.

Syn.: Ixodes sanguineus, Latr., 1804; I. rufus, Koch, 1844; Rhipicephalus limbatus, Koch, 1844; Rh. siculus, Koch, 1844; Rh. stigmaticus, Gerstäcker, 1873.

Spread over almost the entire tropical and sub-tropical regions, occurring in Europe in the South of France and in Italy; it infests dogs and more rarely sheep; oxen, cats, foxes and human beings are also attacked.[345]

[345] Neumann, G. L., loc. cit., 1897, p. 385.

NEUMANN’S TABLE OF SPECIES OF ARGAS.

1 {Body elliptical (sides curved) 2. {Body oblong (sides straight), ending anteriorly { in a point 7. 2 {Body transversely oval vespertilionis. {Body elongate oval 3. 3 {Margin of body striated 4. {Margin of body formed by quadrangular areolæ PERSICUS. 4 {Body flat, integument plainly wrinkled 5. {Body tumid, elongate; integument finely { wrinkled; coxæ of fourth pair of legs near { anterior third of body hermanii. 5 {Body oval, narrowed anteriorly REFLEXUS. {Body elliptical, blunt, hardly narrowed { anteriorly 6. 6 {Body twice as long as broad cucumerinus. {Body hardly longer than broad transgariepinus. 7 {Dorsal integument with large polygonal { depressions; tarsi appearing bifid BRUMPTII. {Dorsal integument almost smooth; tarsi not { appearing bifid æqualis.

The Argantinæ are distinguished from the Ixodinæ by the head, which in the former is situated on the inferior aspect of the cephalothorax, while in the Ixodinæ it projects freely; also by the very short proboscis, the small club-like palpi, the lack of suckers on the legs, as well as by the scutellum, which covers the entire back and is bent up round the borders. Two genera are distinguished: Argas, Latreille, 1796 (Rhynchoprion, Hermann, 1804), and Ornithodorus, Koch, 1844. The species live on mammals, but more especially on birds.

Genus. *Argas*, Latreille.

*Argas reflexus*, Fabricius, 1794.

Syn.: Acarus reflexus, Fabricius, 1794; A. marginatus, Fabricius, 1794; Rhynchoprion columbæ, Hermann, 1804.

The European marginated tick, Argas reflexus (length of male 4 mm., breadth 3 mm., length of female 6 to 8 mm., breadth 4 mm.), is of a yellowish colour and has yellowish-white legs. The ingested blood shows red or brown through the intestine, which is provided with blind sacs. It lives in dovecots. It remains hidden during the day and at night crawls on to the sleeping pigeons to suck their blood. It has been observed in France, England, Italy, Germany, and Russia. Persons sleeping near infected dovecots, or in apartments formed from pigeon-lofts, are also attacked, even when the room in question has not been used for sheltering pigeons for years, as “marginated ticks” can live in a fasting condition for a very long time. The bite sometimes gives rise to serious symptoms, such as general erythema and sudden œdema.

[This pest more often feeds on the blood of man than is imagined. Blanchard states that he has received them from men’s clothes in Strasburg. Boschulte, of Westphalia, records these parasites in a bedroom inhabited by children and connected with a pigeon-house. The children were bitten during sleep on the hands and feet. The result of the bite was intense itching along the nerves, the bite only being marked by a red spot. In a girl of 14 or 15, vesicles were formed similar to those produced by burns, and in an old man an ulcer formed. Others record painful punctures and persistent œdema produced by this pigeon pest. It was once abundant in Canterbury Cathedral, and often caused much annoyance, I am told, to the worshippers; the ticks falling down from the roof, where they were living, derived from the numerous pigeons that breed in the towers. This Acarus has enormous powers of vitality, living without food for months at a time.--F. V. T.]

*Argas persicus*, Fischer de Waldheim, 1824.

Of oval form and brownish-red colour. The male measures 4 to 5 mm. in length by 3 mm. in breadth; the female 7 to 10 mm. in length by 5 to 6 mm. in breadth. It frequents the entire north-west and north-east of Persia (the gerib-gez or malleh of the Persians, the miana bug of travellers). It lives concealed in houses and attacks man at night to suck his blood. Its bite is much dreaded, but the serious results may probably be attributed to unsuitable treatment of the wound or its invasion by bacteria.

[This tick, sometimes called the tampan and wandlius in South Africa, is mainly a fowl parasite. Fowls and ducks frequently die under its attack, particularly young ones, death being due to loss of blood. This tick remains attached to its host during its larval stage for about five days; it then leaves and moults in concealment. In its subsequent stages it visits its host by night and remains for about an hour only, during which time it distends itself fully with blood. As a nymph it moults twice, not once as do the cattle ticks. This tick and other Argas become larger with each moult, but retain their same general appearance. The female visits the host every now and then, and, between, deposits eggs in sheltered crevices. About fifty to 120 are deposited at once. Four weeks seems a necessary period to intervene between visits to the host, and the interval may be extended to upwards of a year according to Lounsbury.[346]

[346] “Report of Government Entomologist, Cape of Good Hope, for 1899,” 1900, p. 33.

[It is found in the Sudan, where Balfour has found granules derived from the segmentation of spirilla in their digestive tract. Fantham and Hindl have confirmed this. It has been assumed that these granules carry infection.

[This so-called Persian tick, the miana, which is such a scourge to travellers in Persia, appears to infest the huts of natives in that country. It has been sent me from Quetta, where it has invaded houses to such an extent the natives cannot live in them. The virulence of its bite is probably due to the tick transmitting fever germs from natives, probably inured, to strangers, who would be susceptible.--F. V. T.]

*Argas brumpti*, Neumann.

[Found in Somaliland, by Brumpt, and in the Sudan. This tick attacks man as well as wild animals and produces a painful swelling according to King,[347] but as pointed out by that naturalist it probably relies on other than human food.--F. V. T.]

[347] “Fourth Report Wellcome Res. Labs.,” 1911, p. 128.

*Argas chinche*, Gervais, 1844.

This Acarus, a native of the temperate parts of Colombia, is very troublesome to man. It is probably identical with A. americanus, Packard, which infests domestic fowls and turkeys, and occasionally also cattle, and is differentiated from A. reflexus by the sculpturing of the cuticle.

Genus. *Ornithodorus*, Koch.

Neumann’s SYNOPSIS OF THE GENUS ORNITHODORUS is as follows:--

{ Hypostome unarmed; integument in nymph stage and 1 { partly in adult spinulose MÉGNINI. { Hypostome armed with recurved teeth; integument { not spinulose 2. 2 { Camerostome with movable lateral flaps TALAJE. { Camerostome without movable lateral flaps 3. { Anterior border of distal segments of legs with 3 { tubercles or festoons 4. { Anterior border of segments of legs without { tubercles or festoons 8. 4 { Body not much contracted anteriorly 5. { Body pointed anteriorly 7. { Tubercles of distal segments of legs higher than { broad, distant 6. 5 { Festoons of distal segments of legs as broad as { high, contiguous pavimentosus. 6 { Eyes present SAVIGNYI. { No eyes MOUBATA. 7 { Eyes present coriaceus. { No eyes TURICATA. 8 { Integument with fine radiating wrinkles lahorensis. { Integument granular 9. 9 { Tarsi appearing bifid at apex furcosus. { Tarsi not appearing bifid at apex 10. { Tarsi of first pair of legs with three dorsal 10 { tubercles, of other legs with one canestrinii. { Tarsi without dorsal tubercles or with only one 11. { Tarsi of last three pairs of legs with pronounced 11 { dorsal protuberance tholozanii. { Tarsi of legs with indistinct dorsal protuberance erraticus.

*Ornithodorus moubata*, Murray, 1877.

An abundant African tick which is one of the carriers of the spirillum of African relapsing fever and can also carry Filaria perstans (Christy). Its body is oval, yellowish-brown when young, greenish-brown when mature. The integument is covered with mamillose tubercles. No eyes and the stout legs granular above, the tibiæ and tarsi fringed with tubercles on the upper side. Pocock[348] records it from Uganda and German East Africa, Congo and Angola, to Namaqualand and the Transvaal in the south. It is called bibo in Uganda, moubata in Angola, and tampan on the Lower Zambesi. It feeds on animals and birds as well as man. Its bite is very painful. This tick is found in native huts, living in cracks and crevices and in the thatch roofs.

[348] “A System of Medicine,” Allbutt and Rolleston, i, pt. 2, p. 195.

The female tick infected with the spirillum transmits the infection to the eggs and the next generation. They appear to be able to live without food a long time, and probably live for years. They lay their eggs in masses on the ground or in crevices, and when they hatch they are in the nymph stage with four pairs of legs. O. moubata also occurs in Madagascar with recurrent fever (Lamoureux, Bull. Soc. Path, exot., 1913, vi, No. 3, pp. 146–149).

*Ornithodorus savignyi*, Audouin, 1827.

At one time considered the same as the preceding species, but can be easily separated by the presence of two pairs of eyes. It is widely spread over Africa and has been found in South India and at Aden. In the Sudan it occurs in large numbers. King[349] records that a few miles N.N.E. of Khartoum 370 specimens were collected in two hours under a single tree by a well. It is found in Somaliland, where relapsing fever occurs and no O. moubata, which it probably replaces as a transmitter (Drake-Brockman, “Rep. Col. Office,” April 6 and April 16, 1913). It also occurs in Tunis, where the natives call it “tobbiah” (Weiss, Arch. de l’Inst. Pasteur de Tunis, 1912, pt. 4, p. 226).

[349] “Fourth Report Wellcome Res. Labs.,” 1911, B, p. 129.

*Ornithodorus coriaceus*, Koch.

Found in Mexico, Paraguay and California. Attacks man.

*Ornithodorus talaje*, Guerin, 1849.

An eyeless species with somewhat elongate pentagonal body found in Mexico and South America, called the “chinche.” A variety of it (coniceps) is found at Venice, etc., and another variety on various islands in the Indian Ocean and South Atlantic. Its bite is very painful to man.

*Ornithodorus turicata*, Dugès, 1876.

Without eyes. Indigenous in Central America; attacks human beings and pigs. The bite is painful and is often followed by serious consequences.

[So virulent is this species that pigs put in an infested sty often die in a night. This “turicatas” of Mexico often reaches 6 mm. in length.--F. V. T.]

*Ornithodorus tholozani*, Laboulbène and Mégnin, 1882.

Syn.: Argas tholozani, Lab. and Még., 1882.

Without eyes. Males 4 to 6 mm. in length and 2 to 4 mm. in breadth; females 8 to 10 mm. in length and 4 to 5 mm. in breadth. It especially attacks sheep. Native of Persia and Asia Minor.

[This species is reputed as being very dangerous to man. It is locally know as the kéné, or sheep-bug. In its fully gorged state it is deep violet.--F. V. T.]

*Ornithodorus mégnini*, Dugès, 1883.

Syn.: Argas mégnini, Dugès, 1883.

Length 8·5 mm., breadth 5·5 mm. Native of Mexico.

[Another synonym for this species is Rhynchoprion spinosum, Marx. The adult males and females are grey to dark brown, the male somewhat the smaller; female 5 by 3·5 by 2·5 mm. to 10 by 6 by 3·5 mm. The larvæ at the seed tick stage are dark grey, turning to pink, then to a whitish grey when engorged. The nymph when young is blood-red in front, rest pearly white; later they turn reddish-brown.

[Intense pain may be caused by its presence in and around the ears.

[Two specimens in the nymphal state were taken from the ears of a visitor to Cambridge by Dr. J. Christian Simpson. They were supposed to have entered the ears when the gentleman was camping out in Arizona (Lancet, 1901, i, No. 4,052, p. 1198, fig. 3).

[This species attacks the horse, ass, dog, cats and oxen, generally around the ears, and also attacks man. It is well known in the United States as infesting the ears of children (New York Ent. Soc. Journ., 1893, pp. 49–52).

[It occurs in Texas, Arizona, New Mexico and California as well as Mexico, Brazil, and possibly many parts of South America; and recently Bedford (“Sec. Report Div. Vet. Res., S. African Union,” 1912, pp. 343, 344) has shown it to occur at Vryburg and Fauresmith, in the Transvaal, on stock. It also occurs in the Sudan.--F. V. T.]

OTHER LITERATURE ON Ixodidæ.

(1) “Pénétration de l’Ixodes ricinus sous la peau de l’homme,” Compt. rend. Soc. de Biol., 1891, xliii, ser. 9, iii, pp. 689–691, R. Blanchard.

(2) “Notas sobre Ixodidas brazileiros,” _Mem. Inst. Oswaldo Cruz_, 1911, iii, fasc. 2, pp. 145–195, pls. 11 and 12, Dr. H. de Beaurepaire Aragão. Table of Brazilian Species.

(3) “Contribuicão para a sistematica e biolojia dos Ixodidas,” _Mem. Inst. Oswaldo Cruz_, 1912, iv, fasc. 1, pp. 96–120, pls. 2 and 3, Dr. H. de Beaurepaire Aragão.

Family. *Tyroglyphidæ.*

Very small mites without eyes and without tracheæ, with smooth skin.

The males usually have a suctorial pore on either side of the anus, which is used during copulation, or suckers may be found in both sexes near the sexual orifice. The mouth parts form a cone with chelate cheliceræ, and three-jointed pedipalpi; the legs are usually short, have five segments with a terminal claw and suckers, or either one or other of these organs. The numerous species and genera live free and from choice in slowly decomposing vegetable and animal matter (cheese, cereals, flour, sugar, preserves, dried anatomical preparations, bacon, dried fruits and fungi), also in the corners of dwellings, etc.; they incidentally get into or on to man, or are found in chamber utensils and in spittoons; actual parasites are rarely found amongst them.

[The chief genera are Tyroglyphus, Rhizoglyphus, Glyciphagus, Aleurobius and Histiogaster. The first three have typical characters referred to, but are distinguished from each other by the two former having the hairs on the dorsum smooth, whilst in Glyciphagus they are hairy, plumose, or feathered. Rhizoglyphus can be told from Tyroglyphus by having claws on the tarsi without any suckers; Tyroglyphus has both claws and suckers. The larvæ are hexapod and may become adult in the usual way by repeated moults, or they enter the so-called hypopial stage. In this the eight-legged nymph becomes quiescent, and during this stage it fixes itself to some insect or other animal by a patch of suckers on the lower surface of the hind end of the body, and is so carried from place to place. The hypopus does not feed and has a hard shell and short legs. When it has reached a new home it moults and development proceeds in the normal way. Canestrini and Kramer treat the Tyroglyphidæ as a sub-family of the Sarcoptidæ, calling them sub-family Tyroglyphinæ, the other sub-families being Sarcoptinæ, Canestriniinæ and Analsinæ.--F. V. T.]

Sub-family. *Tyroglyphinæ.*

Genus. *Aleurobius*, Canestrini.

*Aleurobius* (*Tyroglyphus*) *farinæ*, de Geer (part), Koch.

The male measures 0·33 mm. in length by 0·16 mm. in breadth; the female 0·6 mm. in length by 0·3 mm. in breadth. These mites possess five pairs of suctorial organs of a light colour; the legs are reddish. Moniez observed them in Lille on the skin of labourers who had been unloading Russian corn. A few of the species generally mentioned under the designation of Tyroglyphus siro are probably the common flour-mite, which also occurs on dry cheese.

[The farinæ of de Geer is an Aleurobius described by him in 1778 (“Mém. Hist. Ins.,” vii, t. 5, f. 15, p. 97) as Acarus farinæ.--F. V. T.]

Genus. *Tyroglyphus*, Latreille.

*Tyroglyphus siro*, L., 1756.

(Defined by Gervais, 1844.)

Male 0·5 mm. in length by 0·25 mm. in breadth; female 0·53 mm. in length by 0·28 mm. in breadth; the males have two suckers on the tarsi of the fourth pair of legs. Penis straight, colour whitish or reddish.

*Tyroglyphus longior*, Gervais, 1844.

White or yellowish, with two black spots on the abdomen. Male 0·55 mm. in length, 0·28 mm. in breadth; penis bent. Female 0·61 mm. in length and 0·28 mm. in breadth.

T. siro and T. longior live on dry cheese, in flour, on dried fruits, etc., and have been occasionally observed in the stools, urine, or pus of human beings, and also on their skin. The so-called vanillismus is to be attributed to these species.

[T. siro and T. farinæ of Schrank (non Geer) are the same. They are described under other names, such as Acarus lactis, Linn.; A. favorum, Herm., etc.; A. lactis in milk, farinæ in flour, and siro in cheese; and as A. dysenteriæ, Linnæus (“Syst. Nat.,” ed. 12, pp. 1024–1767).]

It is to these species that a case of dysentery was referred. Rolander, who studied under Linnæus, was attacked by what was called dysentery. The complaint soon gave way to treatment, but eight days after it returned, soon disappeared, but again came a third time. All the time Rolander had been living like the other inmates of the house, who all escaped. Linnæus, aware that Bartholemy had attributed dysentery to insects which he said he had seen, advised his student to examine his stool. The result was that innumerable mites were found to be present. Their presence was easily accounted for by the fact that they were found in numbers in a cup made of juniper wood from which the student alone drank of a night, and they were found to be of the same species. What this species is we do not know. Linnæus called it Acarus dysenteriæ, but it was the same as his Acarus siro. No records have occurred since. It cannot be, as Latreille supposed, the cheese mite, for they have been eaten by millions since, and it is strange no such case has occurred again.

[*Tyroglyphus minor* var. *Castellani*, Hirst,

causes the copra itch in persons employed in the copra mills in Ceylon. The skin of the hands, arms, legs and even body becomes covered with pruriginous papules, papulo-pustules and pustules near the head. The eruption begins as a rule on the hands. The mites live in the copra dust. They produce dermatitis. Castellani produced the disease experimentally by rubbing copra dust containing mites on the skin of healthy people. Beta-naphthol ointment (5 to 10 per cent.) proved useful in treatment (Journ. Trop. Med. and Hyg., December 16, 1912, Castellani and Hirst).--F. V. T.]

Genus. *Glyciphagus*, Hering, 1838.

*Glyciphagus prunorum*, Her., and *G. domesticus*, de Geer.

The Glyciphagi are differentiated from the Tyroglyphi in that the chitinous hairs on the body are fringed or feathered, and that they lack a furrow dividing the cephalothorax from the abdomen. They live under similar conditions to the Tyroglyphi and are occasionally found on man or in fæces.

[Sugar merchants and grocers are frequently troubled by swarms of G. domesticus, which leave the stores when being handled, and especially shopmen, who handle sugar kept in small stores for some time. These are the Acari that cause that irritating temporary affection known as “grocer’s itch.”--F. V. T.]

*Glyciphagus cursor*, Gervais.

Under this name Signor Moriggia figures a horny excrescence of great length growing from a woman’s hand, and containing in its cavities quantities of Acarus. This species is really G. domesticus, de Geer. G. domesticus has also been described by Gervais (Ann. Sci. Nat., 1841, ser. 2, xv, p. 8) as G. hippopodes.

*Glyciphagus buski*, Murray.[350]

[350] Cooper and Busk’s Micros. Journ., 1842, and “Economic Entomology,” Murray, p. 280.

[This is a mite found by Busk and named after him by Murray. It was taken from beneath the cuticle of the sole of the foot of a negro in the Seamen’s Hospital Ship on the Thames in 1841, in large sores of a peculiar character confined to the soles of the feet. It appeared that the disease was caused by its burrowing beneath the thick cuticle. The disease was attributed to the wearing of a pair of shoes which had been lent to another negro whose feet had been similarly affected for nearly a year. The negro to whom the shoes were lent came from Sierra Leone. Mr. Busk stated that some water brought by Dr. Stranger from the River Sinoe, on the coast of Africa, contained one nearly perfect specimen, and fragments of others very similar to if not identical with this Acarus. Mr. Busk adds that he had been informed by Staff-Assistant Surgeon P. D. Murray that at Sierra Leone there is a native pustular disease called craw-craw--a species of itch breaking into open sores.

[From Busk’s original figure I see no reason to doubt that this is a Glyciphagus.--F. V. T.]

Genus. *Rhizoglyphus*, Claparède, 1869.

*Rhizoglyphus parasiticus*, Dalgetty, 1901.

The Rhizoglyphii are to be recognized by their short legs, which are beset with spines, and by the tarsi, which terminate in a claw. They live on plants, roots and bulbs, especially the bulbs of lilies.

This species has been observed on the feet of Indian coolies working in the tea plantations; they produce a skin disease which always commences with blebs between the toes, and which almost always extends to the malleoli, but not beyond. The Acari have an elliptical body, which is grey, but varies from greenish-yellow to greenish-brown when the stomach is full. Eyes are absent. The legs are composed of five segments and terminate with a claw. The males measure 0·18 mm. in length by 0·08 mm. in breadth, and possess genital and anal pores; the females measure 0·2 mm. in length by 0·09 mm. in breadth.[351] [This is also known as coolie itch and is common in Indian tea plantations.--F. V. T.]

[351] Dalgetty, A. B., “Water-itch; or Sore Feet of Coolies,” Journ. Trop. Med., 1901, iv, p. 73.

Genus. *Histiogaster*, Berlese, 1883.

*Histiogaster* (*entomophagus?*) *spermaticus*, Trouessart, 1900.

The genus Histiogaster, which also approaches the Tyroglyphinæ, is characterized by the circumstance that the males possess suctorial pores used in copulation, as well as leaf-shaped appendages at the posterior end of the body. They feed on vegetables, especially on small fungi.

This species has been described by Trouessart,[352] who found numerous specimens, some adult, others in the developmental stage (larvæ, nymphs), and ova, in the fluid removed by puncture from a cyst of the right testis. The males measure 0·25 mm., the females 0·32 mm., and the larvæ 0·1 mm. in length. The author is of opinion that the animal--perhaps a fertilized female--was introduced by a catheter, and, as a matter of fact, it was afterwards found that the patient had once had the catheter passed in India while suffering from pernicious fever.

[352] Trouessart, E. R., Compt. rend. Soc. Biol., Paris, 1900, lii, pp. 742–744, 893, 894; Arch. de Par., 1902, v, pp. 449–459.

It would here rather appear to be the case of a facultative parasitism of an otherwise free-living species. Histiogaster entomophagus, Laboulbène, is found occasionally in collections of insects feeding on larger species containing much fat; the species also occurs on dry cantharides; it appears to belong to the region of South Europe, where, however, it is widely spread.

[Entomophagus occurs all over Europe and in America. It has been described under the following names: Acarus malus, Shimer, 1868 (Trans. Illinois Hort. Soc.); Dermaleichus mali, Riley, 1873 (Rep. Ins. Missouri, v, p. 87); Tyroglyphus mali, Murray, 1877 (“Eco. Ent. Apt.,” p. 275); T. corticalis, Michael, 1885 (Trans. Roy. Micros. Soc., ser. 2, v, 3, p. 27, figs. 1 to 14); Histiogaster corticalis, Canestrini, 1888 (Prosp. Acarof., iii, p. 397); H. aleurophagus, Sicherin, 1894, Canestrini, Prosp. Acarof., vi, p. 815. Trouessart’s species is evidently distinct.--F. V. T.]

Genus. *Cheyletus.*

*Cheyletus mericourti*, Lab.

Acaropsis mericourti, Moq. Tand.

[This mite has been described from three specimens found in pus which flowed from an abscess in the ear of a naval officer, produced by inflammation of the auditory passage. Where the mites came from we do not know, as they were found near the Bank of Newfoundland. This genus of Acari has enormous mandibles and a peculiar tracheal system; two ungues and appendages to the tarsi.--F. V. T.]

Family. *Sarcoptidæ* (Itch Mites).

Small mites without eyes and tracheæ, and with delicate, transversely striated cuticle. The mouth parts form a cone, over which the shield-shaped upper lip protrudes; the cheliceræ are chelate; the pedipalpi (or maxillary palpi) have three joints; the legs are short and compact, and composed of five segments; the terminal joints have pedunculated suckers (ambulacra) or a long bristle. The larvæ are six-legged. They live on or under the skin of birds and mammals, on which they produce the skin disease known as scabies, or itch.

[The Sarcoptidæ attack the hairs, feathers or epidermis of birds, animals and man, living as permanent parasites. The punctures they produce are followed by the formation of more or less thick crusts or scabs, beneath which the mites live and breed (so called scab, mange and itch). Most are oviparous, some ovoviviparous. The eggs are minute, ovoid, with a thin semi-transparent shell. They incubate in a few days, varying from two to ten or eleven, as a rule. Generally sarcoptic diseases lie dormant in winter and revive in spring and summer in man; but in animals with long wool, such as sheep, they are most active during winter, although revival of active reproduction takes place in spring.

[Speaking generally, for the Sarcoptidæ there are three distinct stages in the development of the male, four in the female, as follows:--

[(1) The larva. In this stage only three pairs of legs occur.

[(2) The nymph, in which a fourth pair of legs appear, and which thus approaches the adult; but so far no sexual organs occur. Nymphs are of two sizes--the smaller being future males, the larger females.

[(3) The next stage in the female is the age of puberty, the female now being provided with a vulvo-anal slit; this so-called pubescent female is fertilized by the male. The male then dies. But the female again casts her skin and enters another stage--

[(4) The ovigerous female--the egg-laying female--which has differently modified legs.

[The rate at which these Acari breed is very great. Gerlach has found that roughly, in each Sarcopt gallery, a female produces fifteen individuals--ten females and five males--and that the progeny reproduce again in fifteen days. The table given below thus shows that one pair may produce the enormous number of 1,500,000 descendants in three months:--

First generation after 15 days 10 females 5 males Second " " 30 " 100 " 50 " Third " " 45 " 1,000 " 500 " Fourth " " 60 " 10,000 " 5,000 " Fifth " " 75 " 100,000 " 50,000 " Sixth " " 90 " 1,000,000 " 500,000 "

= 1,500,000 individuals.

[These Acarinæ are divided into three distinct sub-families, namely the Cytolichinæ, Sarcoptinæ, Canestriniinæ.

[The Sarcoptinæ alone interest us here, and of the nine genera the three following are the most important:--

[(1) Sarcoptes, Latreille; Eusarcoptes.

[(2) Psoroptes, Gerv.; Dermatodectes, Gerlach; Dermatocoptes, Fürstenberg.

[(3) Chorioptes, Gerv.; Symbiotes, Gerlach; Dermatophagus, Fürst.; Sarco-dermatocedes, Del.

[The following are the main characters of these three genera:--

[Sarcoptes--round or slightly oval; the two posterior pairs of legs being nearly or quite concealed beneath the body; the tarsi end in simple long pedicles, with ambulatory suckers.

[Psoroptes--oval; the legs are all visible outside the margin of the body; the ambulatory suckers are carried on long triangulated stalks; the male has copulatory suckers and abdominal prolongations.

[Chorioptes--oval; legs long, thick, all visible; ambulatory suckers very wide, carried at the end of simple, short pedicles.

[Sarcoptes make channels or furrows beneath the epidermis, and in these the female lays her eggs. This form of acariasis is thus difficult to cure. It is the cause of human itch (vide Sarcoptes scabiei).

[Psoroptes do not make sub-epidermic galleries; they live and breed in colonies beneath crusts or scabs formed by the changes they produce in their host’s skin. Sheep scab is a common type of disease produced by Psoroptes. This genus is of little importance as a parasite to man.

[Chorioptes live as Psoroptes; they also do not affect man. Otodectes, Can., affecting cats and dogs, and others occur, but do not affect man as far as we know at present (“Demodicidae und Sarcoptidae,” von Professor G. Canestrini und P. Kramer, _Das Tierreich_, 1899).--F. V. T.]

Sub-family. *Sarcoptinæ.*

Genus. *Sarcoptes*, Latreille.

*Sarcoptes scabiei*, de Geer, 1778.

Syn.: Acarus scabiei, de Geer, 1778; A. psoricus, Pallas, 1760; A. siro, L., 1778; Sarcoptes exulcerans,? Linn., 1758, Nitsch, 1818; S. hominis, Raspail, 1834, and Hering, 1838; S. galei, Owen, 1853; S. communis, Delaf. et Bourg., 1862; S. scabiei var. hominis, Mégnin, 1880.

The body is oval or nearly circular and whitish in colour, with transverse rows of striæ partly interrupted on the back. There are transverse rows of small bristles on the dorsal surface, and groups of trichomæ on the front, sides and back. There are chitinous hairs at the base of the legs; the two first pairs are provided with pedunculated ambulacra in both sexes, the two posterior pairs terminate each with a long bristle in the female; in the male the third pair of legs terminate in a bristle, the fourth pair with a pedunculated ambulacrum. The anus is situated at the posterior border of the dorsal surface.

At one time numerous species were differentiated, according to the form of the Acarus, the number, position and size of the hairs and spines, even according to the hosts, etc. All these characteristics, however, fluctuate so considerably that absolute differentiation is impossible; the supposed species may be regarded in the same light as Mégnin did, as varieties. It is also hardly possible to distinguish the mite of human scabies (S. hominis) from that of a number of domestic animals (S. squamiferus). It is best, therefore, to accept one single species (S. scabiei), which may give rise to different races or castes by living in the skin of man and mammals, but can pass from one host to the other.

[Canestrini and Kramer, in their monograph of the Sarcoptidæ, enumerate eighteen distinct species of this genus, from the dog, goat, camel, horse, ferret, lion, wolf, sheep, pig, etc., and two species parasites of man (scabiei and scabiei-crustosæ). There is no doubt that they are distinct species.--F. V. T.]

The S. scabiei of man (S. scabiei var. hominis) (length of male 0·2 to 0·3 mm., and breadth 0·145 to 0·190 mm.; length of female 0·33 to 0·45 mm., and breadth 0·25 to 0·35 mm.) lives in the tunnels that it excavates in the epidermis, and attacks by preference places with thin skin, such as between the fingers, in the bend of the elbows and knees, in the inguinal region, on the penis, on the mammæ, but may also affect other parts. The tunnels, which vary from a few millimetres to a centimetre and more long, do not run straight, but are somewhat tortuous; the female is found at the terminal end. The tunnels contain the excrement and oval eggs (0·14 mm. in length) of the parasite; the males are rarely met with, as they die off after copulation; the females die after depositing their eggs. The six-legged larvæ hatch out after four to eight days, and after about a fortnight, during which time they change their skins three times and undergo metamorphosis, they begin themselves to burrow. Transmission from person to person rarely is effected through linen, but by direct contact (as in coitus); transmission can be artificially effected on horses, dogs and monkeys, but not on cats.

The smaller S. scabiei-crustosæ, Fürstenberg, is the cause of the itch that occurs chiefly in Norway; it is not certain whether this is a distinct species of itch mite.

[This is quite a distinct species, which is recorded from Germany and France. Mégnin (Parasitology, 1880, p. 165) described this as S. scabiei var. lupi. The female is 140 µ long, 340 µ broad; the male is 170 µ long by 150 µ broad. In Science (March 3, 1893, p. 125) is recorded that at the Indiana Academy of Science Dr. Robert Hessler referred to “a case of that extremely rare and almost extinct form of itch known as ‘Norway itch,’ the scabies norvegica of Hebra, 1852.” The afflicted man was covered with thick, creamy white, leathery scales; some of these scales measured over an inch in diameter and 1/10 in. thick. A constant shedding of scales went on, a handful being gathered daily. They were found full of mites and eggs and riddled with passages. Under treatment the mites were killed and the skin became normal. Dr. Hessler made a calculation of the number of eggs and mites, amounting to ova and shells 7,004,000, mites in all stages 2,009,000.--F. V. T.]

The following forms may be transmitted from DOMESTIC ANIMALS to MAN:--

(1) S. scabiei var. equi. Male, 0·2 to 0·23 mm. long, 0·16 to 0·17 mm. broad. Female, 0·40 to 0·42 mm. long, 0·28 to 0·32 mm. broad. The horse is the normal host.

(2) S. scabiei var. ovis. Male, 0·22 mm. long, 0·16 mm. broad. Females, 0·32 to 0·44 mm. long, 0·24 to 0·36 mm. broad. This mite lives on sheep, and passes over to goats and human beings; it may also be artificially transferred to horses, oxen and dogs.[353]

[353] [This mite produces the so-called “black muzzle” of sheep.--F. V. T.]

(3) S. scabiei var. capræ. Male, 0·24 mm. long, 0·188 mm. broad. Female, 0·345 mm. long, 0·342 mm. broad. On goats, passing from them to horse, ox, sheep, pig and man. On the latter, in contradistinction to the varieties (1) and (2), it produces a severe affection.

(4) S. scabiei var. cameli. Frequently observed in man, chiefly in Africa. A few cases have been observed in Europe; the affection induced by it is severe.

(5) S. scabiei var. aucheniæ. Male, 0·245 mm. long, 0·182 mm. broad. Female, 0·34 mm. long, 0·264 mm. broad. It lives on the llama, and may be transmitted to man.

(6) S. scabiei var. suis. Male, 0·25 to 0·35 mm. long, 0·19 to 0·3 mm. broad. Female, 0·4 to 0·5 mm. long, 0·3 to 0·39 mm. broad. In the domestic pig and wild boar; occasionally also in man. The settlement, however, is usually of short duration.

(7) S. scabiei var. canis. Male, 0·19 to 0·23 mm. long, 0·14 to 0·17 mm. broad. Female, 0·29 to 0·38 mm. long, 0·23 to 0·28 mm. broad. In the house-dog, and also, not unusually, in human beings.

(8) and (9) S. scabiei var. vulpis and S. scabiei var. leonis of the fox and lion have likewise been observed on man.

These are all distinct species and should read as follows: S. canis, Gerl.; S. ovis, Mégn.; S. equi, Gerl.; S. dromedarii, Gerv. (cameli, Mégn.); S. aucheniæ, Raill.; S. suis, Gerl.; S. vulpis, Fürst.; S. leonis, Can.

*Sarcoptes minor*, Fürstenberg, 1861.

Anus situated on the back, legs short, pedunculated ambulacra broad; living on cats (S. minor var. cati) and rabbits (S. minor var. cuniculi). In cats this mite usually lives in the cervical region, and thence spreads to the ears and head; it usually causes the death of the infected animals; it is easily transferable from cat to cat, is difficult to transmit to rabbits, but once settled on them can easily infect other rabbits. On the other hand, the transmission of the itch mite of the rabbit to the cat does not succeed. In man S. minor induces an eruption that disappears after about a fortnight.

[S. minor, Fürstenberg, 1861 (“Krätzm.,” viii, p. 218), comes in Railliet’s sub-genus NOTOEDRES, 1893 (“Zool.,” ed. 2, p. 660). Canestrini raised this to generic rank in 1894 (Prosp. Acarof., vi, p. 724).

[There are three species: (1) N. notoedres, Mégnin = Sarcoptes alepis, Railliet and Lucet (Compt. rend. Soc. de Biol., 1893, xlv, p. 404), and Sarcoptes notoedres var. muris, Mégnin (Parasitology, 1880, pp. 172–174). This occurs on the black and brown rats and the water-vole.

[(2) N. cati, Hering, 1838 (N. acta. ac. Leop., ii, 18, xliv, p. 605, figs. 9 and 10), = Sarcoptes minor, Fürstenberg (“Krätzm.,” 1861, viii, p. 215). Found on the cat in Germany, France, Italy, and Britain.

[(3) N. cuniculi, Gerlach, 1857, “Krätzm.,” iii, figs. 20, 21. It lives on the rabbit and is found in Germany and France.--F. V. T.]

The itch mites of domestic animals, which belong to the genera Psoroptes (= Dermatodectes = Dermatocoptes) and Chorioptes (Symbiotes = Dermatophagus), as a rule do not infest and live on man, even when artificially transmitted. It is, however, possible for this to occur. Moniez (“Traité de par.,” 1896, p. 559) mentions that a species of Chorioptes--probably Ch. bovis--had been found on man, as had also Demodex folliculorum. This author also includes Dermatophagoides scheremetewskyi, Bogdanoff (Bull. soc. imp. d. natural., Moscou, 1864, xxxvii, p. 341), which has repeatedly been found on man in Moscow and Leipzig (Zürn, Ber. d. med. Ges., Leipzig, 1877, p. 38), as Chorioptes bovis.

OTHER REFERENCES TO Scabies crustosæ AND norvegica, ETC.

(1) “Ein Fall von Scabies crustosa norvegica,” Würzb. med. Zeitschr., l, pp. 134–139, pl. 3, H. Bamberger.

(2) “Ueber die Krätzmilbe (Acarus scabiei),” Notiz. a. d. Geb. d. Nat. u. Heilk., Weimar (1913), xlii (11), Oct., pp. 161–166 (1834), de Blainville.

(3) “Rapport sur le ciron de la gale (Acarus scabiei),” Ann. de Mus. d’Hist. nat., 1831; Parasitology, iv, pp. 213–232, de Blainville.

Family. *Demodicidæ* (Mites of the Hair-follicles).

Small Acarina, elongated in worm-like fashion, with annulated abdomen, and without eyes or tracheæ. The mouth parts consist of a suctorial proboscis and three-jointed palpi; the legs are short, and have three segments with small terminal ungues. The anus is situated on the anterior border of the abdomen; oviparous; the larvæ have six stumpy legs. These mites live in the hair-follicles of mammals.

Genus. *Demodex*, Owen.

*Demodex folliculorum*, Simon, 1842.

Syn.: Acarus folliculorum, Sim., 1843; Demodex folliculorum, Owen, 1843; Macrogaster platypus, Miescher, 1843; Simonea folliculorum, P. Gervais, 1844; Steatozoon folliculorum, Wilson, 1847.

As in Sarcoptes scabiei, numerous varieties of this species are known; the form parasitic on man lives in the hair-follicles, the meibomian and sebaceous glands, and hardly ever causes inconvenience; the male measures 0·3 mm. in length and the female about 0·4 mm. in length. The eggs 0·06 to 0·08 mm. in length, 0·04 to 0·05 mm. in breadth, and are thin-shelled. The creatures are always attached with the head end downwards in the parts mentioned; they are most frequent in the sebaceous glands of the face, by the nose, lips and forehead, but they may be present on the abdomen and on other parts of the body. They may occasionally obstruct the excretory gland ducts, thus causing inflammation of the gland (comedones); their agglomeration in the meibomian glands sets up inflammation of the margins of the eyelids. There are generally only a few specimens in a gland. According to some statements Demodex occurs in 50 per cent. of mankind and even in children; they survive the death of their hosts by several days.

The variety living in the dog (D. folliculorum var. canis) is smaller than the variety living in man, and produces a skin disease resembling scabies in these animals. According to Zürn they may also live on man; nevertheless, no other investigator has recorded a similar observation, and attempts at artificial infection have proved negative.[354]

[354] [This mite causes what we know in England as red mange in dogs.--F. V. T.]

[Ten distinct species of Demodex are given by Canestrini and Kramer (“Demodicidae und Sarcoptidae,” Das Tierreich, 1899, vii). The species are certainly distinct.

[The species living on the dog (D. canis, Leydig, 1844) is cosmopolitan. According to the British Medical Journal (February 22, 1913, p. 407), dog mange may be caught by humans. Whitfield and Hobday describe in the Veterinary Journal seventeen cases which have come under their observation.--F. V. T.]

Order. *Pentastomida.*

Family. *Linguatulidæ.*

Arachnida greatly altered in consequence of their parasitic manner of life; for a long time they were regarded as helminthes. The body is elongated, vermiform, flattened or cylindrical, and more or less distinctly annulated. The head, thorax, and abdomen are not defined from each other (fig. 371). The elliptical mouth, surrounded by a chitinous ring, is situated at the anterior end, on the ventral surface, and the intestine leading straight through the body opens at the posterior end. Two retractile hooks are at the sides of the mouth (fig. 372); these are usually considered to be the terminal joints of two pairs of legs, but it appears to be more correct to regard them as the remains of the antennæ and palpi (Stiles). According to this opinion, the legs in the adult state are completely degenerated.

The nervous system is reduced to an œsophageal ring. No organs of sense are recognizable except the papillæ at the anterior end. There are neither organs of circulation nor of respiration.[355]

[355] What are designated as stigmata in the Linguatulides are the orifices of sebaceous glands.

The sexes are distinct. In the small male the sexual orifice is situated ventrally in the anterior part of the body; in the female it is placed near the anus. The Linguatulidæ lay eggs, and from each egg, after being conveyed into an intermediate host, a four-legged larva, with rudimentary mouth parts, hatches out. It goes through a series of metamorphoses, and passes through a second larval condition, which, however, possesses the essential characteristics of the fully developed form. Sooner or later it migrates during this stage, and reaches its final host, mammal or reptile, in the nostrils or lungs of which the adult Linguatulidæ live.

[As adults they live as internal blood feeders in various birds, reptiles and mammals, especially in the nasal and respiratory passages. The larval stage occurs in another host in an encysted condition; this host is usually an animal preyed upon by the species in which the sexual forms are found. The larvæ bore through the walls of the host’s stomach and enter liver and spleen or brain, where they encyst; here they grow until they assume almost the appearance of the adult. These encysted larvæ on being eaten later make their way into the nasal passages and lungs, where they mature. Both adults and larvæ occur in man, as mentioned later.

[Three genera are recognized in this family:--

[(1) Linguatula.--Body flat, annulated. Adults live in the nasal sinus.

[(2) Porocephalus.--Body cylindrical, elongate, with often deeply cut rings. Adult in respiratory organs of snakes, larvæ in animals and man.

[(3) Reighardia.--Cylindrical, but not ringed. Not found in humans.--F. V. T.]

Genus. *Linguatula*, Fröhlich.

*Linguatula rhinaria*, Pilger, 1802.

Syn.: Tænia rhinaria, Pilger, 1802; Polystoma tænioides, Rud., 1810; Linguatula tænioides, Lam., 1816; Pentastoma tænioides, Rud., 1819.

The male is white in colour, 18 to 20 mm. in length, anterior portion 3 to 4 mm. in breadth, posterior part 0·5 mm. in breadth. The female is of a yellowish colour, 8, 10, or 13 cm. long, anterior part 8 to 10 mm. and posterior part 2 mm. wide. The brownish eggs can be seen in the median line. The body is elongated, rather flat, and exhibits about ninety rings or segments with crenellated borders. The hooks round the mouth are strongly curved and are articulated to a basilar support. Eggs oval, 0·09 µ in length, 0·07 µ in breadth.

L. rhinaria, in the adult condition, lives in the nasal cavity and frontal sinus of the dog, wolf, fox, horse, goat, and occasionally of man; it causes severe catarrh, epistaxis and suppuration.

Development.--The ova, which are found in masses in the nasal mucus, already possess an embryo; they are expelled with the nasal secretion, and are swallowed by herbivorous mammals with their food, mostly by hares and rabbits, but also by sheep, goats, oxen, horses, antelopes, fallow deer, pigs, cats, and occasionally also by human beings. The young larvæ hatch out in the stomach; they possess a thickened anterior body with rudimentary mouth parts and two pairs of limbs; the body gradually tapers to a short tail.

The larvæ of the Linguatulidæ bore through the intestinal wall and reach the liver, more rarely the mesenteric glands, etc.; they here become encysted and enter a sort of pupal stage in which they lose their limbs; after several moultings and gradual growth the second larval stage, having the appearance of the adult Linguatula, sets in. About five to six months after infection the creatures have become 4 to 6 mm. long, possess eighty to ninety rings, which have a series of fine points on their posterior border; the mouth and intestine are formed, the sexual organs mature and the two pairs of hooks are near the mouth. This larval stage (fig. 372) has been known for a long time, but it was regarded as an independent species of animal, and therefore had a separate name (Linguatula serrata, Fr.; Pentastoma denticalatum, Rud., etc.).

Later these Linguatula larvæ make an attempt to escape from their hosts, and this, of course, can only be effected by means of an active migration; they leave the cysts, and according to their respective positions in the abdominal or pleural cavities they reach the bronchi or the intestine, and finally pass out; they may be again sniffed up by dogs and settle in their nasal cavities. Still this outward migration does not appear to be necessary for further development. A portion of the larvæ gain access to the nasal cavities directly through the trachea, and thus herbivorous mammals certainly become directly infected. In most cases the infection of dogs, wolves and foxes, that is, of carnivorous mammals, takes place through consuming the bodies of mammals, or parts of them, such as the liver and lungs, which are affected with the second larval form; in any case most larvæ obtain access first to the stomach of their host, from here they make an active migration through the œsophagus to the oral and nasal cavities, in which they settle. It is possible also that the same larvæ which are free in the oral cavity when the food is being eaten migrate into the nasal cavities. After being stationary a fresh skin is formed and the spine-bearing cuticula are thrown off. The male attains its full size in the fourth, and the female in the sixth month. The duration of life is stated to be from fifteen months to several years.

L. rhinaria has been observed in man in the adult as well as in the larval condition (Pentastoma denticulatum). Zenker first called attention to the occurrence of the larva in man, having found it nine times in the liver in 168 autopsies. Heschl found it twice in Vienna in twenty autopsies, Virchow found it in Würzburg and Berlin, Wagner in Leipzig (10 per cent.), and Frerichs in Breslau five times in forty-seven autopsies. The parasite is much less frequent in Switzerland. According to Klebs, one case occurs in 900 autopsies, and according to Zaeslin two cases occurred in Basle to 1,914 autopsies. In the Seamen’s Hospital in Kronstadt P. denticulatum has been found six times in 659 autopsies. It was almost always the liver that contained one or a few specimens. The parasite was very rarely found in the kidney or spleen, or encysted in the intestinal wall. The adult L. rhinaria is far more rarely observed in man.

A case reported by Landon that related to a blacksmith of Elbing is particularly interesting. This man accompanied the campaign of 1870; he soon, however, fell ill with pains in the liver, accompanied by icterus and intestinal disorders. Soon after the war, and after the symptoms were reduced to icterus and weakness, bleeding of the nose set in and continued with slight intermissions for seven years; an unpleasant sensation of pressure in the left nasal cavity set in, with inflammatory swelling of the mucous membrane. At last, in the summer of 1878, when the pressure in the nose had considerably increased, a Linguatula was expelled from the nose with a violent attack of sneezing, and lived for three days longer in water. The bleeding of the nose then ceased and the patient soon recovered. There can be no doubt that the first illness was connected with the invasion in the liver of numerous larvæ of Pentastoma, and disappeared after their encystment; one or a few of these must subsequently have found its way to the nose and settled there.

Genus. *Porocephalus.*

*Porocephalus constrictus*, v. Siebold, 1852.

Syn.: Nematoideum hominis, Diesing, 1851; Pentastomum constrictum, v. Sieb., 1852; Porocephalus constrictus, Stiles, 1893.

Porocephalus is distinguished from Linguatula by its cylindrical body and by certain internal structures. Porocephalus constrictus is at present only known in its larval stage. It is milk white in colour with golden-yellow hooklets. Number of rings, twenty-three. Length 13 mm., breadth 2·2 mm. There are no prickles on the posterior border of the annulations of the body.

This species was first discovered by Pruner encysted in the livers of two negroes in Cairo. Bilharz reported two further cases in which the parasites were encysted in the liver and in the mucosa of the intestine; a few other observations have been made by Fenger, Aitken, Giard and Chalmas. Aitken’s report deals with soldiers of the British Colonies in Africa. The parasites were discovered in the liver as well as in the lung, and appear to have been the cause of death in one case (pneumonia, peritonitis).

Pruner has found the same parasite also in the liver of the giraffe.

It has recently been assumed that Porocephalus constrictus is the larva of Pentastoma moniliforme, Diesing, 1835, that attains a length of 70 mm. and lives in the lungs of African Pythonides. The larva is known to have been ejected from monkeys (Cercopithecus albogularis, Cynocephalus maimon), from the giraffe (Camelopardalis giraffa), from a species of hyæna (Proteles cristatus), and should be expected to occur frequently in smaller mammals which have been swallowed by African serpents of enormous size.

[The three species of Pentastomidæ, or tongue worms, found in man are Linguatula serrata, Frölich; Porocephalus armillatus, Wyman; and Pentastoma moniliformis, Diesing.

[(1) Linguatula serrata has been referred to under a great number of names.[356] It is a frequent parasite in dogs, oxen and sheep; as an adult in the dog and also in the fox and wolf. The nymphal stage is found in rats, hares, rabbits, the horse, oxen, sheep, goats, pigs, camels, deer, the African and long-eared hedgehogs, porcupine, guinea-pig and peccary. In man it is found in both adult and nymphal stages. Sambon says the nymphal stage is of frequent occurrence, but is usually overlooked. Zenker, who first found it in man, obtained it in nine out of 160 post-mortems, usually encysted in the liver. It is then said to be harmless. Landon, in 1878, found the adult in man, the patient suffering from epistaxis for about seven years; in the end during a fit of sneezing the living parasite was ejected through the nostril. This case is of particular interest as it appears to suggest that this Acarid may now and then pass its entire development in the same host, or at any rate may actively migrate from the liver to the nasal cavities after a period of encystment in the liver or elsewhere, which has also been observed in herbivorous animals (vide also p. 526).

[356] Synonymy given by Sambon: Adult form, Ténia lanceolé, Chabert, 1787; Ver rhinaire, Chabert, 1787; Tænia rhinaris, Pilger, 1805; Tænia lanceolata, Rudolphi, 1805; Cochlus rhinarius, Rudolphi, 1805; Prionoderma rhinaria, Rudolphi, 1808; Polystoma tænioides, Rudolphi, 1809; Linguatula tænioides, Lamark, 1816; Prionoderma lanceolata, Cuvier, 1817; Pentastoma tænioides, Rudolphi, 1819; Linguatula lanceolata, de Blainville, 1828; Linguatula rhinaris, Railliet, 1885; Linguatula caprina, R. Blanchard, 1900. Nymphal form: Linguatula serrata, Frölich, 1789; Tænia capræa, Abildgaard, 1789; Tænia caprina, Gmelin, 1800; Polystoma serrata, Goeze, 1800; Halysis caprina, Zeder, 1803; Linguatula denticulata, Rudolphi, 1805; Echinorhynchus capreæ, Braun, 1809; Tetragulus capriæ, Bosc, 1810; Pentastoma denticulatum, Rudolphi, 1819; Pentastoma emarginatum, Rudolphi, 1819; Pentastoma fera, Creplin, 1829; Linguatula ferox, Gros, 1849.

[It is recorded from man in Central America (Darling, Bull. Soc. Path. exot., 1912, v, p. 118; and again Arch. Int. Med., 1912, v, p. 401), also from Rio de Janeiro (Mem. Inst. Oswaldo Cruz, 1913, fasc. ii, p. 125) by Faria and Travassos.

[(2) Porocephalus armillatus, Wyman, is also known under a variety of names.[357] This species is widely spread over tropical Africa. The adult stage is found in pythons and puff-adders, the nymphal in the chimpanzee, Sykes monkey, mandrill and other monkeys, the lion, leopard, banded ichneumon, Aard wolf, dog, black rat, South African reedbuck and the giraffe. The adult has never been found in man or any mammal. No fewer than sixteen cases of the nymphal form, Sambon tells us, have been found in man, and it is probably much more widespread than at present known. So far it has only been found in the African natives. This species has sixteen to seventeen body rings in the male, eighteen to twenty-two in the female, and the body does not taper as much as in the next species.

[357] Adult form as Linguatula armillata, Wyman, 1847; Pentastomum polyzonum, Hailey, 1856; Pentastomum armillatum, Leuckart, 1860; Pentastomum armillatum, Diesing, 1864; Porocephalus armillatus, Stiles, 1893; Porocephalus polyzonus, Stiles, 1893; Porocephalus moniliformis, Neumann (in part), 1899. Nymphal form: Linguatula diesingii, van Beneden, 1849; Pentastomum euryzonum, Diesing, 1850; Nematoideum hominis, Diesing, 1851; Pentastomum constrictum, von Siebold, 1852; Linguatula constricta, Küchenmeister, 1855; Pentastoma leonis, Wedl., 1863; Pentastoma fornatum, Cobbold, 1879; Pentastomum protelis, Hoyle, 1883; Porocephalus constrictus, Stiles, 1893; Linguatula constrictor, Galli-Valerio, 1896; Pentastomum diesingii, Shipley, 1898.

[(3) Pentastoma moniliformis, Diesing,[358] is an Oriental species, found in India, Indo-China and South China, and the Malay Archipelago. The adult occurs in both the Indian and reticulated pythons. The nymphal stage has been found in monkeys, the tiger, the civet and the Indian otter.

[358] The synonymy is as follows:--Adult form: Pentastoma moniliforme, Diesing, 1835; Linguatule moniliforme, Mégnin, 1880; Porocephalus moniliformis, Stiles. Nymphal form: Pentastoma fornatum, Creplin (in part), 1849; Pentastoma wedlii, Cobbold, 1866; Pentastoma aonycis, Macalister, 1874; Porocephalus armillatus, Stiles (in part), 1908.

[The nymph has twice been found in man; in one case in the liver of a Filipino, the other in the serous coat of the small intestine of a native of Sumatra.

[This species can be told by the female having twenty-nine to thirty-three body rings, the male twenty-six, and the annulations are more bead-like and less prominent than in the African species.

[In addition to these three, Sambon thinks it probable that others occur in man.--F. V. T.]

OTHER REFERENCES TO Pentastomidæ.

(1) “Die Wanderung des Pentastomum denticulatum beim Rinde,” Centralbl. f. Bakt. u. Parasitenk., Jan. 2, 1889, v (1), pp. 1–5, V. Bates.

(2) “Il Pentastoma moniliforme, Dies., nella pantera,” Med.-vet. Torino, 1877, 4 s., vi (12), pp. 529–532, R. Bassi.

(3) “On the Organization and Development of Linguatula (Pentastoma), accompanied with the description of a new species from the abdominal cavity of the mandrill,” Ann. and Mag. Nat. Hist., 1848, 2 s. ii (7), 2, pp. 69–70, v. Beneden.

(4) “De la Linguatula ferox (Pentastoma denticulatum aut serratum),” Bull. Acad. roy. d. Sci. d. Belg., 1855, xxii, pt. 1 (1), pp. 4–10, v. Beneden.

(5) “Note sur quelques pentastomes,” Bull. Acad. roy. d. Sci. de Belg., 1857, 26, 2 s., ii (5), pp. 29–30, v. Beneden.

(6) “Ueber das Pentastoma in de gekrösdrusen den Schafe,” Repert. d. Thierh. Stuttg., 1861, xxii, pp. 37–38, Collin.

(7) “Eine Linguatula aus der Mesenterialdrüse des Schafes und Dromedars als zweites ungesche. Stadium von Pent. taenioides,” Notiz. u. Tagsber. u. d. Geb. d. Nat. u. Heilk. Jena, 1862, v, pp. 127, 128, Colin.

B. *INSECTA* (Hexapoda).

Three separate regions can always be distinguished in the body of insects, namely, the head, thorax and abdomen. The HEAD is a roundish unsegmented capsule and possesses four pairs of appendages. The first pair are the various shaped feelers (antennæ), which are placed on the superior surface of the head next to the eyes; then more ventrally placed a pair of upper jaws (mandibles) without palpi and without articulations; they are powerful masticatory organs.[359] The first pair of lower jaws (maxillæ) are jointed and bear a palpus (palpus maxillaris); the second pair of maxillæ are soldered together and form the lower lip (labium), and likewise carry a palpus labialis on each side. The upper lip (labrum), as well as the other parts (which, however, are only appendages), belong to the mouth, which is really formed of a number of closely united pieces. The mouth parts are modified according to the functions required of them. Coleoptera, Neuroptera, and Orthoptera have biting or masticatory mouth parts which conform with the scheme described above. In the licking mouth parts of the Hymenoptera the maxillæ and under lip are considerably elongated, while the mandibles retain their form and are used for triturating the food; in the Lepidoptera nearly all the mouth parts are shortened except the maxillæ, which form a long and sometimes spirally rolled suctorial proboscis; the Diptera and Rhynchota have piercing and sucking mouth parts. The mandibles and maxillæ are metamorphosed into needle-like structures, while the suctorial apparatus is formed by the labrum.

[359] [The mandibles are only powerful masticatory organs in biting-mouthed insects (Mandibulata); in the sucking or piercing-mouthed insects they may be absent, or in the form of needle-like stylets (Haustellata).--F. V. T.]

The thorax consists of three segments, which are frequently united; ventrally it carries three pairs of legs, which consist of a definite number of articulated pieces joined together. Their form also changes according to their function, so that legs for running, walking, digging, swimming, jumping, and preying are seen. A pair of wings are respectively attached to the last and last but one thoracic rings, and these may be traced back, not to metamorphosed appendages, but to tracheal branchia. They are composed of chitinous membranes supported by branched structures (veins or ribs). Their size and formation vary; they are seldom of equal size and form (Neuroptera); often the posterior wings are larger than the anterior wings, the former then only serving as protective coverings for the latter (Coleoptera), or the anterior wings are larger (Lepidoptera), or the posterior wings are shortened or are entirely absent (Diptera); and finally there are insects in which both pairs of wings are lacking.[360]

[360] [As in the order Aptera, which includes the Thysanura and Collembola, and also exceptions in other orders, as the fleas amongst Diptera, the Mutillus and ants amongst Hymenoptera.--F. V. T.]

The abdomen retains its segmentation, but, with the exception of a few groups related to the primitive forms of insects, has no appendages in the imago condition; the abdomen usually consists of ten segments, on the last of which the anus is situated.

We need only observe the following characters in considering the anatomy of insects:--

The EPIDERMIS consists of the chitinous cuticle, which is separate from the cellular layer beneath (hypodermis); the various appendages are supported by the chitinous layer.

The INTESTINAL CANAL usually consists of the anterior, median and terminal intestine, and as a rule passes straight through the body; salivary glands discharge into the anterior part, and, in some cases, yield a stiffening secretion which serves for spinning webs; numerous or scanty hepatic tubes are appended to the median intestine, while on the border between the median and terminal intestine open four to six long tubes (vasa malpighiana), which act as urinary organs. Finally the end portion of the intestine carries various glands (anal and rectal glands, etc.).

The CENTRAL NERVOUS SYSTEM agrees in structure with that of the Annelids, but is more highly developed. The pharyngeal ring surrounds the front part of the intestine; the sensory nerves originate from its SUPERIOR PHARYNGEAL GANGLIA and are the seat of the higher psychical functions; the INFERIOR PHARYNGEAL GANGLIA govern the mouth parts, and in addition appear to regulate the movements (cerebellum) of the vertebrates.

The chain of GANGLIA lying on the ventral side of the abdomen consists primitively of pairs of ganglia corresponding with the twelve segments, which are connected by longitudinal and transverse commissures. But many changes in the ganglia may be seen in insects caused by partial or entire amalgamation of single ganglia, so that in a few cases only one abdominal ganglion is present. In conclusion, a definite INTESTINAL NERVOUS SYSTEM is always present.

Of the organs of sense the FACETTED EYES, situated at the sides of the head, deserve special mention, as do also the ORGANS OF TOUCH and SMELL, situated on the antennæ, and the ORGANS OF HEARING and taste, or finer sensations, situated at the mouth and in the buccal cavity.

The sounds emitted by insects are, as a rule, produced by the friction or beating of certain chitinous parts, but sounds are also produced in breathing (flies).

The ORGANS OF RESPIRATION, the so-called tracheæ, are highly developed; there are openings (stigmata) at the sides of the body which draw in air by means of the active participation of the muscles of the body. The number of stigmata varies between two and ten pairs; the tracheæ themselves branch off from the trunks in the most varied manner, and carry air to the internal organs.

The colourless BLOOD circulates between the tissues and organs, and is kept circulating by the contraction of a chambered dorsal vessel provided with ostia, and which terminates in a short aorta opening at the anterior end.

Insects are SEXUALLY DISTINCT; their sexual glands are in pairs and have a tubular structure, but the testicular tubules are united together by a capsule into an oval testicle; exceptionally, also, the excretory canals are double, as also the sexual orifices; usually the paired canals unite into a single oviduct or spermatic duct which terminates at the posterior end of the body after receiving the products of various glands.

As to the HISTORY OF THE DEVELOPMENT of insects, all that is necessary to mention here is that the young hatched from eggs only exceptionally (as in Apterygota) resemble the adult parent (insecta ametabola); as a rule they differ from them not only in the shape of the body, but also more or less by their manner of life, and only attain the form of the parent through METAMORPHOSIS. This is a gradual process (insecta hemimetabola) in the Rhynchota and Orthoptera, or a sudden one with a stage of inanition (insecta metabola) in the other orders. This stage of rest or inanition, the PUPA, concludes the larval life (caterpillar, maggot, etc.); during the pupal stage no nourishment at all is taken, but the internal organs undergo changes; in some forms the rest is not absolute, as voluntary local movements may take place (pupæ of gnats).

The insects are divided into numerous orders according to the form of the mouth parts, the structure of the wings, as well as the manner of the development; with the exception of the lowest group (Apterygota), which is most nearly related to the ancestors of the insects, and which has no wings and undergoes no metamorphosis, all the remaining orders, which are termed Pterygota, have wings on the thorax, though there are, of course, a few species and families of this group which have lost their wings.

The Pterygota include--

(1) Orthoptera.--Biting mouth parts, anterior wings leathery, posterior wings thin, folded longitudinally; metamorphosis incomplete (grasshoppers, crickets, cockroaches).

(2) Pseudoneuroptera.--Biting mouth parts, wings of equal size, thin, not folded up (dragon-flies, hair and feather lice, termites).

(3) Rhynchota or Hemiptera.--Mouth parts formed for puncturing and sucking; wings alike, or the anterior wings may be thickened, parchment-like at their base (plant lice, cicadæ, bugs and true lice).

(4) Neuroptera.--Biting mouth parts; wings alike, thin; metamorphosis complete (ant-lions, lace-wing flies, etc.).

(5) Trichoptera.--Licking mouth parts; anterior wings narrow, posterior wings longitudinally folded, both ornamented with little hairs; the larvæ are worm-like in form, live in water, and breathe through tracheal gills (may flies, etc.).

(6) Lepidoptera.--Suctorial mouth parts; wings covered with scales (butterflies).

(7) Coleoptera.--Biting mouth parts; anterior wings thickened and differ in colour, appearance and function from the thin, folded posterior wings (beetles).

(8) Hymenoptera.--Mouth parts for licking and biting; the wings alike, membranous (ichneumon flies, ants, wasps, bees, humble bees).

(9) Diptera.--Mouth parts formed for puncturing, sucking or licking; posterior wings degenerated (gnats, flies, gadflies, fleas).

(10) Strepsiptera.--Anterior wings shortened; the female without wings and living parasitically (fan-wings).

The parasites of man occur amongst the Rhynchota, Coleoptera, and amongst the Diptera.

[The most usual and recent classification of the Hexapoda is the following:--

(1) Aptera.--Wingless insects; scarcely any metamorphosis.

(2) Neuroptera.--Four membranous wings, frequently with much network; the front pair not much, if at all, harder than the under pair; the latter with but little or no fan-like action in closing; mandibulate; metamorphosis variable, but rarely complete.

(3) Orthoptera.--Four wings; front pair coriaceous or leather-like, usually smaller than the other pair, which are of more delicate texture and contract in repose like a fan; mandibulate; metamorphosis complete.

(4) Thysanoptera.--Four very narrow fringed wings; mouth imperfectly suctorial; metamorphosis slight.

(5) Hemiptera.--Four wings; the front pair either all transparent or with the basal half leathery; mouth suctorial; metamorphosis slight.

(6) Diptera.--Two membranous wings only; mouth suctorial, very varied; metamorphosis complete.

(7) Lepidoptera.--Four large wings covered with scales; mouth suctorial, metamorphosis great.

(8) Hymenoptera.--Four membranous wings; front pair larger than hind, which do not fold up in repose; mandibulate, sometimes with a tubular proboscis; metamorphosis complete.

(9) Coleoptera.--Four wings, the front pair hard and horny (elytra), meeting in a line over the back and covering the delicate hind pair; mandibulate; metamorphosis complete.

[There are two other well-known arrangements, namely, Packard’s and Brauer’s, of recent date, but the one given here, which is based on Linnaeus’ grouping by Dr. Sharp, is by far the simplest.--F. V. T.]

Order. *Rhyncota.*[361]

[361] [Usually known as Hemiptera. There are two sub-orders, Heteroptera and Homoptera. The former have the base of the front wings coriaceous; the latter have all four wings membranous. The Homoptera are Aphides or plant lice and scale insects (Coccidæ), none of which attack man. Recently an interesting case has been reported to me where certain Aphides had been passed in human urine. One species was Rhopalosiphum dianthi, the other found in the urine was the hop aphis (Phorodon humuli). I cannot believe, however, that they had been actually passed, in spite of the case being reported by a medical man.--F. V. T.]

The lower lip forms a long thin tube that can be turned back (rostrum), and within which lie the setaceous mandibles and maxillæ; the first thoracic segment is not united with the two posterior ones; the anterior wings are usually leathery as far as the centre.

(a) RHYNCOTA APTERA PARASITICA.

Family. *Pediculidæ* (Lice).

The lower lip is transformed into a projecting rostrum provided with barbed hooklets in which the hollow extensile sucker (maxillæ and mandibles) is situated; no wings; no metamorphosis; only simple eyes; the antennæ are five-jointed, the feet possess hook-like terminal structures; the barrel-shaped eggs (nits) are deposited on the hair of the host.

[The lice or Pediculidæ are also known as Anoplura and Siphunculata.

[They have been split up into a number of families and sub-families and a number of genera, but as far as this work is concerned it is best to retain the single family Pediculidæ.

[Only the three species mentioned here are common parasites of man, but now and then horse and cattle and sheep lice, Hæmatopinus, may cause transitory annoyance.--F. V. T.]

Genus. *Pediculus*, Linnæus.

*Pediculus capitis*, de Geer, 1778.

Male 1 to 1·5 mm. in length, female 1·8 to 2·0 mm. in length. The colour varies from light grey to black according to the colour of the hair of the human race upon which they are parasitic. The abdomen has eight segments, of which the six central ones are each provided with a pair of stigmata. The thorax is as broad as the abdomen. Eggs 0·6 mm. in length; about fifty are deposited by a female head louse. The young can propagate when eighteen days old.

The head louse lives especially in the hairy parts of the head of human beings; more rarely it is found on other hairy parts of the body. It is spread over the entire surface of the globe, and was present in America before the arrival of Europeans. Quite exceptionally it is said that it bores itself deep into the epidermis and can live in ulcers.

[The eggs are pear-shaped and are attached to the hairs near the roots by means of a clasping collar. They hatch in about seven days. The young are like the adults and mature in a month. Its general colour varies with that of its host. In West Africans nearly black, in Hindoos dark and smoky, on Chinese and Japanese yellow, on Hottentots orange, on South American Indians dark brown (Murray).--F. V. T.]

*Pediculus vestimenti*, Nitzsch, 1818.

The head in front is somewhat rounded. Antennæ longer than in the head louse; 2 to 3·5 to 4 mm. in length; whitish-grey; the abdomen is broader than the thorax; stigmata as in P. capitis. Eggs 0·7 to 0·9 mm. in length; about seventy are deposited.

P. vestimenti lives on the neck, throat and trunk of persons, and the clothing next the body, in which also the eggs are deposited. The louse of so-called pedicular disease (P. tabescentium) is, according to Landois’ researches, only the usual P. vestimenti; moreover, many cases of phthiriasis are attributable to mites or fly maggots.

[This parasite has often been a great pest amongst soldiers during long campaigns, especially amongst the Russians during the Crimean War. Vide also notes in Addenda (p. 615) under “Body, Head and Clothes Lice.”--F. V. T.]

Genus. *Phthirius*, Leach.

*Phthirius inguinalis*, Redi, 1668.

Syn.: Pediculus pubis, L.

Male 0·8 to 1·0 mm. in length; female 1·12 mm. in length; colour greyish-white; form subquadrate; the two posterior pairs of legs are strong; the abdomen has nine segments and six pairs of stigmata; and still another pair of stigmata is situated between the two anterior limbs. Eggs pear-shaped, 0·8 to 0·9 mm. in length, 0·4 to 0·5 mm. in breadth, and are deposited in rows of about ten on the hairs.

Pediculus pubis, which is found almost exclusively in the Caucasian race, lives on hairy parts of the body, but hardly ever on the skin of the head; the pubic region is its favourite place of abode.

[This species reproduces more rapidly than other lice, and is communicated much more freely. The eggs are often laid singly attached to the hairs near their apex. It is known as the “crab louse.”--F. V. T.]

(b) RHYNCOTA HEMIPTERA.

Family. *Acanthiadæ.*

Body flattened, antennæ four-jointed, rostrum three-jointed, wings atrophied.

[This family, the Cimicidæ, includes the bed bugs; the proboscis, which lies in a groove, is of three segments; the front wings are shown by two small elytra, there is no trace of hind wings. Two species are known commonly to attack man.--F. V. T.]

Genus. *Cimex*, Linnæus.

*Cimex lectularius*, Linnæus.

Syn.: Acanthia lectularia, Fabricius, 1794.

It measures 4 to 5 mm. in length, 3 mm. in breadth; brownish-red; eight abdominal segments. The female deposits fifty whitish eggs at a time (1·12 mm. in length) three or four times a year; the entire development up to complete maturity takes about eleven months. [They will breed all the year round, but less so in cold weather.--F. V. T.]

The bed bugs live in the cracks and fissures of human habitations, under carpets, behind pictures, in furniture, bedsteads, etc.; hidden during the day, they attack persons at night to suck their blood. The alkaline secretion of the salivary glands dropped into the wound around the separate bites causes the so-called “wheals.”

The bed bugs were known in bygone days by the Greeks (κάριο) and the Romans (cimex). They were first mentioned from Strasburg in the eleventh century, and in England about 1500.

[This is the common bed bug of northern latitudes and must not be confused with the tropical bed bug (C. rotundatus). The bed bug can migrate from one house to another; this especially takes place when a house is uninhabited. They escape from windows and pass along walls, water-pipes and gutters, and so reach adjoining houses. This noxious pest accompanies man wherever he goes; ships and trains become infested, especially the former.

[A characteristic feature in this animal is the peculiar odour it produces, like many others in the same group of insects. This odour comes from a clear, oily volatile liquid secreted by glands in various parts of the body. Although the normal food is man’s blood, the bed bug can subsist upon moist wood, dust and dirt that collects in crevices in floors, walls, furniture, etc. The puncturing mouth consists of a fleshy under lip, within which lie four thread-like hard filaments which pierce the flesh, the blood being drawn up through the beak.

[The eggs are oval, white, with a projecting rim around one end, with a lid which is pushed off when the young hatch; they are laid in cracks and crevices in batches of from twelve to fifty. The egg stage lasts from seven to ten days. The larval stage so gradually passes into the adult that one scarcely notices the change; during its growth the skin is cast five times, and at the change the little wing-pads are seen, showing that the adult stage is reached. The young larva is at first pale yellowish-white. It resembles the parent, but has no trace of elytra. Although eleven weeks is said to be necessary for their development, the stages may be gone through much more rapidly; Howard and Marlatt[362] give seven weeks in some instances. It seems pretty certain that these Cimex only take one meal of blood between each moult and another preceding egg laying.--F. V. T.]

[362] “Household Insects,” Howard and Marlatt, Bull. 4 (N.S.), U.S. Dept. Agric., 1896, p. 37.

*Cimex rotundatus*, Signoret, 1852.

[This bug is common in warm climates; it is an abundant insect in India, and King has found it in the Sudan, where C. lectularius is, however, the common species. It is usually known as the tropical bed bug. Signoret’s bug can be told from the other common species by the shape of the pronotum. In C. rotundatus it is uniformly convex, whilst in C. lectularius the lateral edges are flat and sometimes even concave. The abdomen of rotundatus is also rather more elongate.

[This species is of considerable importance, as according to Patton it may act partly as the intermediary host of the piroplasma of kala-azar.

[Wenyon found at Bagdad that Cimex sp. would take up Leishmania from Oriental sore, and that the parasite developed into flagellate form. Patton came to the conclusion that the bed bug transmitted Oriental sore in Cambay, India, but Wenyon contests this view (vide Journ. Lond. School Trop. Med., 1912, ii, pt. 1, pp. 13–26). Franchini (Bull. Soc. Path, exot., 1912, v, No. 10, pp. 817–819) was unable to connect Cimex with this disease. At present nothing seems proved. Besides their possible connection with kala-azar, it has been shown by Howard and Clark (Journ. Exp. Med., 1912, xvi, No. 6, pp. 850–859) that they can carry the virus of poliomyelitis.

[This bed bug was originally described from the Island of Réunion in 1852 by Signoret. A similar insect was described from Burma by Fieber, in 1861, as C. macrocephalus. This is the same as Signoret’s species.

[The distribution given by Patton[363] is as follows: India, Burma, Assam, Malay, Aden, Islands of Mauritius and Réunion. Patton in this paper refers to an erroneous statement made in a recent edition of this book (the last English edition). As I have personally kept lectularius in moist dirt, wood and refuse for over two years, the statement as far as I am concerned is not erroneous. Moreover, since his doubting this fact the same experiment has been twice repeated with the same results. What they did and do persist on I cannot say.--F. V. T.] whilst collecting them. It is rounder and has shorter antennæ than

[363] Indian Med. Gaz., February, 1907, xlii, No. 2.

*Cimex columbarius*, Jenyns.

[This is common in parts of Europe in pigeon nests, and also amongst poultry (vide Report Econ. Zool. for year ending September 30, 1913, pp. 142–144, Theobald). It occurs in Britain on the latter and will attack man. I have personally been badly bitten C. lectularius. Jenyns also described a more pubescent species from swallows as C. hirundinis. I have recently received an account of the swallow bug invading a house in Kent and causing much annoyance.--F. V. T.]

*Cimex ciliatus*, Eversmann, 1841.

3·3 mm. in length, yellowish-red, thickly covered with hair; indigenous in Russia (Kasan).

[From a single specimen seen it is evidently distinct.--F. V. T.]

Family. *Reduviidæ.*

Head long, narrowed behind into a neck; eyes large, prominent; rostrum thick and curved; antennæ moderately long, slender at the tip; legs long and stiff; carnivorous.

Amongst the Reduviidæ one genus is of particular importance, namely the genus Conorhinus, which has a long head and the first segment of the beak very much shorter than the second, and the posterior tibiæ longer than the femora.

These large bugs have a wide distribution, the Oriental region, North and South America, and the West Indies, Madagascar and West and Central Africa.

These large bugs may cause very nasty wounds by their bites, but beyond that it has recently been shown that one interposes in the life-cycle of a trypanosome, namely--

Genus. *Conorhinus*, Lap.

*Conorhinus megistus*, Burm.

This large bug has recently been shown by Chagas to be the agent in the development of the trypanosome (T. cruzii) which is the cause of the well-known disease in many parts of Brazil called Barbeiro (Barbier). This insect is about 1 in. long, black, with four red spots on the pronotum, and six red lateral lines on the abdomen, black legs, head and beak. The insect is figured in a coloured plate (No. 9) in Mem. Inst. Oswaldo Cruz, 1909, i, fasc. 2, pp. 158–218.

A further account is given by Neiva.[364]

[364] Mem. Inst. Oswaldo Cruz, 1910, 2, fasc. 2, pp. 206–212.

*Conorhinus sanguisuga*, Lec. (Blood-sucking Cone-nose).

This bug is also known as the Texas or Mexican bed bug, also as the big bed bug. It is particularly troublesome in the Mississippi Valley in bedrooms. The bite is very severe and results in more pronounced swelling and inflammation than that of the Cimex. Normally this genus feeds upon the blood of mammals and insects. Its fondness for human blood appears to be quite a new habit, and appears limited to the mature insect only. It is nearly an inch long, flat, head very narrow and long, the rostrum short and thick. In colour it is dark brown with pink markings. They are fully winged when adult, and they fly with ease, entering houses on the wing, especially being attracted by lights in windows; they also run swiftly. Like the bed bug they conceal themselves during the day and come out at night and bite the sleeper. The effect of the bite is very varied, but as a rule a sore, itching wound, accompanied by burning pain and swellings, which may extend over a good deal of the body, occur. A specific poison is undoubtedly injected into the puncture; but no doubt serious results are also due to the beak being contaminated through the insects feeding upon foul carrion. Mr. Lembert, when bitten by a Conorhinus sp. (?) on the Pacific slope, exhibited the following symptoms: an itching sensation extending up the leg, large blotches manifesting themselves on the upper part of the limb and extending up to the hands and arms; his lips swelled and the itching and swelling extended over the head; there was also much nausea. Similar results are recorded from other regions.[365]

[365] “Household Insects,” p. 42.

The eggs of the C. sanguisuga are at first white, then become yellow, then pink; the young hatch in twenty days. There are two larval and two pupal stages, the latter showing wing-pads. The eggs are laid and the young feed out of doors, chiefly upon insects. It is particularly abundant in April and May indoors.

*Conorhinus*, sp. novum (Monster Bug).

Another species; acts in a very similar way in California, the bite being very poisonous.

*Conorhinus rubrofasciatus*, de Geer[366] (Malay Bug).

[366] [First Report Econ. Zool., 1903, p. 130.--F. V. T.]

This large bug attacks man in Malaysia and elsewhere. It is recorded as inflicting “a very nasty sting, which is done by the huge proboscis.” Acute pain and inflammation follow in a few minutes. In one case the whole leg became swollen. This species occurs over the whole Oriental region, in Madagascar and Sierra Leone. It is dark brown in colour with dusky yellow or brick-red markings on the pronotum and elytra. Donovan suggests that it may be connected with the kala-azar piroplasma.

*Conorhinus renggeri*, Herr-Schäff

(Great Black Bug of Pampas).

This large black bug is mentioned by Darwin,[367] who states as follows: “At night I experienced an attack (for it deserves no less a name) of the benchuca, a species of Reduvius, the great black bug of the Pampas. It is most disgusting to feel soft wingless insects, about an inch long, crawling over one’s body. Before sucking they are quite thin, but afterwards they become round and bloated with blood, and in this state are easily crushed. One which I caught at Iquique (for they are found in Chili and Peru) was very empty. When placed on a table, and though surrounded by people, if a finger was presented the bold insect would immediately protrude its sucker, make a charge and, if allowed, draw blood. No pain was caused by the wound. It was curious to watch its body during the action of sucking, as in less than ten minutes it changed from being flat as a wafer to a globular form. This one feast, for which the benchuca was indebted to one of the officers, kept it fat during four whole months, but after the first fortnight it was quite ready to have another suck.” Mr. Kirby[368] also refers to this species.

[367] Charles Darwin, “A Naturalist’s Voyage” (Voyage of the Beagle), 1888, p. 330.

[368] “Text-book of Entomology,” 1885, p. 205.

*Conorhinus variegatus* (Variegated Cone-nose).

Occurs in Florida in houses, and chases bugs (Cimex) and flies; not definitely known to bite man.

*Conorhinus nigrovarius.*

This species occurs in South America. It is one of the forms known as bichuque. Its bite makes a troublesome swelling.

*Conorhinus protractus.*

also attacks man in Utah.[369] It has been called the “big bed bug.”

[369] “The Big Bed Bug of the Far West,” Bull. 18 (N.S.), U.S. Dept. Agric., 1898, p. 101.

Genus. *Reduvius, etc.*

*Reduvius personatus*, Linné.

Syn.: Reduvius personatus, Leconte, 1855.

European, but also found in the United States. The bite causes intense pain. It bites when caught or handled, but does not seem to do so voluntarily. Swelling and irritation result which may last a week, and may even cause death.[370] In 1899 it was very abundant at Washington and elsewhere; other species occurred, and so no definite opinion existed as to the actual biter, but some people took R. personatus actually biting. It was first described as a parasite of man in America by Walsh and Riley.[371]

[370] “Insects to which the name ‘Kissing-bug’ became applied during the summer of 1899,” Bull. 22 (N.S.), U.S. Dept. Agric., 1900, p. 24.

[371] American Entomologist, 1869, i, pp. 84–88.

A popular name for this bug is the wheel or masked bug--a black insect, three-fourths of an inch long. The larva of this bug is carnivorous and covers its body with dust so as to conceal itself from its prey. The adult is active on the wing.

*Coriscus subcoleoptratus*, Kirby, 1837.

Syn.: Nabicula subcoleoptrata, Kirby, 1837; Nabis subcoleoptratus, Reuter, 1872; Coriscus subcoleoptratus, Stål, 1873.

Northern United States. Howard was bitten by one between the fingers--the pain was intense, like a needle prick, but the swelling was small.[372] No other case known.

[372] R. Blanchard, “Sur la Piqûre de quelques Hémiptères,” Arch, de Par., 1902, p. 145.

*Rasahus biguttatus*, Say, 1831.

Syn.: Pirates biguttatus, Stål, 1862; Callisphodrus biguttatus, Stål, 1866; Rasahus biguttatus, Stål, 1872.

Common in southern United States, and found in Cuba, Panama and Pará, etc. Known as the two-spotted corsair on account of the great spot on the hemielytra. Frequently found in houses, where it chases the bed bug. It also bites man frequently. From 1869 Walsh and Riley placed it amongst the parasites of man. In the United States Davidson[373] is of opinion that all cases attributed to spider bites are due to this insect.

[373] “So-called Spider-bites and their Treatment,” Therap. Gaz., February 19, 1875.

*Melanolestes morio*, Erichson, 1848 (Non-walker).

Syn.: Pirates morio, Erichson, 1848; Melanolestes morio, Stål, 1866; Pirates picipes, Herrich-Schäffer, 1848; Melanolestes picipes, Howard, 1900.

Guiana and Mexico and eastern and southern United States. Length 20 mm., hides under stones and logs during daylight, and flies at night. Attracted by lights into houses. Very abundant in 1899 at Washington. Howard cites cases where it was proved to bite man.

*Melanolestes abdominalis*, Herrich-Schäffer, 1848.

Syn.: Pirates abdominalis, Herrich-Schäffer; Melanolestes abdominalis, Uhler, 1875.

Allied to the former; some say similar, but can be told by the shorter wings on the female. It occurs in the same localities as M. morio.

*Phonergates bicoloripes.*

This reduvid attacks man in Africa.

Family. *Aradidæ.*

Broad and very flat bugs, with antennæ of four segments and the beak of three; scutellum short, no cuneus to elytra and the tarsi of two segments. They normally live under the bark of trees, etc., and are found in most parts of the world.

*Dysodius lunatus*, Fabr. (Pito Bug).

A large species which is found in South America, frequenting houses, and bites very severely.

THE OCHINDUNDU.

The bug is described by Wellman (Journ. Trop. Med., April 2, 1906, p. 97) as not only feeding on ticks, such as Ornithodorus moubata, but as also attacking man. It is called by the Angola Bantus the ochindundu. It is black in colour; the first two pairs of legs are of a bright red hue. It has curious paddle-like structures on the front four legs, which seem to be designed for securely holding the ticks. It infects native kraals for the sake of preying on ticks. The natives also state that it inflicts a bite which far exceeds in painfulness that of the tick. They compare the bite with that of a poisonous snake.

Family. *Lygæidæ.*

Scutellum short; antennæ four-jointed; ocelli present; membranous part of hemielytra with never more than five nervures. Nearly all vegetable feeders. A few are recorded here as biting man.

*Lyctocoris campestris*, Fabricius.

Syn.: Acanthia campestris, Fabr. (Lyctocoris domesticus).

Rare in habitations, lives on human blood. Found by Blanchard in a bed at an hotel at Liverpool. The bite is undoubtedly worse than that of Cimex; cosmopolitan. In colour it is ferruginous, shining, legs testaceous; hemielytra slightly shorter and narrower than the abdomen; membranous portion transparent, the apex broadly fuscous. Length 3·8 to 4·8 mm.

*Rhodinus prolixus*, Stål, 1859.

Sometimes attacks man, and the bite is very painful. It is 25 mm. long and 8 mm. broad, and occurs in Colombia. It is found also in Cayenne and Venezuela. This like other species is known in South America as bichuque or benchuca.

[A few other unimportant species are also recorded as biting man, such as Harpactor cruentas, in the South of France; Eulyes amœna, from Borneo and Java; Arilus carinatus, Forster, from Brazil. The latter appears to be the same as the Acanthia serratus, Fabricius.--F. V. T.]

Order. *Orthoptera.*

[The only Orthoptera recorded as doing actual harm to man are certain wingless locusts found in Africa. The cysticercus stage of a small tapeworm found in rats and man has been found in an earwig (Alcock).

[The strange Hemimeridæ found in West Africa, resembling wingless cockroaches, are parasitic on rats (Cricetomys). Phasmidæ, or stick insects, are said to be able to eject a fluid which may cause blindness if it comes in contact with the eyes.

LOCUSTS INJURIOUS TO MAN.

[A wingless locust--Enyaliopsis durandi, Luc--is recorded by Wiggins[374] as injurious to man in Uganda. “The bite of this insect,” it is said, “gives rise to a very nasty eruption, which may extend over the whole body, with high temperature and general malaise. The skin at the site of the bite sloughs away, and generally leaves a large deep cavity, which heals very slowly.”

[374] Bull. Ent. Res., 1910, i, pt. 3, p. 227.

[An allied species--E. petersi, Schaum--emits a clear yellow fluid, but according to Marshall this does no harm.[375] Stannus writes that “for some years I have been cognizant of the fact that among the natives of Nyasaland an allied if not the same species is held to cause skin lesions by the emission of a fluid on the bare skin surface of the body. I have seen cases of ulcers on various parts of the body, for which the ‘nantundua’ was assigned as the cause.” He then describes the destruction of the superficial layers of the skin which he observed after the yellow fluid had been on the skin twelve hours.--F. V. T.]

[375] Ibid., 1911, ii, pt. 2, p. 180.

Order. *Coleoptera.*

The larvæ of beetles, similarly to those of some other Arthropoda (myriapods and the larvæ of gnats), have sometimes been observed in man as purely accidental guests. In one case or another, such accounts may have originated through a mistake of the observer. Thus English doctors report the presence of the larvæ of Blaps mortisaga in the stools of human beings, Sandberg of the larva of Agrypnus murinus in his ten year old son, and Blanchard mentions the larva of a beetle that was vomited by a child. All these cases, however, do not represent actual parasitism, although there are beetles living parasitically.[376]

[376] [Dr. Daniels has sent me a small coleopterous larva found in an abscess on a man in British Guiana.--F. V. T.]

*Silvanus surinamensis*, Linnæus (Saw-toothed Grain Beetle).

[Taschenberg records this beetle as having invaded some sleeping apartments adjoining a brewery where stores were kept, and annoying the sleepers at night by nipping them when in their beds.

[This beetle is common in many parts of the world amongst groceries, corn, meal, seeds, dried fruits, etc. It is about 1/10 in. long, much flattened and chocolate-brown in colour. The thorax has two shallow grooves and bears six minute teeth on each side. The jaws are strong, but the bite cannot be very serious.--F. V. T.]

Order. *Diptera* or *Siphonaptera*.

*Aphaniptera* (Fleas).

Wingless, the thoracic rings distinct and free; antennæ of three segments; legs very powerful; abdomen with nine segments. [Ten segments are present, but only nine are visible.--F. V. T.] The mandibles transformed into serrated puncturing organs, which are situated in the split sheath of the rostrum; the maxillæ are laminated and have palpi, and more or less conceal the other parts.

The importance of fleas lies mainly in the fact that they act as plague carriers. About 150 species have already been described. The only ones of importance for this work are those found on man and those on rats and mice. The two families in which these are found are known as Pulicidæ and Sarcopsyllidæ.

The eggs of fleas are laid on the ground, on rugs, etc., and in birds’ and rodents’ nests. They hatch rapidly in warm weather and in warm climates, varying from two to five days; in cold countries they may take two or three weeks to incubate.

The larva is a footless creature, pearly white in colour, the head sometimes being darkened, composed of fourteen segments including the head, and although apodal can move with considerable agility. It lives amongst dust and dirt, and feeds upon any organic matter it can find. In about two weeks it is said to become mature, and then spins a cocoon in which pupation takes place.

The cocoons of the common human flea and the fowl flea become covered with dust and dirt. The period of pupal life seems varied, for I have had the fowl flea hatch out in ten days, and others in three weeks at the same time of year.

The adults are blood suckers and cause considerable irritation as well as acting as disease carriers, and in the Sarcopsyllidæ the females attach themselves permanently to their hosts, embedding themselves under the skin, where they become pregnant. Some kinds harbour the cystic stage of tapeworms, and the rat trypanosome passes certain stages in the rat flea. Most fleas have definite hosts, but some, like the rat and fowl fleas, attack man.

The fleas which can carry the bacillus of plague are Xenopsylla cheopis, Pulex irritans, Ceratophyllus fasciatus and Hoplopsyllus anomalus.

The two families, Pulicidæ and Sarcopsyllidæ, can be distinguished as follows:

Thoracic segments much foreshortened, coxæ and femora of hind legs very slightly enlarged Sarcopsyllidæ.

Thoracic segments normal, coxæ and femora of all the legs much enlarged Pulicidæ.

Family. *Sarcopsyllidæ* (Jiggers).

The members of this family are not confined to one host.

Three genera are known and tabulate as follows:--

α. Hind coxa without a patch of spines on the inside.

α^1. Hind femur simple 1. Dermatophilus. α^2. Hind femur with a large tooth-like projection near the base 2. Hectopsylla.

β. Hind coxa with a patch of short spines on the inside 3. Echidnophaga.

Genus. *Dermatophilus*, Guérin.

*Dermatophilus cæcata*, Enderl.

The eyes of the female vestigial. Taken on and behind the ears of Mus rattus in Brazil.

*Dermatophilus penetrans*, L., 1758 (Jigger, Chigoe).

Syn.: Sarcopsylla penetrans.

About 1 to 1·2 mm. in length; brown in colour. Eyes distinct. The males only occasionally visit man to bite; the fertilized female, on the other hand, bores into the skin with her head, particularly about the toes of the host, and then attains considerable dimensions. The eggs develop on the soil with a metamorphosis similar to that of the common flea.

The sand flea (nigua) particularly infests Central and South America, and, in 1873, was carried by ships from Brazil to the West Coast of Africa. In a comparatively short time it has become disseminated throughout Africa and has also appeared in Madagascar; recently also it has been reported from China.

Besides attacking man, it also settles on mammals, for instance, on dogs, pigs, etc. According to Jullien the wound or little swelling caused by the female has no particular significance, as children infested with ten or eleven sand fleas quietly proceeded with their games. It will be understood, however, that the wound easily affords the opportunity for the setting up of inflammation or even septic processes, as is the case in any kind of wound.

[The jigger is also well known in the West Indies.--F. V. T.]

Genus. *Echidnophaga*, Olliff.

Four species found on rats, etc.

*Echidnophaga gallinacea*, Westwood (Chigoe of Fowls).

[This flea is a native of tropical Asia and Africa. It lives on the fowl chiefly, attacking the neck and around the eyes. Specimens were sent me from Texas, where they not only attack poultry but also children, the latter somewhat severely. It also occurs on cats, and is found on rats in Africa. It has been introduced into North America.

[Three other species are found on rats, viz.: E. myrmecobii, Rothsch., from Australia; E. murina, Tirah, from Southern Europe; and E. liopus, Rothsch., India and Western Australia.--F. V. T.]

Family. *Pulicidæ* (True Fleas).

ROTHSCHILD’S CLASSIFICATION is as follows:--

SECTION I.--Club of antennæ distinctly segmented only on the hind side.

Key to Genera.

a. No comb on head and thorax.

a^1. The internal incrassation, which extends from the insertion of the mid coxa into the thorax, joins the anterior edge of the mesosternite Pulex.

b^1. This incrassation joins the upper edge of the mesosternite Xenopsylla.

b. With a comb on the pronotum only Hoplopsyllus.

c. With a comb on the pronotum and at the lower edge of the head Ctenocephalus.

SECTION II.--Club of antennæ distinctly segmented all round.

Key to Genera.

a. Eye developed.

a^1. No comb on head.

a^2. Pygidium not projecting backwards; frons with tubercle Ceratophyllus.

b^2. Pygidium strongly convex, projecting backwards; frons without tubercle Pygiopsylla.

b^1. Two spines at angle of genæ Chiastopsylla.

b. Eye vestigial or absent.

a^1. Abdomen without comb.

a^2. Hind edge of tibiæ with about eight short and several long bristles, which do not form a comb.

a^3. Fifth segment in fore and mid tarsi with five, and in hind tarsus with four bristles Neopsylla.

b^3. Fifth segment in fore and mid tarsi with four, and in hind tarsus with three lateral bristles, there being an additional pair of bristles in all the tarsi on the ventral surface in between the first pair Ctenophthalmus.

b^2. Hind edge of tibiæ with about twelve short and three long bristles, the short ones forming a kind of comb Ctenopsylla.

b^1. Abdomen with at least one comb Hystricopsylla.

Genus. *Pulex*, Linn.

*Pulex irritans*, L., 1758.

Male 2 to 2·5 mm. in length, females about 4 mm.; reddish or dark brown; head without bristles; thoracic and abdominal rings of bristles on the dorsal aspect, and small hairs directed backwards at the posterior margin. The barrel-shaped white eggs are deposited in cracks in the boards, sweepings, spittoons, etc.; they produce legless larvæ consisting of fourteen segments, which, after about eleven days, are transformed into pupæ; after another eleven days the flea emerges.

Fleas live in human dwellings all over the world, and periodically pass on to persons to suck their blood. They may deposit their eggs on very uncleanly individuals, and even undergo development, therefore it is possible to find larvæ and pupæ on such persons.

The dog flea, Pulex serraticeps, is easily distinguished from the flea of man by the large thick bristles on the posterior margin of the first thoracic ring (fig. 384).

Genus. *Xenopsylla*, Glink.

*Xenopsylla cheopis*, Rothschild.

This is the common rat flea of tropical countries. Rothschild[377] says: “Although practically cosmopolitan, it cannot apparently flourish in temperate and cold climates.”

[377] Bull. Ent. Res., 1911, i, pt. 2, p. 92.

In the male the bristles of the flap-like process of the clasper all slender; in the female the narrow portion of the receptaculum seminis long. Originally discovered in Egypt.

This is apparently the chief plague flea. The Indian Plague Committee have proved that this flea is easily infected when fed on plague rats, and that the bacillus multiplies rapidly in the flea’s stomach and that the fleas may remain infective for fifteen days. How the flea infects man does not apparently seem to have been proved, as it does not do so through its bite, but the excrement is highly infective. It is probable that this poisoned fæcal matter gets to the wound caused by the piercing mouth.

*Xenopsylla brasiliensis*, Baker,

occurs on rats in West Africa and has been introduced into Brazil.

Genus. *Ctenocephalus*, Kolen.

Includes the cat and dog fleas. The dog flea, C. canis, Dugès, is found on the dog all over the world, but especially in temperate climates. It also occurs on rats. Man is often badly bitten by this insect and it overruns houses. The eggs are laid on rugs, carpets and dust and dirt and amongst dogs’ hair, but are not fastened to it and fall anywhere. The ova may hatch in about fifty hours and the larvæ live for seven days and then spin their cocoons amongst dust and dirt. The pupal stage lasts about eight days.

The cat flea (C. felis) is widely distributed over the world, and occurs on many mammals beyond the cat, and is also found on rats.

Genus. *Hoplopsyllus*, Baker.

A genus found in North America related to Pulex, but at once recognized by the prothorax bearing a comb.

*Hoplopsyllus anomalus*, Baker,

which is found on the ground squirrel (Citellus beecheyi) in California, and according to Rothschild once found on the rat, has been proved to carry the plague bacillus and to play an important part in plague infection in California.[378]

[378] “Report United States Public Health, 1909,” xxiv, No. 29.

Genus. *Ceratophyllus*, Centis.

*Ceratophyllus fasciatus*, Bosc.

This flea is also found on the rat in Europe and will attack man. It is a plague carrier. It has eighteen to twenty teeth on the prothoracic comb and no black spines on the head. The genus Ceratophyllus of Centis has a pronotal comb and three ante-pygidial chætæ on each side. Two other specimens recorded: C. londiniensis, Rothsch., and C. anisus, Rothsch. The former on rats and mice in London, the latter on Felis sp. from Japan and Mus norvegicus in California.

Genus. *Ctenopsylla*, Kolen.

This genus contains a very abundant rat and mouse species, C. musculi, Dugès, which is widely distributed over the globe.

Genus. *Hystrichopsylla*, Tasch.

Large hairy fleas, with no eyes and one or more combs on the abdomen. In the Mediterranean area one species, H. tripectinata, Tirah, is common on rats and mice, and also in the Azores. Several others occur on rats and mice. For information concerning these the reader is referred to Rothschild’s papers.

*Pulex pallipes* is another species found on the rat and man.

*Systematic, Anatomical, and Biological Remarks on Mosquitoes.*

Mosquitoes come in the Nematocera, one of the sub-orders of the Diptera, and are divided into numerous families, of which, however, the Culicidæ are of most interest to us here. Other families as the Psychodidæ and Chironomidæ are also of considerable importance, vide following pages. The head is small, the facetted eyes are placed laterally, but there are no accessory eyes (ocelli). In front of the eyes are situated the comparatively long antennæ, the differences of which strongly mark the distinction of sex.[379]

[379] [This is by no means always the case; in the genera Deinocerites, Wyeomyia, Limatus, Theobald, and in Sabethes, Robineau Desvoidy, they are nearly the same in both sexes.--F. V. T.]

The antennæ are composed of fifteen or sixteen segments. In the male they are covered with long whorl-like hairs, while in the female the antennal hairs are short--differences that are perceptible even with the naked eye.[380] The proboscis, which is longer than the antennæ, protrudes from the inferior aspect of the head and is composed of the following parts (figs. 387 and 388): Two grooved half tubes, facing one another, of which the upper one is the upper lip (labrum) and the lower one the lower lip (labium), which represents a pair of coalesced maxillæ. Within the tube formed by the labrum and labium are the mandibles and maxillæ, transformed into instruments for piercing, and a single puncturing organ, the hypopharynx. On the right and left, next to the proboscis, are placed the straight five-jointed palpi, the final joint of which is thickened in the male.[381] In biting, the labrum, which is swollen at its free end, is not introduced into the wound like the other mouth parts, but is bent backwards. The labium and hypopharynx push direct into the skin; the maxillæ and mandibles, however, which are needle-like and serrated at the tips, penetrate with a saw-like movement. [The swollen free end of the labrum really means the labellæ, two articulated pieces, supposed by some to be the labial palpi. In most species the mandibles are not serrated at their ends.--F. V. T.] The saliva is introduced into the wound through the lumen of the hypopharynx, while the blood is sucked up by the mosquito in the groove of the labium.

[380] [This is not always the case, vide previous note.--F. V. T.]

[381] [This is only so in Anophelina and in the genus Theobaldinella, Neveu-Lemaire, Grabhamia, Theobald, Acartomyia, Theobald, etc. In true Culex and many other genera the male palpi are pointed.--F. V. T.]

The three thoracic segments are soldered together. The central one carries the membranous wings on the sides of the dorsal surface; the posterior somite carries the small halteres (rudimentary posterior wings). There are three pairs of long slender legs on the lower side.

† [This should read Anopheles maculipennis, Meig.; there was no type of A. claviger.--F. V. T.]

The abdomen has no limbs, is composed of eight (rarely nine) distinct segments; the sexual and anal orifices are at the posterior end, the stigmata on the sides. The intestinal canal (fig. 389) is composed of three principal divisions; the anterior part reaches as far as the front pair of legs, and consists of the œsophagus, which is provided with two small lateral diverticula. [At the commencement of the œsophagus are one or more diverticula, which vary in size; they contain air, food and bacteria.--F. V. T.] The mid gut reaches as far as the fifth and sixth abdominal ring; in front it is thin, and has numerous small supra-œsophageal ganglia; the posterior part is, however, more dilated. Four or five Malpighian tubes, the excretory organs, discharge at the place where the mid gut passes into the terminal gut.

The pair of salivary glands have one common excretory duct leading into the hypopharynx.

These glandular bodies are situated in the thorax; each consists of three slightly serpentine tubules, the dorsal and ventral tubes being long, the central one shorter. The above-named characteristics apply to both genera Culex and Anopheles, but in the genus Culex is smaller, Anopheles larger. [In Anopheles the ends of the ducts in the lobules are dilated, whilst in most of the genera the ducts are the same size all along. The lobules may bifurcate, and in Psorophora there are five lobules.--F. V. T.] The legs of the genus Culex are about the same length as the whole body; in Anopheles they are double that length.[382] In Anopheles the palpi and proboscis are of equal length; in Culex the condition is different, according to sex. In the male the palpi are longer than the proboscis; in the female considerably shorter and the number of segments diminished. The venation of the wings exhibits further points of differentiation, as also their adornment, though this last sign is not by any means always conclusive; most species of the genus Culex have unspotted wings, whilst those of Anopheles are usually spotted. More important is the fact that in Culex the abdomen is decorated with small scales, similar to those on butterflies, whereas there are small bristles on the abdomen of Anopheles. [This cannot be said to be a character by which an Anopheline may be told from a Culicine, for in such common Anopheline genera as Cellia and Neocellia we get plenty of scales on the abdomen.--F. V. T.] An experienced observer can, however, separate the two genera by the difference in size and their manner of resting. When settled they either touch the resting place with all the legs or only with the four anterior legs. In consequence of the different length of the legs, the body of Culex approaches the resting place more closely; moreover, Culex holds the abdomen parallel or at an acute angle to the resting surface, whereas Anopheles carries the abdomen directed upwards (at an angle of about 145°) and holds the head down. Both genera, however, usually only rest on the four anterior legs, and then, as has long been known, Culex carries the third pair directed towards the dorsum, while those of Anopheles hang down.

[382] [This is certainly not always the case.--F. V. T.]

In regard to the differentiation of the species, I must refer you to the special literature, and content myself by observing that about 150 species of Culex and about fifty species of Anopheles have been described, of which fifty about four are found in Europe. [The number of known Anophelines now is more--100 species--of other Culicidæ over 700.--F. V. T.] According to our present knowledge it appears that the entire genus Anopheles can transmit malaria to man; this observation has been confirmed in Anopheles claviger, Fabr.; A. maculipennis, Meig.; A. bifurcatus, L.; A. superpictus, Grassi; A. pseudopictus, Gr., all of which are found in Italy,[383] Germany, etc., as well as in the tropics. Moreover, in A. costalis, Loew; A. funestus, Giles (Africa); A. quadrimaculatus, Say (North America), and A. rossii, Giles; the latter is perhaps identical with A. superpictus, Gr., as well as with A. culicifacies (India). [Anopheles maculipennis and A. claviger are the same. Certainly neither maculipennis nor bifurcatus has been found in the tropics. Anopheles quadrimaculatus, Say, is the same as A. maculipennis. There is no evidence that all Anophelines carry malaria, but there is much to show that certain species only are capable of so doing. A list of known carriers is given later.--F. V. T.]

[383] Compare Ficalbi, E., “Venti spec. di zanzare (Culicidæ) ital...,” Bull. Soc. ent. ital., 1899, xxxi; abstracted in Centralbl. f. Bakt., Par. u. Infektionsk., 1900, xxviii, p. 397.

Everyone is aware that mosquitoes swarm at sunset in fine weather, and then seek out human beings and other warm-blooded animals to take food. In this regard, however, the sexes differ, for it is almost without exception that the females only suck blood, while the males subsist on the juices of plants (blossoms or fruits).[384] After sucking, and when night has fallen, the mosquitoes find a place of refuge, for which purpose they utilize the grasses or foliage of trees and bushes, or inhabited or uninhabited rooms of houses, also cellars, stables, verandahs, etc., where they also pass the day.

[384] Both males and females may be kept alive in captivity for a long time if given fruits, or even only sugar and water.

[Some mosquitoes bite in the daytime--Stegoymia and some Anophelines; some bite right into the night, as Culex fatigans and C. pipiens.--F. V. T.]

The period required for digestion varies according to the temperature. It takes two days in summer, and may take up to ten days or more in cool weather. After digestion is complete more food is taken up, this being necessary [in some species only--F. V. T.] for the maturing of the sexual products in the female.

It is still unknown under what circumstances copulation takes place;[385] in any case, sooner or later the females are fecundated, and when the ova have become mature, and the season is not too far advanced, they seek a suitable place in which to deposit them.[386] These are larger or smaller, permanent or temporary, collections of standing water, pools, puddles, lakes, pits, water in rain-water barrels, basins, etc. Nevertheless, certain kinds prefer certain waters; thus Anopheles (claviger) maculipennis and several of the Culices seek stagnant water overgrown with swamp vegetation and decomposing vegetable matter; A. bifurcatus and certain Culices, clear water with some vegetation (such as fountains and the lakes in gardens and parks); Culex pipiens has a preference for rain-water barrels, even though the water be dirty and evil-smelling. [I have found the larvæ of Anopheles bifurcatus living in great numbers in ponds and lakes completely overgrown with floating water-weeds, and those of Culex pipiens in liquid manure.

[385] The act of copulation in many species is now known. The female Culex has three receptaculæ seminalis, while the female Anopheles has one receptaculum seminis.

[386] It is certain that the females perish immediately after depositing the ova; but this does not always hold good, as a part of them survive for a few days. The males die soon after copulation.

Sexual Organs of the Mosquito.--The female has a pair of ovaries, opening into a single tube by the ovarian tubes; into the single tube opens a duct coming from the spermathecæ, and also a mucous gland. The spermathecæ store up the male cells. The male organs consist of two testes joined by ducts (vasa deferentia) to the ejaculatory duct formed by their union. Each vas deferens is joined by a short tube with the sac-like vesicula seminalis.--F. V. T.]

There is also a difference in the manner in which Culex and Anopheles deposit their ova. Culex deposits two to three hundred eggs in compact heaps that float on the water, and in which the eggs stand perpendicularly one next the other; whereas Anopheles maculipennis deposits only three or four up to twenty eggs, united in groups that float horizontally on the water; the eggs of A. bifurcatus, again, are arranged in star-like groups. The eggs are about 0·75 mm. in length, and assume a dark hue soon after being laid. The development only occupies a few days. The young larvæ grow rapidly, changing their integument several times; the larvæ also differ in the various genera, though they have a general resemblance (figs. 391 and 392).

The long legless larva has a flattened head, a fairly broad, rectangular, or trapeziform thorax, on which there are bristles, and an abdomen distinctly segmented, and on the segments of which there are also lateral bristles. The situation of the stigmata marks the difference between the two genera. Though in both genera the stigmata are at the posterior end and on the dorsal surface, they are in Anopheles close to the surface of the body; in Culex, however, they are on the free end of a long tube (siphon).

The position of the larva in the water also differs. The larva of Anopheles lies almost horizontally beneath the surface of the water, the posterior border of the penultimate abdominal segment, upon which the stigmata are situated, being on the surface; whereas the larva of Culex hangs head downwards perpendicularly in the water, the point of the siphon only touching the surface.

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