Chapter IX (part 2 of 2)

Chapter IX (part 2 of 2)

The Echinoidea are sharply divided into three main orders, which differ from each other profoundly in their habits and structure. These are: (1) The ENDOCYCLICA or Regular Urchins, of which the species just described may be taken as the type. (2) The CLYPEASTROIDEA or Cake-urchins, which are of extremely flattened form, and in which the periproct is shifted from the apical pole so that it is no longer surrounded by the genital plates, while some of the tube-feet of the dorsal surface are flattened so as to serve as gills. (3) The SPATANGOIDEA or Heart-urchins, in which the outline is oval: the periproct is shifted, as in the Cake-urchins, and the dorsal tube-feet are similarly modified; but the Heart-urchins have totally lost Aristotle's lantern, whilst the Cake-urchins have retained it. This strongly-marked cleavage of the group was primarily due, as in all such cases, to the adoption of different habits by different members of the same group. Were we to term the three orders Rock-urchins, Sand-urchins, and Burrowing-urchins, it would not be entirely true, for secondary invasions of the other's territory on {530}the part of each order have undoubtedly taken place; but still the statement would remain roughly true, and would give a fair idea of the differences in habitat which have led to the differentiation of the group.

ORDER I. ENDOCYCLICA (Regular Urchins).

The principal variations concern (1) the peristome, (2) the periproct, (3) the corona, (4) Aristotle's lantern and its appendages, (5) the spines, (6) the pedicellariae, and lastly, (7) the tube-feet. We shall consider these points in order.

PERISTOME.—In the vast majority of species this region is covered only with flexible skin in which ten small plates are embedded, pierced by pores for the buccal tube-feet; besides these there are irregularly arranged thin plates. In the Cidaridae both the ambulacral and the interambulacral series of plates are continued on it; these plates differ from those of the corona in being movable on one another. In Echinothuriidae only the ambulacral series of plates is continued on to the peristome. In the case of both these families there are a considerable number of tube-feet within the region of the peristome which may be classed as buccal.

PERIPROCT.—This area, which represents the whole dorsal surface of Asteroidea, is very large in the Cidaridae, where, as in Echinus, it is covered with leathery skin in which small plates are embedded. In the Saleniidae it is covered with a single large sur-anal plate, in the edge of which the anus is excavated; in the Arbaciidae it is covered with four valve-like plates; whilst in the remaining species its condition is similar to that described in the case of Echinus esculentus.

CORONA.—In Echinothuriidae all the plates are separated by slips of membranous skin, so that the test is flexible. In all other families it is an unyielding cuirass. In the Cidaridae the pore-plates remain separate throughout life, and are therefore identical with the ambulacral plates. These are small and placed in two vertical rows, and so the ambulacra are exceedingly narrow. In Echinothuriidae there is some tendency to adhesion amongst the pore-plates; these are of different sizes, and usually one larger and one smaller adhere to one another. In all other species regular ambulacral plates are formed at least {531}in the lower part of the radii near the peristome by the adhesion of the pore-plates in groups of two, three, or more. Sometimes as many as nine pore-plates may thus adhere.

When adhesion takes place between the pore-plates it is of course preceded by crowding, and this interferes with their equal development. Some which extend so far horizontally as to meet their fellows of the opposite side of the radius are called primary plates; others which are small and wedged in between the larger ones are called demi-plates. Systems of classification have been built up (chiefly by palaeontologists) in which great stress has been laid on how the primaries and secondaries enter into the constitution of the compound plate, but it does not seem to the present author as if this were at all a satisfactory basis for classification. All the pore-plates are primarily equivalent, and the question as to which are interfered with in their growth so as to become secondary is trivial. The so-called Arbacioid type consists of one primary with a secondary on each side; the Diadematoid type of three primaries, with occasionally a secondary between the aboral and the middle primary; and finally the Triplechinoid type of two primaries, with one or more secondaries between them.

ARISTOTLE'S LANTERN.—Under this head we may consider the auriculae and gills as well as the jaws and teeth. In Cidaridae external gills appear to be absent, but from the lantern coelom large radial pouches project upwards into the general coelom cavity. These pouches are supposed to be respiratory, and are termed INTERNAL GILLS or STEWART'S ORGANS.[488] They co-exist with external gills in Echinothuriidae and in Diadematidae, though in the last family they are present only in a vestigial form, two being found in each radius. The auricular arch both in Cidaridae and in Arbaciidae is composed of two pillars which do not meet, but in the last-named family they are based, as in Echinidae, generally on the ambulacral plates, whereas in Cidaridae they arise from the interambulacral plates (the ambulacral plates being here very narrow). The epiphyses are absent in Cidaridae and Arbaciidae, and are imperfect in Diadematidae.

SPINES.—These organs are extraordinarily variable, and {532}usually differ very much in species of the same genus. In the vast majority of species there is a limited number of long spines called "primaries," amongst the bases of which a large number of much shorter "secondaries" are distributed. In Cidaridae the primaries are very long and thick and blunt at the ends, and the secondaries form small circles around their bases. The primaries in Cidaridae and the tips of the primaries in Arbaciidae and Echinothuriidae are covered with a special investment of extremely close, hard, calcareous matter very different from the loosely fenestrated material out of which the bodies of the spines of all species are composed. In Colobocentrotus and Heterocentrotus the primaries are very thick and triangular in section, whilst the secondaries on the aboral surface have expanded outer ends, which form a close-set pavement protecting the ectoderm from the shocks of the breakers. In Echinothuriidae the primaries are short and so delicate as to be termed silky.

PEDICELLARIAE.—In Cidaridae only gemmiform and tridactyle pedicellariae are found. In the gemmiform the glands lie inside the grooved blades instead of outside as normally, and they are covered internally by ingrowths of calcareous matter from the edges. In Echinothuriidae only tridactyle and trifoliate are found in most species, but rudimentary gemmiform are found in one species and well-developed ophicephalous in another. In some species (Centrostephanus longispinosus) there are found gemmiform pedicellariae which have lost the jaws but retained the glands. These are termed "globiferae." Mortensen[489] uses minute details in the structure of the pedicellariae to discriminate species and even genera, but in this the present author is not prepared to follow him.

TUBE-FEET.—The tube-feet belonging to the aboral surface are pointed and devoid of a sucker in Diadematidae, Echinothuriidae, Arbaciidae, and Cidaridae;[490] in the last-named family those belonging to the oral surface have suckers, in the centre of which a pointed (sensory) prominence is to be noted.

The CLASSIFICATION of the Endocyclica is by no means in a satisfactory condition, and different authorities have arrived at {533}widely different results. Agassiz,[491] for instance, places the genera Echinus (the common British form) and Strongylocentrotus (the commonest American form) in different families. Bell,[492] on the other hand, considers them to be closely allied. Bell's system, based as it is on the development of the peristome, seems to the present author the most justifiable, for the peristome is undoubtedly a differentiation of the corona, which has been brought about by the manner in which the animal breathes and masticates, two functions of prime importance. The periproct is also of importance, representing as it does the whole aboral surface of the Starfish, and so are to a less extent the arrangements of the spines and of the tube-feet. Proceeding in this way, living Endocyclica can be divided into six families, which are briefly described below.

FAM. 1. CIDARIDAE.—Endocyclica with a large peristome and a large periproct. The peristome is covered with a regular series of both ambulacral and interambulacral plates, the former pierced by tube-feet. No special buccal tube-feet and no external gills. The periproct is large, and is covered with irregular plates (Fig. 236, A). The lantern coelom is provided with large Stewart's organs.

{534}The auriculae are incomplete and consist only of pillars arising from the interambulacral plates. The ambulacral pore-plates remain disunited, and the pores are arranged in a single vertical series; hence the ambulacra are very narrow. The interambulacral plates each bear one large primary spine surrounded by several circles of secondaries. No ophicephalous or trifoliate pedicellariae are to be found, and the gland of the gemmiform pedicellaria is placed inside the concavity of the blade.

The Cidaridae are in many respects the most primitive of the six families living. They are distributed all over the world, and chiefly inhabit deep water. No two naturalists agree as to how they are to be divided into genera. Mortensen,[493] who takes the structure of the pedicellariae as his principal guide, recognises fourteen genera. Others (as for instance Bell) have been inclined to attribute nearly all the living species to one polymorphic genus, Cidaris, finding all attempts to divide the genera from one another frustrated by the discovery of transitional forms. Goniocidaris (Fig. 237), however, distinguished by its comparatively broad poriferous zones, by bare places in the middle line of both radii and interradii, and by deep pits on the lines of suture of the plates, is by general consent distinct. This genus is confined to the Eastern Pacific, but from British waters three species of Cidaris have been recorded, only one of which, C. (Dorocidaris) papillata, is at all common. It is found in water from 100 to 500 fathoms in depth {535}off the western coast of Ireland and Scotland. It also occurs in the Mediterranean, and has been carefully examined and described when living by Prouho.[494] From his description it appears that locomotion is effected almost entirely by spines, and that the tube-feet of the lower parts of the radii have each in the centre of the disc a pointed sense-organ like those in the centre of the first tube-feet of the just metamorphosed Echinus, whilst those of the aboral surface have no suckers.

FAM. 2. ECHINOTHURIIDAE.—Endocyclica with a large peristome and comparatively small periproct. The peristome has a regular series of ambulacral plates bearing pores for tube-feet, but no interambulacral plates. No specially modified buccal tube-feet, but external gills are present, and internal gills (Stewart's organs) also occur. The periproct is covered with numerous small plates. All the plates of the corona are separated by thin slips of flexible body wall. Numerous comparatively short primary spines on both ambulacral and interambulacral plates; these spines are covered on the tips with a layer of hard dense material.

{536}[Illustration: FIG. 238.—Oral view of Asthenosoma hystrix. × ⅔. (From Wyville Thomson.)]

This remarkable family is divided by Mortensen into ten genera, based as usual on the pedicellariae, but taking into account also the shape of the tip of hard material on the spines. Most authors refer the majority of the species to two genera, Phormosoma and Asthenosoma (Fig. 238), recognising also a genus Sperosoma for one or two aberrant species. Asthenosoma is distinguished by having wide interspaces of membrane between the plates, and by having ten longitudinal folds of the body-wall, two in each radius, in which powerful longitudinal muscles are developed projecting inwards in the radii. The organs of Stewart are very large. In Phormosoma, on the contrary, the interspaces of membrane are very narrow, and the longitudinal folds are thin and membranous and the organs of Stewart are vestigial. Asthenosoma hystrix and Phormosoma placenta have both been dredged in deep water off the Irish coast. A. urens, in which there are ectodermic poison-sacs at the bases of the spines, inhabits the Indian Ocean near Ceylon, and was thoroughly {537}described by the Sarasins,[495] who regarded its structure as a proof that Echinoidea were derived from Holothuroidea. Both palaeontology and embryology have, however, yielded strong evidence that Echinoidea were derived from Asteroidea, and hence there is ground for believing that Holothuroidea are descended from primitive Echinoidea and not vice versa. The Echinothuriidae may perhaps be regarded as showing the first steps in the change, and though possibly not closely related to the actual ancestors of the Holothuroidea, they at any rate show parallel modifications.

FAM. 3. SALENIIDAE.—Endocyclica with a large peristome and periproct. The peristome is covered with thin, scattered, irregular plates. There are five pairs of special buccal tube-feet, each supported by a special plate, and there are external gills. The periproct is excavated in the side of a large central pentagonal plate. It is covered with fifteen or twenty plates.[496] The ambulacral plates are separate as in the Cidaridae, but occasionally adhere in pairs near the peristome. The interambulacral plates also, as in Cidaridae, each bear one large primary spine surrounded by a {538}circle of secondaries. A few deep-water forms belong to this family, the type genus Salenia (Fig. 240) being the best known. None occur in the British area. Superficially they resemble the Cidaridae, but in reality they are widely separated by the essentially modern character of the peristome.

FAM. 4. ARBACIIDAE.—Endocyclica with a peristome on which, as in Saleniidae, there are only ten prominent plates perforated by the buccal tube-feet, and besides these thin irregular plates; external gills are present, and the auricles consist of incomplete arches springing from the ambulacral plates. The periproct is covered by four valve-like plates. The ambulacral pore-plates are separate near the periproct, but near the peristome unite on the "Arbacioid" pattern (v. p. 531) to form secondary plates. The interambulacral plates each carry several spines. No representatives of this remarkable family are known in British waters, but Arbacia is found both on the east coast of North America and in the Mediterranean. It is distinguished by its conical test. All the upper tube-feet are devoid of a sucker; only those on the oral surface are used for locomotion.

Uexküll has studied the Mediterranean species, and has shown that the spines converge no matter how strong the stimulus may be, and so are incapable of aiding in locomotion; also that the ectoderm is devoid of ciliation, and hence the faecal matter which falls on the surface of the animal is not, as in other genera, allowed to fall off by the divergence of the spines nor swept off by the action of the cilia. In its natural habitat the wash of the ripples on the shore cleanses the animal. In captivity it is liable to suffocate itself.

FAM. 5. DIADEMATIDAE.—Endocyclica with a peristome similar to that of the Arbaciidae and the Saleniidae. External gills present and ten buccal tube-feet. Periproct small, covered with numerous small plates. The auricles form complete arches arising from the ambulacral region. Aristotle's lantern is provided with rudimentary Stewart's organs. The ambulacral pore-plates are separated at the apex, but unite orally in {539}"Diadematoid" fashion (p. 531) to form compound plates. The interambulacral plates bear numerous primaries. The aboral tube-feet are pointed, having lost their suckers.

This family is represented (according to Agassiz) at the present day by seven genera, none of which are found in British waters, though one (Centrostephanus) enters the Mediterranean. C. longispinus[497] was investigated by Uexküll and found to be distinguished by its sensitiveness to light and shade, and by the quickness of its movements, which were mainly carried out by its long spines. The family resembles the Arbaciidae in the pointed aboral tube-feet, but in the complete auriculae it resembles the next family.

FAM. 6. ECHINIDAE.—Endocyclica with peristome and periproct as in the preceding family. External gills and buccal tube-feet present, but Stewart's organs totally absent. Ambulacral plates combined on the "Triplechinoid" plan (p. 531) to form secondary plates. Interambulacral plates with numerous tubercles. All the tube-feet have suckers.

This family contains by far the larger number of living genera. It is divided into two sub-families, viz.:—

(a) TEMNOPLEURINAE.—Echinidae in which the plates of the corona dovetail into each other by means of pits and knobs along the line of suture. This sub-family does not occur in British waters; almost all the species are confined to the Indian and Pacific Oceans, but on the east coast of America it is represented by several genera, which however inhabit deep water, e.g. Trigonocidaris arbacina.

(b) ECHININAE.—Echinidae in which the plates meet each other in straight, simple sutures.

This sub-family is represented in British waters by three genera, viz. Echinus, Sphaerechinus, and Strongylocentrotus. Echinus is distinguished by having its pores arranged in arcs of three, owing to the fact that its pore-plates are united in threes to form secondary plates, whilst in the other two genera the ambulacral plates are composed of four or more pore-plates. Six species of Echinus have been recorded from British waters, viz. E. esculentus, E. acutus, E. miliaris, E. norvegicus, E. microstoma, and E. elegans. The validity of the last three is very doubtful. {540}Mortensen[498] regards E. norvegicus and E. microstoma as mere variations of E. acutus, and this is probably correct. E. esculentus has already been described; its most marked character is the forest of comparatively short, close-packed, reddish or white primary spines with which it is covered, between the bases of which the delicate secondaries are hard to detect. It is essentially a shallow-water species. E. acutus is distinguished by having much fewer and longer primaries and numerous delicate secondaries. It is an inhabitant of deeper water, being abundant at 100 fathoms, though stragglers are found in shallower water. At the depths at which it lives wave-disturbance can scarcely be felt, and hence the long primaries are not irritated.

E. elegans has spines intermediate in character between those of E. esculentus and those of E. acutus. Like the latter it is an inhabitant of the deeper water. It seems to the present author not at all improbable that further research might show that E. acutus, E. elegans, and E. esculentus are all members of continuous series of forms; certainly the larvae and early development of E. acutus and E. esculentus, the extreme members of the series, are strikingly similar.

E. miliaris differs somewhat widely from the other species and is closely allied to E. microtuberculatus of the Mediterranean, from which it is distinguished mainly by the greater thickness of the scattered plates on the peristome of the latter species. From the other British species it differs in its much smaller size and in the greenish hue of its primary spines, which are short and thick and possess purple tips. Its larva is markedly distinct from the larva of E. esculentus. E. miliaris is a littoral species, and is found in great numbers in some of the Scottish sea-lochs; when the tide recedes, under every stone of the gravelly beach several specimens will be found. It has a curious habit of "dressing" itself, i.e. of covering itself with fragments of dead shell, sea-weed, etc., which are held in position by the aboral tube-feet. This habit aids in concealing the animal, and has probably been developed on account of the dangers to which E. miliaris is exposed owing to its littoral habit of life.

Sphaerechinus differs from Echinus in the structure of the ambulacral plates, in which it agrees with Strongylocentrotus, but it is distinguished from this genus by the very deep {541}gill-clefts, or indentations of the edge of the corona from which the gills are extruded. Its most marked peculiarity, however, as shown by both Mortensen and Uexküll, consists in the highly developed character of its gemmiform pedicellariae, on the stalks of which are situated glands. When the head with its poison-glands is torn off, the secretion of these stalk-glands can envelop an enemy with a glutinous secretion, which impedes its movements. The blades on a slight mechanical stimulus divaricate very widely and become locked in this position, so that the enemy's body gets in well within their reach. The muscles of the poison-glands contract, but their ducts are bent by the act of opening, so that the secretion cannot escape. The sense-organs have stiff hairs, which penetrate the surface of the enemy and cause its juices to exude and so stimulate the blades to close, and at the same time permit the poison to be expelled. It will be remembered that the gemmiform pedicellariae of Echinus open in response to a chemical stimulus and close on a mechanical one being superadded; so that their responses are the direct opposite of what occurs in Sphaerechinus. S. granularis, a Mediterranean species with short red spines, just reaches the Channel Islands.

Strongylocentrotus has shallow gill-clefts and gemmiform pedicellariae, like those of Echinus, except that they have a muscular stalk. In the British area it is represented by two species, S. lividus, in which the primary spines are markedly longer than the secondaries and are of a brownish purple colour, and S. droëbachiensis, in which the primaries are little longer than the secondaries and are of a greenish brown colour. S. lividus occurs abundantly in the Mediterranean, and reaches the English Channel and the west coast of Ireland. In the last-named locality, where it is exposed to the full sweep of the Atlantic, it is said to excavate holes for itself in the limestone rocks, about ten inches in depth.[499] S. droëbachiensis, which has been recorded in the British area, chiefly from the west coast of Scotland, is one of the most abundant members of the fauna of the east coast of America. In the Gulf of St. Lawrence and in the branches of the Bay of Fundy it is found in thousands, and {542}is frequently left bare at low tide. It thus takes the place of E. miliaris in the British fauna. An allied if not identical species, S. purpuratus, is found in Puget Sound on the Pacific coast.

Other interesting genera of the Echininae are Echinometra, Colobocentrotus, and Heterocentrotus. All possess large, thick primaries, and all are elliptical in outline. In Echinometra the primaries are pointed, and the long axis of the body makes an oblique angle with the axis passing through mouth and madreporite. In Colobocentrotus and Heterocentrotus the axis passing through mouth and madreporite is the short axis of the ellipse, and the primary spines are very thick and triangular in section, whilst the expanded ends of the secondaries form a closely set armour between the bases of these. In Colobocentrotus the test is markedly flattened on the under side, and this flattened area is fringed with a circle of primaries; but in Heterocentrotus there are a few rows of primaries all over the test. These are tropical genera and are found on the outer side of coral reefs, and they require the cuirass of expanded secondaries to protect them against the waves.

ORDER II. CLYPEASTROIDEA (Cake-urchins).

The "Cake-urchins" have only one representative in the British area, and this is unsuitable for dissection on account of its small size. We shall therefore select as type the "Sand-dollar" Echinarachnius parma (Figs. 241, 242), which occurs abundantly in shallow water on the east coast of North America. As its popular name implies, this is an extremely flattened Sea-urchin of nearly circular outline, so as to suggest a resemblance to the silver dollar of North American currency. The peristome is exceedingly small, and is placed in the centre of the lower surface (Fig. 241), whilst the periproct is placed on one edge. The outline is not quite circular, for the periproct lies in a slight indentation of the edge; and this side is broader and of a lesser degree of curvature than the opposite one, so that a secondary bilateral symmetry is superimposed on the fundamental radial symmetry common to all Echinoderms. A line drawn so as to pass through the anus and the centre of the disc will divide the animal into two similar halves; the periproct of course lies in {543}an interradius and the axis of symmetry passes through the centre of one radius. We can thus distinguish an anterior group of three radii, or "trivium," from a posterior pair or "bivium." The madreporite lies in the left anterior interradius. The five genitals and five oculars surround a dorso-central plate, which covers the spot which in Endocyclica is occupied by the periproct.

The whole test is covered with extremely short delicate spines, which form a velvety felt-work, and are all of approximately the same length; they are of a brownish purple colour. The spines on the dorsal surface are all ciliated, and these cilia cause a current of fresh sea-water to flow continually over the modified tube-feet. Pedicellariae are scattered amongst the bases of the {544}spines; they are of the tridactyle, the gemmiform, and the ophicephalous types, but they have only two jaws.

The ambulacral areas on the upper surface of the test can be distinguished only by the flattened respiratory tube-feet (Fig. 242, pod'), which can be seen protruding from between the spines. Below these areas are clearly marked, for in the centre of each is a well-marked groove proceeding inwards to the peristome. This groove receives lateral branches on its course which traverse the adjacent interambulacral regions. The purpose of these grooves will be explained later. The interambulacral regions do not reach the peristome, which is entirely surrounded by the ambulacral areas. The ambulacral and interambulacral areas both consist of somewhat large hexagonal plates, except in the region of the respiratory tube-feet. Here the pore-plates are not united with one another. This region in each radius is termed {545}a "petal" (Fig. 243, A, p), for the respiratory tube-feet are arranged in two rows which diverge from their commencement at the "calyx" and slightly converge again towards the outer margin of the disc, and thus in a dried specimen the two rows of double pores outline an area having some resemblance in shape to the petal of a flower. Besides these double pores for the larger tube-feet there are numerous small single pores for the smaller tube-feet; these are found in all the plates, ambulacral and interambulacral, of the dorsal surface, but in the neighbourhood of the grooves only on the ventral side.

The sphaeridia are only present to the number of one in each radius. Each sphaeridium is enclosed in a pit situated near the edge of the peristome.

A remarkable feature in the skeleton of Echinarachnius which is characteristic in greater or lesser degree of all Clypeastroidea is the presence of vertical partitions of calcareous matter traversing the coelom and stretching from the upper to the lower surface of the test. These are found principally in the peripheral region of the animal; and there can be no doubt that they have originated as cellular bands traversing the coelom, for the formation of similar structures can be followed step by step in the Crinoidea. In the axis of these trabeculae, or folds of the coelomic wall, jelly is secreted, and into this the lime-producing {546}amoebocytes wander. In Echinarachnius these partitions are arranged in groups, each group radiating from a common centre.

The main peculiarities in the structure of Echinarachnius are comprehensible when the species is viewed from above in its normal environment. It is found in comparatively shallow water on a sandy bottom, and normally is nearly but not quite buried in the sand. It might thus be overturned by the force of the waves and currents, and it is protected against this fate by its flattened shape. This shape, however, necessitates some kind of support for the upper part of the test, and this is provided by the internal partitions.

In order to view the internal anatomy of the "Sand-dollar," it is necessary carefully to pick away the dorsal surface of the shell piece by piece. In this way the whole course of the alimentary canal is exposed; as in Echinus esculentus it can be seen to issue from the upper surface of Aristotle's lantern. It then bends sharply to the left, and makes a complete circle round the edge of the disc; this portion is the stomach, and is considerably inflated and accompanied by a "siphon." It then bends sharply back on itself, but only goes half way round; when it reaches the posterior interradius it ends in the anus (Fig. 244).

Aristotle's lantern is greatly simplified as compared with its condition in the Regular Urchins. Both rotulae and compasses are absent; the jaws are sharply bent on themselves, and their appearance gives one the impression that they have shared in the process of compression which the test as a whole has undergone, and have thus become bent. The teeth are nearly horizontal, and they actually articulate with the auriculae, which, as in Cidaridae, consist of disconnected pillars and spring from the plates of the interradius. Each pillar is fused with the adjacent one belonging to the next radius, so that the system which in Echinus consists of five radial arches here consists of five interradial pillars. Aristotle's lantern has lost its respiratory function and apparently its masticatory function as well, for the teeth are used as spades to shovel into the mouth the sand mixed with organic detritus and small organisms on which the animal lives.

The water-vascular system is highly modified. There are two sharply marked kinds of tube-feet—(a) the respiratory tube-feet, (b) the locomotor tube-feet. Both kinds are terminated by {547}suckers, but the first variety are much larger than the second; they possess a flattened lobed base, and are connected with the ampulla by a double canal. They issue only from the double pores which form the petal. The locomotor tube-feet are small and cylindrical; they are, as already mentioned, scattered over the whole upper surface of the test, penetrating both ambulacral and interambulacral plates, but all are connected by transverse canals with the radial canals of the water-vascular system. On the under surface they are confined to the neighbourhood of the ambulacral grooves, which have nothing to do with the ambulacral grooves of an Asteroid, but are due to secondary localisations of the tube-feet, which are here also connected in each radius with a single radial canal. The appearance of a living Echinarachnius covered with a veritable forest of short brown tube-feet is very striking.[500]

The condition of the water-vascular system is to be explained entirely by the peculiar environment of the animal. The demand for specialised respiratory organs is brought about by the habit of living half buried in the sand. Under these circumstances the strain of supplying the needful oxygen is thrown on the {548}dorsal tube-feet, and they become modified in order to fit them for this function. The locomotor tube-feet are very small and feeble compared with those of Echinus esculentus, but this is comprehensible when it is recollected how little resistance the yielding sand would offer to the pull of a powerful tube-foot like that of the Regular Urchins, for in order to move the creature through the sand a multitude of feeble pulls distributed all over its surface is necessary, and the locomotor tube-feet are exactly fitted, both as to size and number, for this object.

The principal points in which Clypeastroidea vary amongst themselves are (1) the nature of the internal skeleton, (2) the shape, and (3) the spines.

INTERNAL SKELETON.—In Echinocyamus and its allies this consists in each interradius of two simple partitions radiating out towards the edge of the disc; in Laganum it consists of walls parallel to the edge of the disc; in Clypeaster, of isolated pillars.

SHAPE.—In Echinocyamus the outline is oval and the test comparatively high. In Clypeaster and its allies the outline is pentagonal, and the test is swollen up into a blunt elevation in the centre. In a large number of genera, however, the test is, as in Echinarachnius, extremely thin and flat, and the outline may be variously indented. A first indication of this process is seen in Echinarachnius itself, but in Rotula the edge is drawn out into finger-like processes which are all interradial. In Mellita these processes unite with one another distally so as to surround spaces called "lunules," which appear as perforations of the test.

The CLASSIFICATION of the Clypeastroidea adopted by Agassiz is based chiefly on the degree of development of the internal skeleton, and as this is of great physiological importance to the animals we shall follow it here; but since it was published the remarkable discovery has been made of Pygastrides, a type previously known only from fossils. We must therefore recognise two sub-orders:—

SUB-ORDER I. PROTOCLYPEASTROIDEA.

Anus on dorsal surface near apical pole. One species, Pygastrides relictus,[501] with no "petals," from deep water in the Caribbean Sea.

{549}SUB-ORDER II. EUCLYPEASTROIDEA.

Anus on under surface.

FAM. 1. FIBULARIDAE.—The "petals" are short and imperfect, and the internal skeleton consists of two short outwardly-directed septa in each interradius. To this family the only British Clypeastroid, Echinocyamus pusillus, belongs. This animal never exceeds an inch in length, and has an oval outline. It inhabits shallow water, and is often found in the same ground as Echinus miliaris, but like all Clypeastroids it prefers a sandy bottom.

FAM. 2. ECHINANTHIDAE or CLYPEASTRIDAE.—"Petals" well marked, internal skeleton consisting of isolated pillars. The largest Cake-urchins belong to this family, which is found chiefly in tropical waters. Clypeaster, the great Cake-urchin, with a deeply sunken peristome, belongs to this family.

FAM. 3. LAGANIDAE.—Closely allied to the foregoing, but distinguished by the fact that the internal skeleton consists of walls parallel to the edge of the test. (Laganum, Arachnoides, Peronella.)

FAM. 4. SCUTELLIDAE.—This family includes about half the genera, and is sharply distinguished from all the rest by (1) the extremely flattened shape, (2) the indentation of the outline in the anal interradius and often elsewhere, (3) the branching of ambulacral furrows on the under surface. Echinarachnius, taken as the type in describing the anatomy of the Cake-urchins, is the best-known genus. Others are Mellita, with five perforations in the edge of the test; and Rotula, with the edge produced into a number of finger-like processes.

ORDER III. SPATANGOIDEA (Heart-urchins).

As the type we may select Echinocardium cordatum, which occurs abundantly in the Clyde and on the west coast of Ireland. The animal is found buried in sand at a depth of about 8-10 inches from the surface. At this depth it lies in a burrow, the walls of which are kept from collapsing by the somewhat broadened tips to the spines. This burrow communicates with the surface by a narrow cylindrical opening similar to the opening of the burrows made by the Clams and other bivalves. A little practice, however, enables one to distinguish the burrow of the Heart-urchin from these.

{550}The animal is about the size of a small potato, and is of light straw colour. Its outline is oval, and the test is about two-thirds as high as the shorter diameter. It is thus higher in proportion to its width than is the case with any living Cake-urchin. The highest point is behind the centre. The narrower end of the animal terminates in a vertical edge, in the upper part of which is a large periproct covered with a number of thin movable plates. The mouth is situated on the under surface, considerably nearer the front end of the test than the hinder end. It is entirely devoid of jaws or of teeth, and also of gills or of a movable peristome.

Aristotle's lantern has entirely disappeared, leaving as the only trace of its former presence a canal with membranous walls encircling the mouth, which has the form of a transverse slit, the posterior lip projecting considerably forward.

The ambulacral areas are easily distinguishable from the interambulacral areas by being comparatively bare of spines. On the upper surface they are distinctly grooved, the groove being especially deep in the case of the anterior one. On the lower surface they coalesce round the mouth, shutting out the interambulacral regions, and are here perforated by the large pores of the buccal tube-feet. Between the two posterior radii on the oral surface there is a space with specially arranged spines called the plastron or sternum. The interambulacral plates composing this region are very much lengthened, and interdigitate with one another at the sutures. To this lengthening is due the apparent forward shift of the mouth. The spines are very characteristic, and are very different from any which have as yet been described. They are the sole organs of locomotion. The primaries are long and curved, with flattened tips, admirably adapted to plough through the sand in which the animal lives. On the upper surface, mingled with the tube-feet, are a large number of small secondary spines. Between the two posterior petals there is a hoop-shaped band of very small black spines. These spines are ciliated, and draw a current of fresh sea-water over the respiratory tube-feet. Beneath the periproct there is a similar band called the "sub-anal fasciole"; this probably produces a current of water which sweeps away the material ejected from the anus.

The pedicellariae are of the trifoliate and gemmiform varieties. {551}The sphaeridia are situated in open pits, one or two in each, situated at the bases of the tube-feet nearest the mouth.

When the upper part of the test is picked away, the course of the alimentary canal is exposed (Fig. 247). It is very similar to the alimentary canal of Echinarachnius, except that from the first coil a large blind pouch, called the caecum, is given off.

The water-vascular system shows many characteristic features. The tube-feet are confined to two rows in each ambulacrum, the scattered smaller feet found in such abundance in Echinarachnius being entirely absent. There are four distinct varieties of tube-feet in Echinocardium, which are as follows:—(a) The respiratory tube-feet of the petals. These have, as in Echinarachnius, broad flat bases, but they have lost the sucker. (b) The prehensile tube-feet of the anterior ambulacrum. These are enormously long structures, measuring when expanded several times the length of the body. They end in discs, which are frayed out into fingers, so as to look like miniature sea-anemones. These tube-feet are comparatively few in number and are confined to the apical portion of the anterior ambulacrum. (c) The buccal tube-feet. These are short, thick, and pointed, and covered with a multitude of club-shaped processes. They are found on all the ambulacra in the neighbourhood of the mouth. (d) The degenerate tube-feet found in the portions of the ambulacra between the "floscelle" (see p. 553) and the petals. These are single and pointed, few in number, and issue from single pores in the test.

This extraordinary diversity in the tube-feet is fully explained {552}when the habits of the animal are known. The function of the respiratory tube-feet requires, of course, no special elucidation, but the peculiar anterior ambulacrum was a mystery till the feeding habits of the animal were observed by the late Dr. Robertson[502] of Cumbrae. He found that the animal protruded the long prehensile tube-feet through the opening of the burrow up to the surface of the sand. With their finger-like processes they then collected the surface film of the sand, which was impregnated with Diatoms and other small organisms. When a "handful," so to speak, of this nutritive material has been collected, the long tube-foot is withdrawn down the burrow and passed over the deeply grooved part of the ambulacrum to the buccal tube-feet, to which the food is given up. These last then push it into the mouth. Only one prehensile tube-foot is extended at a time.

The stone-canal is very short and soon opens into the axial sinus; it is widely separated from the pore-canals which traverse the madreporite. Communication between the two is effected by the long axial sinus. There are only four genital organs.

Heart-urchins vary amongst themselves chiefly in the {553}following points, viz.:—(1) the shape and position of the peristome, (2) the characters of the "petals," and (3) the number and position of the fascioles.

PERISTOME.—In many genera this is pentagonal and central, and in these cases the interradii commence at the peristome with a single plate, which is often covered with a thick crowd of small spines and is termed a "bourrelet." The oral ends of the radii also often consist of a crowded series of narrow plates, looking something like a "petal," and termed a "phyllode." The five bourrelets and five phyllodes constitute a flower-like figure termed a "floscelle."

AMBULACRA.—In Echinoneus all five are alike and are provided with similar tube-feet, which are respiratory but possess suckers. The ambulacra are not grooved, and the petaloid arrangement of the pores is hardly marked; but in Cassidulus, Pourtalesia, and many other genera the five petals are well marked, though they are all similar to one another.

FASCIOLES.—These structures are often entirely absent; the sub-anal one alone is present in Spatangus. In Eupatagus a peripetalous one is added. This surrounds all the "petals," and has obviously the function of sweeping fresh water over the respiratory tube-feet. In Echinocardium, as we have seen, there is an "internal fasciole" between the two anterior petals which has a similar function. In addition, this genus possesses an anal fasciole which surrounds the anus and sweeps away the faeces.

The CLASSIFICATION of the Spatangoidea is based mainly on the degree of development of the petals, that is to say, on the extent to which the burrowing habit has been developed. But weight is also laid on the shape of the peristome, the pentagonal form being more primitive. Seven families are recognised, which are as follows:—

FAM. 1. ECHINONIDAE.—"Petals" hardly marked at all; peristome in the centre of the lower surface and pentagonal. Floscelle not developed.

One genus, Echinoneus (Fig. 248).

{554}FAM. 2. NUCLEOLIDAE.—"Petals" distinct; peristome as in the foregoing family. No floscelle. Nucleolites, with the anus in a furrow. Anochanus, with a concave apical system serving as brood-pouch.

FAM. 3. CASSIDULIDAE.—"Petals" usually distinct; peristome eccentric, but provided with a well-marked floscelle.

Echinolampas, with the anus on the under surface.

Neolampas, with the anus on a projecting papilla. One specimen of this genus has been dredged in the British area.

The three foregoing families probably use their tube-feet to walk with, and bury themselves only to a slight extent. They are often united as a sub-order, the ASTERNATA, and distinguished from all the rest which possess an eccentric mouth and well-marked plastron. These families are then grouped together as STERNATA. They are as follows:—

FAM. 4. ANANCHYTIDAE.[503]—Spatangoidea with elongated apical system, ambulacra all similar and not grooved. Petals feebly marked. Pourtalesia, with bottle-shaped posterior prolongation of the test. Platybrissus, with flattened test.

FAM. 5. PALAEOSTOMATIDAE.—An aberrant family consisting of one genus, Palaeostoma. Petals grooved, with a peripetalous fasciole, but peristome central and pentagonal.

{555}[Illustration: FIG. 250.—Hemiaster philippi. × 2. (From Wyville Thomson.)]

FAM. 6. SPATANGIDAE.—Spatangoidea of more or less flattened shape, with well-marked petals and a sub-anal plastron as well as the ventral one. One fascicle at least, but a peripetalous one never present. The anterior ambulacrum grooved and different from the rest. This family is represented in British waters by two genera, Spatangus and Echinocardium. The former possesses only a sub-anal fasciole, and has specially long curved spines on the ventral plastron. It is represented by two species, S. purpureus and S. raschi, the latter being distinguished by a pointed lower lip. It is a deep-water species, found in 100 fathoms and over on the west coast. S. purpureus is fairly common in rather shallow water. From observations made on specimens kept in confinement it appears to burrow only so far as to leave the petals uncovered; hence there is no need of a peripetalous fasciole. Echinocardium is devoid of the thicker spines on the plastron, and has an internal fasciole and a perianal one as well as the sub-anal. As already mentioned, it is a deep burrower. It is represented by three species, E. cordatum, E. pennatifidum, and E. flavescens. The first, described as the type of the Spatangoidea, has a deeply grooved anterior ambulacrum. In the remaining two species this ambulacrum is not grooved. E. flavescens has only six or seven pairs of pores in the posterior {556}petals, E. pennatifidum twelve to fourteen. Both come from deeper water than E. cordatum.

FAM. 7. BRISSIDAE.—Allied to the Spatangidae, but distinguished by sunken petals and a peripetalous fasciole.

Two genera are recorded from the British area, Schizaster and Brissopsis, but the first has only been found once in deep water; the second is common. Schizaster has the front petals three times as long as the hind ones, and no sub-anal fasciole. Brissopsis has the front and hind petals of about the same length, and a sub-anal fasciole. The only British species is called B. lyrifera, on account of the fiddle-shaped outline of the peripetalous fasciole.

Hemiaster (Fig. 250) in general resembles Schizaster, but the petals are equal in length, and the two posterior serve as brood-pouches for the young. This genus is mainly Antarctic.

FOSSIL ECHINOIDEA.—Echinoidea are well represented in the geological record, and form a characteristic element in many fossil faunas. They appear in the Ordovician formation, but the first representatives of an existing family (Cidaridae) only appear in the Permian.

Space will only permit us to treat of the extinct members of the group very briefly. Leaving out of sight the representatives of families still living, the fossil Echinoidea may be divided into two great groups, viz.:—

(a) Palaeozoic forms, which in some points serve to connect the Endocyclica with the primitive Asteroidea.

(b) Mesozoic forms, which serve to connect the Clypeastroidea and Spatangoidea with the Endocyclica.

{557}[Illustration: FIG. 252.—A, Bothriocidaris. × 1. B, Palaeoechinus. × 1. amb, Ambulacral plates; inter, interambulacral plates. (After Zittel.)]

The Palaeozoic forms are often called Palaeoechinoidea, and they are above all distinguished by the fact that the number of vertical bands of plates composing the corona is variable, in a word, that the corona has not yet acquired a fixed definite constitution. One genus (Echinocystites) has the anus outside the apical system. It has four rows of pore-plates in each radius, and numerous rows of plates each with a single spine in the interradii. Another (Palaeodiscus) has been shown by Sollas[504] to be in many respects the missing link between Asteroidea and Echinoidea. Inside the plates of the corona there is a series of ambulacral plates like those of Asteroidea. The tube-feet in the oral portion of the radii seem to have issued between the (outer) ambulacral plates. No anus has been detected. All the rest are Endocyclic. The oldest known form, Bothriocidaris (Fig. 252, A), from the Ordovician, has only one row of interambulacral plates and two of ambulacral; no peristome is distinguishable from the corona. The ARCHAEOCIDARIDAE appear in the Devonian. They have narrow ambulacra of two rows of pore-plates as in the Cidaridae, but the interambulacra consist of many rows, the members of which overlap, and therefore were probably slightly movable, as in the Echinothuriidae; the primary tubercles are large, and there is only one on each plate. The MELONITIDAE (Fig. 252, B) appear in the Carboniferous. Each interambulacral plate, of which there may be five rows in each interradius, bears numerous small tubercles, and there may be four or more vertical rows of pore-plates, though in the genus figured, Palaeoechinus, there are only two. The TIARECHINIDAE are represented by one genus, Tiarechinus, with an enormous apical system, from the Triassic of the Tyrol. The interambulacra consist of one plate bordering the mouth, three, {558}side by side, forming the interradial area of the corona, and one large genital plate; the ambulacra, of two rows of pore-plates. This family consists of dwarfed forms which probably inhabited the land-locked seas and salt lagoons of the Triassic epoch.

When we recollect that some of the oldest Asteroidea known to us had very narrow arms and interradial areas edged by large square marginals, it does not require a very great effort to imagine how these marginals could be converted into the vertical rows of the interambulacra, and the pointed narrow arms becoming recurved, could have formed the ambulacra. The physiological advantage of this will be discussed in the chapter on development.

True Cidaridae occur in the Permian, and are abundant in all the younger formations. One Cretaceous genus, Tetracidaris, has four rows of interambulacral plates near the mouth, diminishing to two at the apex. This circumstance renders it probable that the Cidaridae are the direct descendants of the Archaeocidaridae. The Saleniidae, Echinothuriidae, and Diadematidae appear in the Jurassic, the Echinidae in the Cretaceous, and the Arbaciidae only in the Tertiary epoch.

Turning now to the Mesozoic forms with an excentric anus, there were a number of forms which have been grouped together as HOLECTYPOIDEA which had auricles and teeth and gills, although these were only feebly developed, and in which the pore-plates remained separate. The periproct was a comparatively large area, and in Pygaster, as in the surviving form Pygastrides, it was in contact with the apical system, although outside it. Many of the genera were of considerable height in proportion to their length. In Conoclypeus and Discoidea the jaws and auricles were very weak. The ECHINOCONIDAE have only vestigial auricles, and on this account are often definitely grouped with the Spatangoidea, but they are closely allied to the Holectypoidea. They are Cretaceous forms of high conical shape (Galerites). In Hyboclypus (Fig. 253) all trace of the teeth has disappeared, {559}but the periproct is large and in contact with the apical system; these forms appeared in the Jurassic. The COLLYRITIDAE, also Jurassic, had a marginal anus. The apical system was so much elongated that two of the ocular plates are widely separated from the other three, two opposite interambulacra meeting between them. Unmistakable Spatangoidea (Spatangidae and Ananchytidae) appear in the Cretaceous, true Clypeastroidea (Fibularites) in the Cretaceous, the other families in the Tertiary.

Reviewing these facts, we see that from the Holectypoidea we can pass by insensible steps on the one hand into true Clypeastroidea, and on the other hand into true Spatangoidea. The Holectypoidea differed from Endocyclica only in the position of the anus, and the initial step in the backward shift of this organ is seen in Pygaster. One result follows from this conclusion, that the modification of the dorsal tube-feet into breathing organs, and the consequent appearance of petals which accompany the taking on of burrowing habits, were independently developed in the Clypeastroidea and Spatangoidea, since these features were absent in the more primitive members of both groups.

{560}CHAPTER XIX

ECHINODERMATA (CONTINUED): HOLOTHUROIDEA = SEA-CUCUMBERS

CLASS IV. HOLOTHUROIDEA

This class of the Eleutherozoa comprises those sausage-shaped, leathery Echinodermata familiarly known as Sea-cucumbers. They are named Holothuroidea from ὁλοθούριον, an animal described by Aristotle, and believed to belong to this class.

The Holothuroidea resemble Echinoidea in the fact that the radial canals of the water-vascular system run backwards and upwards from the ring-canal over the surface of the body, terminating in small papillae near the anus, which, as in the Echinoidea Endocyclica, is situated at the upper pole of the body. There are, of course, no arms; and a further resemblance to Echinoidea is shown by the fact that the ambulacral grooves are represented by closed epineural canals, and that the ectoderm consists of long, slender, flagellated cells interspersed with gland-cells, underneath which is a plexus consisting of nerve-fibres and small bi-polar ganglion cells. There are, however, no spines or pedicellariae; and Holothuroidea differ not only from Echinoidea, but from all other Echinodermata, in the vestigial character of their skeleton, which consists merely of isolated nodules of calcium carbonate embedded in the skin. The body-wall is provided with transverse muscles running across the interradii, and also with powerful longitudinal muscles, running along the radii, by means of which worm-like contractions are carried out. Similar muscles, though much less developed, occur in the Echinothuriidae, and must have been present in many extinct Echinoidea in which the plates of the corona overlapped; and hence it is exceedingly probable that from some of these {561}early forms, as, for instance, Bothriocidaris, Holothuroidea may have been evolved. The MUSCULAR BODY-WALL has indeed been as important a factor in the evolution and differentiation of the Holothuroidea as the MUSCULAR ARM in that of Ophiuroidea, or the MOVABLE SPINE in the case of Echinoidea.

There are about 520 species of living Holothuroidea, and of these about twenty-one have been recorded from British waters. One of the best-known of the British species is Holothuria nigra (Fig. 254), commonly known as the "Cotton-spinner"; and this we shall take as a type for special description. The animal may attain a length of a foot when fully extended, and has a diameter of from 3 to 4 inches. It is of a very dark brown colour on one side, which in crawling it keeps uppermost, whilst on the lower side it is of a tawny yellow hue. Three of the radii (often termed the "trivium") are situated on the lower surface; two (termed the "bivium") on the upper surface. The podia are scattered fairly evenly over the whole surface without reference to the radii; below they are regular tube-feet provided with suckers, whilst on the upper surface they are pointed tentacles, employed only for sensory purposes.

If the animal be observed alive and in its natural surroundings, a ring of twenty large tentacles can be seen surrounding the mouth. These buccal tentacles are in every respect comparable with the buccal tube-feet of Ophiuroidea and Spatangoidea, and, like them, are employed in shovelling the muddy substratum on which the animal lies into the mouth.

Ludwig employs the term "feeler" for these buccal tentacles, {562}in order to distinguish them from the pointed podia scattered over the bivium. This procedure will be adopted here. In the Cotton-spinner the feelers, when extended, show a short smooth stem, from the apex of which springs a circle of short branches, which are in turn beset with a double row of branchlets, themselves branched. Such feelers are said to be shield-shaped.

A transverse section through the RADIUS of a Sea-cucumber is, in general, like one through the radius of a Sea-urchin; the points of difference to be noted are: (a) In the Sea-cucumber, beneath the ectoderm, is a thick dermis with small plates scattered in it, instead of the whole dermis being calcified, as is the case in the Sea-urchin; (b) the ampulla of each podium is connected with the peripheral portion by one canal, not two, as in the case of the Sea-urchin; (c) there is a development of coelomic nervous tissue from the outer side of the perihaemal canal; (d) internal to the radial water-vascular canal are to be seen cross-sections of two great bands of longitudinal muscles, by the contraction of which the body is shortened. Lengthening is brought about by the contraction of transverse muscles, which are found on the inner side of the body-wall in each interradius; the five sets taken together act like circular muscles, or a rubber band, on the incompressible fluid in the body-cavity.

When the Sea-cucumber is opened by a cut along the left dorsal interradius, the spacious coelom is laid open, and lying in it is seen the ALIMENTARY CANAL. This tube is bent on itself, so that it has a form like ~ (Fig. 255, B) running backwards to the posterior end of the body, then running forwards to near the anterior end, before it finally turns to run backwards to the anus. By taking cross-sections of the body at different levels, it can be shown that the alimentary canal makes a half-turn round the longitudinal axis (Fig. 255, A). It is suspended by bands of membrane, termed "mesenteries," to the body-wall, and of these there are three, the first of which (i.e. the one nearest the mouth) is attached to the mid-dorsal interradius (Fig. 255, A, M^1), the next to the left dorsal interradius (M^2), and the last to the right ventral interradius (M^3).

The alimentary tube shows four regions, which are distinguished as follows:—(1) A short oesophagus with strongly-marked longitudinal folds in its walls; this is separated by a constriction from (2) the stomach, a very short region, {563}characterised by its strong musculature. Next follows (3) the intestine, a thin-walled tube comprising the middle limb and most of the descending and ascending limbs. This finally passes into (4) the wide terminal "rectum," or "cloaca," which is connected to the body-wall by muscular bands which traverse the coelom (Fig. 256, 10).

The cells lining the oesophagus resemble ectodermal cells; those lining the stomach are nearly all gland-cells, and obviously secrete the digestive juice. The powerful muscles of this portion of the gut produce a strong peristalsis which thoroughly mixes the juice with the food, and in the thin-walled intestine absorption of the digested material takes place. The extreme thinness of the intestinal wall is common to many animals (e.g. Sipunculus, Vol. II. p. 412) which swallow mud and sand for the sake of the organic matter which they contain.

The rectum, or cloaca, is one of the most characteristic features in this and most other Sea-cucumbers. In addition to the passing of faeces, it is used to pump water in and out, and it thus serves as a breathing organ. This pumping is effected by alternate contractions of the radiating muscles attaching the cloaca to the body-wall, and of the circular muscles which immediately surround it. Two long branched tubes termed RESPIRATORY TREES (Fig. 256, 11) open into the cloaca, and into these the inspired water penetrates. The finer branches of these gills end in rounded thin-walled swellings termed "ampullae"; and when water is forced into these they become tense, and a considerable quantity diffuses through their walls, carrying {564}oxygen into the fluid which fills the coelom. If a Sea-cucumber be left in a limited quantity of water, it will sometimes direct the posterior end upwards until it reaches the surface of the liquid, and will pump air into the trees. Besides the trees, other much shorter tubes open into the cloaca, termed the CUVIERIAN ORGANS. These tubes are really the modified basal branches of the trees. They are unbranched, and their peritoneum consists of cells which secrete a slime which swells up enormously on the addition of sea water. When the Cotton-spinner is strongly irritated, it contracts all the muscles of the body-wall, and these, acting on the incompressible fluid in the body-cavity, transmit the pressure to the thin rectum, which tears, and allows a portion of the viscera to be forced out. The first parts to be rejected are the Cuvierian organs, and the cells covering these absorb water, and their contained mucus splits up into a tangle of white threads, in which an enemy may be completely ensnared. A large lobster has been seen so enveloped with this "cotton" as to be completely incapable of motion. The origin of the name "Cotton-spinner" requires no further elucidation. Such self-mutilation, even when it involves not only the Cuvierian organs, but the trees and the whole of the intestine, is not necessarily fatal. If the animal be left alone, it can regenerate the whole of these organs.

The WATER-VASCULAR SYSTEM in its general features resembles that of the Echinoidea. We notice as its first striking peculiarity the modification of the stone-canal. This is often multiplied, as in the species (H. tubulosa) represented in Fig. 256, where there are five; but whether there is one or many, they do not reach the body-wall, but end each in a swelling projecting into and bathed by the coelomic fluid. These swellings are termed "internal madreporites." They are pierced by numerous fine ciliated canals, which lead into a space from which the stone-canal takes its origin. Both stone-canal and madreporite (especially the latter) are stiffened by the deposition of carbonate of lime. In the young Holothurian there is a single ciliated pore-canal opening to the exterior and leading into a thin-walled axial sinus, which, as Bury[505] has shown, is later converted into the internal madreporite; the pore-canal, which represents the external madreporite of other Echinoderms, disappearing at the same time.

{565}[Illustration: FIG. 256.—Dissection of Holothuria tubulosa. × ½. 1, Feelers; 2, feeler-ampullae; 3, ring-canal; 4, Polian vesicle; 5, stone-canals; 6, radial canal; 7, one of a pair of longitudinal muscles; 8, genital tubes; 9, intestine; 10, radiating muscles of cloaca; 11, base of respiratory tree; 12, ventral blood-vessel; 13, plexus of dorsal blood-vessel. (After Ludwig.)]

{566}This extraordinary modification is the consequence of the habit of forcing water into the respiratory trees. The body-cavity is by this means kept tensely filled with fluid, and the stone-canal is enabled to draw on it for the supply to the water-vascular system, thus rendering the external madreporite supererogatory. A large-stalked sac—the Polian vesicle (Fig. 256, 4)—multiplied in many species, hangs down from the water-vascular ring and serves as a reservoir of fluid.

All the podia, including the feelers, have ampullae. In the feelers a semicircular valve is situated just where the external part passes into its long ampulla. When this valve is expanded, the feeler is moved about by the contraction of its muscles, but when it is contracted, the contents of the feeler can flow back into the ampulla, so that the feeler is reduced to an insignificant papilla (as in Fig. 254). The interior of the feeler is ciliated, and a current seems to flow up one side and down the other, so that this organ, like the dorsal tube-foot of a Cake-urchin or Heart-urchin, seems to assist in respiration.

The NERVOUS SYSTEM differs from that of Echinoidea in the absence of the pigment spot (or so-called eye) on the terminal podium of the radial water-vascular canal. Each podium receives a so-called nerve—really an extension of the radial nerve-cord with its ganglion-cells—and this ends in a plate of sensory epithelium in the sucker of the tube-foot or tip of the tentacle, or of each of its branches in the case of the feeler.

There is a coelomic nervous system developed from the radial perihaemal canals. The PERIHAEMAL RING is represented in Echinoidea by the lantern coelom, in Holothuroidea in all probability by the "buccal sinus," a space intervening between the water-vascular ring and the oesophagus. In the outer wall of this are developed ossicles, which constitute the CALCAREOUS RING found in all[506] Sea-cucumbers (Fig. 257, A and B). In this ring (Fig. 257, B) are to be distinguished radial and interradial pieces. The former are notched at their upper ends, and in all probability represent the auriculae of Echinoidea, as the radial nerve-cords pass out over the notches, whilst the interradial pieces probably represent a coalesced pair of jaws and their included tooth, since these ossicles develop from a single rudiment in the larval Echinoid.

{567}The so-called BLOOD SYSTEM is in its main features similar to that of Echinoidea. It consists of a blood-ring surrounding the oesophagus inside the water-vascular ring, and sending branches along the stone-canal, and of dorsal and ventral strands accompanying the gut in its course. These are best marked in the region of the intestine, where absorption principally takes place; in the wall of the stomach they are represented by a delicate plexus which can hardly be traced into connexion with the blood-ring. The dorsal "vessel" is situated in a fold of peritoneum projecting from the intestinal wall; it gives off branches to the intestine, which unite on its surface to form a plexus. In the middle limb of the intestine these branches are grouped into tufts, and the fold of peritoneum between successive tufts becomes absorbed; through the holes so formed branches of the respiratory tree penetrate, so that the trees cannot be separated from the intestine without tearing the dorsal vessel (Fig. 256, 13).

The GENITAL ORGANS consist of a single group of branched tubes situated on the left side of the dorsal mesentery, which converge to open into a short genital duct, which leads to a pore situated in the mid-dorsal line, a short distance behind the feelers. From the common point of origin of the tubes, the "genital base," as it is called, a worm-shaped genital stolon[507] extends back along the genital duct towards the body-wall. There is no genital rachis.

CLASSIFICATION OF HOLOTHUROIDEA.

The class is in many points of structure exceedingly variable, but many striking variations in important organs occur in allied {568}species, and even in the same species, and hence are probably not of physiological importance. We shall therefore confine our attention mainly to those differences in structure which are correlated with differences in habits, and therefore of systematic importance. We shall consider in order (1) the feelers; (2) the method of protecting these; (3) the rest of the water-vascular system; (4) the gills; and (5) the skeleton.

FEELERS.—These organs have been made the basis of the division of the Holothuroidea into orders, and as they are the means by which food is obtained, and are thus of first-class physiological importance, this procedure is fully justified. In three orders they have the shield-shaped ends described in the case of Holothuria nigra, but in another large order (Dendrochirota) they are much branched, and end in a mass of delicate twigs. In another order (Synaptida) they are feather-shaped, with two rows only of branches, whilst finally in Molpadiida they are simple finger-shaped processes with one or two lateral branches. The number of the feelers varies from ten to thirty.

In the Dendrochirota the entire anterior portion of the body can be introverted into the interior, so that in this way the crown of feelers can be effectively protected. The retractor muscles are modified portions of the longitudinal muscles of the body-wall, which traverse the body-cavity, and are inserted into the radial pieces of the calcareous ring. Similar muscles are found in the genus Molpadia and in many of the Synaptida. In Aspidochirota and Pelagothuria they are totally wanting, and here the feelers possess long ampullae which allow of the tentacles being individually contracted to very small dimensions. These ampullae seem to be present in nearly all cases in Molpadiida, and in Synaptida, although in the last-named order they are very feebly developed, and must be looked on as vestigial. In Dendrochirota, owing to the strongly developed retractors, they would be useless, and so are absent.

WATER-VASCULAR SYSTEM.—In Synaptida the radial canals are totally absent in the adult, and the only podia are the feelers, which spring directly from the ring-canal. The radial canals are present in Pelagothuria, but the feelers are still the only podia; in the Molpadiida there are only five small terminal tentacles round the anus in addition to the feelers. In the Elasipoda all the podia have pointed ends, but the dorsal podia {569}are few, long, and stiff, and often coalescent in places to form grotesque or remarkable appendages. In the remaining forms the podia of the trivium have always suckers, whilst those of the bivium may or may not be pointed. In Psolus the two dorsal radial canals and their podia are totally absent.

RESPIRATORY TREES.—These are present in Aspidochirota, Dendrochirota, and Molpadiida, totally absent in the Synaptida and Pelagothuria, and doubtfully represented in a few Elasipoda by a single unbranched outgrowth of the gut.

SKELETON.—This consists, as explained above, of the scattered deposits in the skin and of the calcareous ring. As regards the first, their shape varies immensely, and yet one or two principal types characteristic of each of the main divisions can be defined. Thus the Synaptida are characterised by wheels, with spokes ending in a hub, and by anchors attached to a plate. The Elasipoda have simple St. Andrew's crosses, whilst the Aspidochirota are mainly characterised by "stools" (Fig. 257, C) and buckles (Fig. 257, D). The Dendrochirota have a bewildering variety of forms; the most characteristic, however, are a right-angled cross and a grating, very similar to the buckles of the Aspidochirota, except that in the former there are usually four holes placed cross-wise, whilst the buckle has generally two parallel rows of three holes. Since these ossicles are the only records we possess of the existence of fossil Holothuroidea, they have been studied with great care. The calcareous ring varies very much. The radials are always five (except in individuals where there are more than five radii), but the interradials are increased in the Synaptida, and in the other orders are in some cases diminished or occasionally suppressed altogether. The last is the case in nearly all Elasipoda; here the radials consist of a central horizontal piece with two diverging arms at each side. These arms, which can branch repeatedly, traverse the adjacent interradii, meeting those of the next radii, so that interradials are in most cases entirely absent. The Aspidochirota have usually a ring consisting of small squarish ossicles (Fig. 257, B). In the Molpadiida and Dendrochirota the radials are prolonged backwards into forked tails, which in some Dendrochirota are broken into a number of small pieces (Fig. 257, A), the lower parts of the interradialia being similarly divided.

The CLASSIFICATION of the Holothuroidea is comparatively easy. {570}All authors recognise six divisions, and the only dispute is as to whether they are to be regarded as families or orders. Ludwig[508] divides the group into two orders, PARACTINOPODA and ACTINOPODA, but the first includes only those forms which have lost the radial canals, and this is only one step farther in a degeneration, intermediate stages of which can be traced in the other divisions. There is really no ground for placing the Paractinopoda in contrast to all the other divisions, and the only alternative is to regard the six main divisions as orders, since a class must be divided into orders. In the case of only one, however, is a further division into families practicable, and therefore each of the others will contain a single family.

ORDER I. ASPIDOCHIROTA.

Holothuroidea with shield-shaped feelers provided with ampullae; with radial canals and numerous podia and with respiratory trees. Retractor muscles absent. Nearly a third (158) of the species of Holothuroidea belong to this order, but there are only six genera, and of these Holothuria includes no less than 109 species. The Aspidochirota seem for the most part to live on somewhat firm ground, the surface of which they are continually sweeping with their shield-shaped feelers, which brush the adherent organisms into the capacious mouth. Four species of Holothuria—viz. H. intestinalis, H. tremula, H. aspera, and H. nigra are recorded from British waters. The first-named is a northern form, distinguished by the fact that all its podia have suckers; it is found in the north of Scotland. H. tremula is intermediate in structure between H. intestinalis and H. nigra, and is found in deep water off our western coasts. H. aspera, remarkable for the radiating spines growing out from its ossicles, has been recorded only once from deep water. Of the other genera it is only necessary to mention Stichopus, remarkable for the square outline of its transverse section, and for the restriction of the ventral tube-feet to the radii; there is also a well-marked tapering of the anterior end, so that this genus may be said to have a neck. Stichopus is almost entirely confined to tropical waters, and some of its species, as also species of the ubiquitous genus Holothuria, as well as many other undetermined species, constitute the valuable "Trepang," which is a delicacy much prized {571}by the Chinese. The Trepang are caught in various parts of the Malay Archipelago. They are cooked in sea water to preserve them, dried in the sun, and boiled in fresh water repeatedly, till all the salt is extracted. They are then dried and sent to market, where they are used in making soup.

ORDER II. ELASIPODA.

Holothuroidea with shield-shaped feelers, destitute of retractor muscles; all the podia have more or less pointed ends,[509] but there is a marked contrast between dorsal and ventral podia, and the ventral surface is flattened so as to constitute a creeping sole. No respiratory trees, at most a simple diverticulum of the intestine; frequently the primitive external madreporite is retained, and contains several pores.

A number of spherical sacs containing little spherical calcifications (otocysts) are attached to the nerve-ring in some genera. Can these be metamorphosed sphaeridia of Echinoid ancestors?

The first member of this remarkable order to be discovered was Elpidia, which was dredged in 1875 by the Swedish Arctic Expedition, and described by Théel.[510] The majority of the known members of the order were discovered by the dredging expedition of H.M.S. "Challenger." The species composing it are, with one exception, inhabitants of what may be termed the abysmal depths of the sea. The exception alluded to (Ilyodaemon maculatus) is confined to the belt between 100 and 150 fathoms in depth. The well-marked sole and the absence of suckers point to a life consisting of constant peregrinations over {572}the soft ooze forming the ocean floor. The ooze forms their food, and as their weight must to a certain extent immerse them in it, we can understand why the stiff, long dorsal podia have been specialised as respiratory organs, since there are no respiratory trees. These respiratory podia sometimes undergo extraordinary development; thus in Peniagone several very long ones cohere to form a huge vertical sail, whilst in Psychropotes one or two cohere to form a backwardly projecting tail. On the other hand, in Ilyodaemon (Fig. 258) the dorsal podia are numerous and slender.

ORDER III. PELAGOTHURIIDA.

Holothuroidea with shield-shaped feelers provided with long ampullae which project outwards, pushing the skin before them so as to form external appendages, connected at the base by a web. Calcifications absent. No retractor muscles. No respiratory trees. The external madreporite is retained, but all podia other than the feelers have disappeared, although the radial canals have been retained.

This order contains one species, Pelagothuria natans, which is the only free-swimming Holothuroid known, the muscular web connecting the freely projecting ampullae being the organ of locomotion.

ORDER IV. DENDROCHIROTA.

Holothuroidea with long repeatedly branched feelers terminating in fine pointed twigs. No feeler-ampullae; but retractor muscles are present, which can introvert the anterior end of the body. Respiratory trees well developed. This order includes twelve genera and over 180 species, and, like the Aspidochirota, is of worldwide distribution. So far as can be safely generalised from the few species whose habits have been closely observed, it seems that this order is adapted to catch swimming prey—it is an order of fishers. The long branched tentacles are extended like the lines of an angler. Their surface is coated with adhesive slime, and before long becomes covered with small organisms which have come in contact with it. When a feeler has captured in this way a large enough haul, it is turned round and pushed into the mouth, which is closed on it. It is then forcibly pulled out, during which process the prey is, so to speak, stripped off it. {573}Four genera (Cucumaria, Thyone, Phyllophorus, and Psolus) and sixteen species have been recorded from British waters.

Cucumaria is remarkable for being the only genus of Holothuroidea in which the body is pentagonal in cross-section. In the majority of its species the tube-feet are confined to two rows along each radius, but in a few there are some scattered tube-feet in addition. There are only ten buccal tentacles. The species figured (C. crocea) is an Antarctic one which carries the young on the back. Thyone differs in being circular in cross-section and in having the tube-feet scattered evenly over the whole surface. In Phyllophorus (Fig. 260) the tentacles are more than fifteen, and are disposed in two circles, an inner of smaller and an outer of larger tentacles. The other podia are, as in Thyone, scattered.

{574}[Illustration: FIG. 260.—Phyllophorus urna. × 1.]

Psolus is a most extraordinary genus. There is a well-marked sole, to which the tube-feet are confined, whilst the dorsal radial canals, and consequently all the dorsal tube-feet, are absent. The dorsal ossicles are enlarged to form a complete mail of plates, recalling the corona of a Sea-urchin. The two British species are small, and found in comparatively deep water, but a fine large species is found in the Gulf of St. Lawrence, and {575}extends into brackish water up the estuary. The species figured (P. ephippifer) is an Antarctic one, which carries the eggs until development is complete in a dorsal brood-pouch.

ORDER V. MOLPADIIDA.

Holothuroidea with simple, finger-shaped feelers, provided with ampullae; retractor muscles occasionally present; respiratory trees present. Besides the feelers, the only podia are five minute papillae terminating the radial canals in the neighbourhood of the anus.

This order includes six genera and about thirty species. Its peculiarities seem to be due to the fact that its members are burrowers, leading a life like an earthworm. Hence the absence of the tube-feet, and the small, almost vestigial character of the feelers. Trochostoma (Fig. 262) and Caudina are remarkable for the presence of a tail. This appendage is in reality only the narrow posterior end of the body, and is especially long in Caudina; and observations on a species found off the coast of Maine, U.S.A.,[511] have shown that the tail, like the siphon of a Mollusc, projects up from the burrow to the surface in order to maintain the respiratory current of water.

ORDER VI. SYNAPTIDA.

Holothuroidea with short bipinnate (i.e. feather-shaped) feelers, provided with only vestigial ampullae, and with well-developed retractor muscles. No other podia; radial canals absent in the {576}adult. Respiratory trees absent, and transverse muscles of adjacent interradii continuous, so as to form circular muscles. Otocysts attached to the nerve-ring as in Elasipoda.

The members of this remarkable order, like those of the preceding one, are burrowers; but though their feelers are larger, the rest of their anatomy has undergone much more profound modification than that experienced by the Molpadiida. The loss of the radial canals, which must be practically functionless in Molpadiida, is not a great step, but the change in the mode of respiration is a greater modification. Respiration appears to be effected by diffusion through the body-wall, which is always comparatively thin. The circulation of the body-cavity fluid is assisted by a number of stalked, ciliated cups placed on the mesenteries near the line of their insertion on the body-wall. In dealing with Asteroidea it was pointed out that the ends of the tube-feet are the only places where numerous sense-hairs are to be found, and which, therefore, can be called sense-organs. This is true generally throughout Echinodermata. Now in Synaptida, where the tube-feet are lost, the surface of the body has scattered over it little sense-organs consisting of hillocks of ectoderm with an aggregation of sense-cells. These may be regarded as representing the discs of the missing tube-feet. One is involuntarily reminded by the ciliated cups and scattered sense-organs of the ciliated urns and sense-organs of the Sipunculidae, which lead a similar life; and taking into consideration the general superficial likeness in {577}appearance of the two groups, the epigram is almost justified that "if the Synaptida were not extremely careful they would become Gephyrea."

This order is represented in British waters by three species of the genus Synapta, which is remarkable for possessing, as ossicles, only the peculiar anchors attached to anchor plates. The present author has dug up the commonest species (S. inhaerens) from its burrows in the sand at low water in the Clyde. These animals seem to seek their food at the surface; the feather-shaped feelers are used to seize small algae and zoophytes, of which the food apparently consists. If seized, S. inhaerens readily amputates the posterior part of the body, whilst the head with its feelers immediately buries itself. The other genera of the order (except Anapta) are characterised by the possession of wheels with spokes as their characteristic ossicle, as the names Trochodota, Trochoderma, Acanthotrochus bear witness.

The only fossil remains of Holothuroidea consist of isolated ossicles—wheels, gratings, anchors, etc.—which first make their appearance in the Carboniferous limestone and tell us practically nothing of the evolution of the group. From a comparison with one another of the living families, certain conclusions can be drawn. The Aspidochirote feeler and the method of using it recall forcibly the shape and function of the buccal tube-feet of Spatangoidea. It is probably safe to assume that it is the primitive form from which the other forms of feeler have been derived. Secondly, the anal respiration and the curious internal madreporite have been developed in correlation with one another, and are like nothing found elsewhere among the Eleutherozoa. Hence we may with high probability assume a Protoholothuroid stock with shield-shaped feelers but devoid of respiratory trees, and with an external madreporite. From this stock the Elasipoda developed by migrating into deeper water, whilst the Pelagothuriida sprang from the same root by taking to swimming; the Aspidochirota constituting the main line. The Dendrochirota were developed from a stock with respiratory trees and internal madreporite—in a word, from Aspidochirota. From them the Synaptida and the Molpadiida have developed as offshoots at different periods through taking to a burrowing life. These relationships are shown by the following diagram:—

Protoholothuroidea {578} / | \ / | \ Elasipoda | Pelagothuriida | Protaspidochirota / \ Aspidochirota Protodendrochirota |\ | Synaptida |\ | Molpadiida | Dendrochirota

{579}CHAPTER XX

ECHINODERMATA (CONTINUED): PELMATOZOA—CRINOIDEA = SEA-LILIES—THECOIDEA—CARPOIDEA—CYSTOIDEA—BLASTOIDEA

SUB-PHYLUM II. PELMATOZOA

The PELMATOZOA differ from the ELEUTHEROZOA in several important respects. They are fixed (at any rate in the young stage) by the centre of the aboral surface, and this portion of the body usually takes on the form of a stem supported by a definite series of ossicles, so that we can discriminate a "calyx"—the main part of the body—from the "stem." Further, the podia and the ambulacral grooves seem to be always covered with powerful cilia, which are employed in producing a current which sweeps small organisms to the mouth. The podia are never locomotor in function; their use is similar to that of the tentacles on the lophophore of Polyzoa and Brachiopoda.

The living Pelmatozoa are very few in number compared with the extinct forms. It may with justice be said that the group is nearly extinct; indeed, out of its five classes one alone, and that the most highly specialised class, survives till the present day. Now we have already seen that, in the case of the Eleutherozoa, if the annectant fossil types were taken into consideration, the definition of the classes would be difficult, so that it is not to be wondered at if the classes of the Pelmatozoa are also somewhat difficult to define; and it must be added that this difficulty is not only due to the fact that intermediate types occasionally occur, but also to our ignorance of the functions of many structures found in fossil types, speculations regarding which are to be received with caution. Bearing in mind, then, the provisional nature {580}of the classification, we may give the diagnoses of the principal divisions as follows:—

Class I. CRINOIDEA.—Pelmatozoa provided typically with a well-marked stem; calyx consisting of an aboral "patina" of two or three circles of plates, and a flexible "tegmen" or oral surface with small plates or none; radial canals supported by long branched arms, which are developed as direct prolongations of the uppermost circle of plates in the patina.

Class II. THECOIDEA (Jaekel) = EDRIOASTEROIDEA (Bather).—Pelmatozoa without a stalk, fixed to the substratum by the whole aboral surface. The radial canals run out over the oral surface in grooves, which are closed by specially modified plates; but there are no arms of any kind.

Class III. CARPOIDEA (Jaekel).—Pelmatozoa with a well-developed stalk. The radial canals and their branches are devoid of a skeleton, and either produce no modifications at all on the skeleton of the calyx, or at most are supported by short horn-like outgrowths of some of its plates.

Class IV. CYSTOIDEA.—Pelmatozoa which typically possess a well-developed stalk, a sac-like calyx contracted at the mouth and covered with plates, some of which are pierced with pores or slits; the radial canals, though they may for part of their course run over the surface in grooves, have their terminal portions supported by free unbranched arms ("fingers").

Class V. BLASTOIDEA.—Pelmatozoa provided with a well-developed stalk and ovoid bud-like calyx. From the mouth the radial canals run backwards over the calyx, as in Echinoidea, but they give rise to numerous lateral branches, which are supported by free unbranched arms ("fingers"). Special respiratory organs occur on the interradial areas in the form of parallel folds called "hydrospires."

CLASS I. CRINOIDEA

This is the only class which has living representatives. There are twelve recent genera, of which eight retain the stalk throughout life; the remaining four lose it when adult, retaining only a stump, termed the "centro-dorsal," covered with fixing organs ("cirri"). The stalked forms are confined to considerable depths, and can only be obtained by deep dredging, whereas many of the {581}stalkless forms are comparatively common. We shall select as type for special description the common Feather-star, Antedon rosacea (bifida), which can be dredged in depths of ten fathoms off the south-west coast of England.

The animal consists of a small flattened calyx, from which radiate out ten long delicate arms, each fringed with a double series of short branches called "pinnules." In the centre of the aboral surface can be seen the centre-dorsal plate (Fig. 265, c), a knob-like stump of the broken-off stem, covered with small whip-like outgrowths called "cirri," by means of which the animal is anchored to the substratum (Fig. 265, cir). When Antedon is disturbed it relaxes its hold, and swims by graceful muscular movements of the arms. These are arranged in five pairs, and the corresponding members (right and left) of all the pairs are bent and relaxed together. On coming to rest the animal reattaches itself by means of the cirri. These are composed of cylindrical ossicles joined to one another by muscles, and they can thus act as efficient grasping organs. In the centre of the oral surface, which is termed the "tegmen," and is soft, flexible, and without visible calcifications, is situated the mouth, surrounded by five short triangular flaps called "oral valves." In the intervals between these valves, grooves radiate from the mouth which bifurcate at the points of origin of each pair of arms, and are continued over their surfaces. These grooves correspond to the ambulacral grooves of Asteroidea, and to the epineural canals of the other classes of Eleutherozoa. At each side of each groove {582}are to be found a series of podia in the form of delicate finger-like processes, which serve only for respiration and for producing a current of water, their surfaces, like that of the grooves between them, being covered with powerful cilia. The anus is at the extremity of a little knob called the anal papilla, situated in one of the interradii (Fig. 264, an).

As in Ophiuroidea, the ectoderm cells have disappeared over the whole surface of the body, except the grooves and the podia, the only trace of their former existence being a cuticle with adherent nuclei. Pedicellariae are unknown in all Pelmatozoa; and spines have only been described from one fossil species of Crinoid. Beneath the cuticle is the dermis, having the composition described in the case of Asterias rubens; this on the aboral side of the calyx gives rise to the "patina," consisting of plates, in part movable on one another, in part immovably fused together. Those visible from the outside are (1) the centro-dorsal ossicle, from which the cirri spring; (2) five columns of ossicles termed radials (Fig. 266, R^1, R^2, R^3); each column consists of three radials, extending from the centro-dorsal to the origin of a pair of arms. The uppermost radial in each column bears two facets for the articulation of these arms. Each arm is supported by a series of "brachial ossicles" (Br).

It is evident, both from the number of ambulacral grooves and of the columns of radials, that Antedon has only five radii, and each pair of arms must be regarded as having arisen by the bifurcation of a primitive arm. This is proved to be true by {583}a study of the development, and it can further be shown that the arms fork repeatedly; but in these further bifurcations one fork remains short, and forms a pinnule, whilst the other continues the arm. Thus the arm, instead of being a single axis, is really a series of axes—in a word, it is a "sympodium."

If in the case of any bifurcation the two forks were to develop equally, the number of arms in that ray would be doubled, and this actually happens in the case of other species of Antedon.

DIGESTIVE SYSTEM.—The mouth leads through a short vertical oesophagus into an enlarged stomach, which lies horizontally curved around the axis of the calyx. The stomach is succeeded by a short intestine, which leads into the anal papilla. Both oesophagus and stomach are ciliated, and the food consists of minute organisms, swept into the mouth by the current produced by the cilia covering the ambulacral grooves and podia; the ten arms may indeed be compared to a net spread out in the water to catch swimming prey.

The WATER-VASCULAR SYSTEM consists of a ring closely surrounding the mouth, from which radial canals are given off which underlie the ambulacral grooves and bifurcate with them. The podia have no ampullae, but muscular strands traverse the cavities of the radial canals, and that of the ring-canal, and by their action water can be forced into the podia, which are thus extended. Numerous stone-canals hang down from the ring-canal, and open freely into the coelom; they do not, as in Holothuroidea (where the same arrangement occurs), end in sieve-like madreporites. The tegmen, i.e. the ventral surface of the calyx, is pierced by a number of isolated pores lined by ciliated cells, which suck in water. In the oldest Pelmatozoa there seems to have been a regular madreporite. In the larva of Antedon there is but one pore-canal, which, as in most Eleutherozoa, leads into a special section of the coelom, the "axial sinus," embedded in the body-wall, with which also the single stone-canal communicates; but later the division between the axial sinus and the rest of the coelom breaks down, and then the pore-canals and stone-canals become multiplied independently of each other (Fig. 266, m.p, p.c, and st.c).

NERVOUS SYSTEM.—In the young stalked form the nervous system, as in other Echinoderms, consists of a ring round the {584}mouth, from which radial cords are given off which run under the ambulacral grooves (Fig. 266, nerv.rad.v).

The fibres of this nervous system are, as in Asteroidea, immediately beneath the bases of the ectoderm cells. A large band of fibres is given off to each podium, which is covered with minute elevations, each with pointed sense-hairs in the centre. As the animal grows, another nervous system makes its appearance, which is developed from the coelomic wall, the cells of certain tracts of which multiply and bud off ganglion cells from which the fibres grow out.

This "aboral nervous system," as it is called, has its centre in the "chambered organ" (Fig. 266, chamb), which is embedded in the centro-dorsal ossicle, and is roofed over by a plate called the "rosette." This represents the five coalesced "basals," a ring of plates which in other forms alternate with the lowest radials, and it intervenes between these and the centro-dorsal. The chambered organ consists of a ring of five vesicles, which have originated as pouches of the aboral coelom (Fig. 266, chamb). The walls of these vesicles develop nervous matter; from them radiate out five great cords, deeply embedded in the {585}plates of the patina. These cords rapidly fork, and one division of each of two adjacent cords enters the lowest radial. In the third radial all the cords are connected by a commissure which runs completely round the calyx. Each of the cords in the third radial forks again, and one branch of each cord enters each of the two arms connected with it, and the two branches entering an arm coalesce to form a single cord. In the arms, as in the calyx, the cords are deeply embedded in the ossicles, but branches extend to the ventral surface of the arms and here unite to form two longitudinal cords, one on each side of the groove. In the tegmen these cords are connected by an outer nerve-ring, branches from which join the ectodermal nerve-ring already described.

The researches first of W. B. Carpenter[512] and then of Marshall[513] have proved that it is the aboral nervous system which really controls the movements of the animal. If the chambered organ is destroyed by cautery, the whole movements of the animal are paralysed; but it will carry out its characteristic swimming movements just as well if the whole tegmen with the ambulacral nerve-ring and the whole of the alimentary canal are torn away. The commissure in the third radials co-ordinates the movements of the arms. If it is cut they move independently of one another. The position of the radial cords inside the ossicles is gradually acquired. At first they are gutter-like evaginations of the coelom; by upgrowth of their sides the gutters become canals, and are then surrounded by calcified tissue. The cirri have each a cord traversing them which originates from the chambered organ.

COELOM.—In the young stalked form the coelom consists of the water-vascular system ("hydrocoel"), and underlying it an oral coelom, separated from an aboral coelom by a horizontal mesentery. As the animal grows, this horizontal mesentery becomes largely absorbed, and the coelom becomes everywhere traversed by cellular cords (trabeculae), which are later calcified.

Both oral and aboral coelom become, like the hydrocoel, bent into hoops, and along the axis of the aboral coelom a cord of germ-cells is developed, which constitutes the "genital stolon." The chambered organ is developed from the aboral coelom, and {586}in the centre of its five chambers a median pocket grows down into the centro-dorsal, along the side of which is an extension of the genital stolon. In the arms the mesentery separating the extensions of the oral and aboral coelom persists; the oral extension consists of two parallel canals called "subtentacular" (Fig. 267, s.c), whilst the aboral space is termed the "coeliac" canal (Fig. 267, c.c). In the tip of the pinnule, that is to say at the extremity of a ramification of the arm, the coeliac and subtentacular canals communicate. As portions of the lining of both canals are ciliated, a circulation of the coelomic fluid is thus kept up. The GENITAL STOLON gives rise at the level of the remnant of the horizontal mesentery in the disc to a circular genital rachis, whence cords pass down the arms in the tissue separating subtentacular and coeliac canals (Fig. 267, g.r). Each cord is contained in a special tube, the "genital canal," which is probably developed in the same way as the aboral sinus of the Eleutherozoa, i.e. as a special sheltering outgrowth of the coelom (Fig. 267, g.c). In the pinnule the rachis swells out into a genital organ, from which a short duct is developed when the organ is mature. The eggs are large (3 mm. in diameter), and adhere for a considerable period of their development to the pinnules.

{587}The MUSCLES of Antedon are of two kinds. Those of the water-vascular system are, as in Eleutherozoa, basal outgrowths of the cells forming the walls of the system. The muscles moving the joints of the arms appear to be modifications of connective-tissue cells. When the brachials are isolated their terminal faces, strikingly long, recall those of Ophiuroid vertebrae. There is a ventral groove for the coelomic canal. Above this groove the face is divided by ridges into four areas for attachment of the muscles. Dorsal to this is the pit for the strong ligament which binds the ossicles together; then comes the canal for the aboral nerve-cord, whilst dorsal to this is the pit for what is called the "dorsal elastic ligament." The theory underlying this name is that the muscles bend the arms ventrally, and the ligament by its elasticity restores them to their places; but there seems reason to believe that the "ligament" is really a dorsal muscle. It is particularly to be noted that similar muscles occur between the first and second radials, proving that the primary arm really begins with the first radial. The second and third radials, as also the first two ossicles and certain others of each arm, are closely united by calcified fibres, and this kind of union is called a "syzygy" (Fig. 265, syz). The cirri have all their ossicles united by muscular attachment, and can move rapidly.

The BLOOD SYSTEM (see pp. 449-451) forms a ring consisting of a network of strings round the oesophagus. This is termed the "labial plexus." From this cords can be traced to the wall of the stomach and to the surface of the genital stolon. The assertion that radial strands intervene between the ectodermic nerve-cord and the radial water-vascular canal, though usually made, does not appear to be justified, since what is termed the vessel appears to be a crevice formed by shrinkage in preservation.

The process of respiration is doubtless largely carried out by the podia, but it must be assisted by the constant instreaming of fresh sea-water through the pore-canals. The process of EXCRETION has not been directly observed in Antedon, but structures called "sacculi" may be connected with this function. These are spherical masses of amoebocytes embedded in the tegmen. During life they are colourless, but after death they become coloured, showing that they secrete a peculiar compound. These sacculi abound in the disc, and a row of them is to be found at each side of the ambulacral groove in the arms. When, as in {588}tropical species, the groove is supported by side-plates, these are notched for the reception of the sacculi.

Turning now to survey the group Crinoidea as a whole, lack of space forces us to confine our attention mainly to the living forms. These differ amongst themselves chiefly in the following points: (1) the condition of the stem; (2) the structure of the calyx; (3) what is intimately connected with this, the method of branching of the arms; and (4) the length of the alimentary canal.

CONDITION OF THE STEM.—This is represented by a centro-dorsal stump in Antedon and most of its allies, but in Actinometra it becomes a flat plate, and in some species in old age all the cirri drop off. In Uintacrinus and Marsupites (fossil genera) there is no trace of cirri. In Pentacrinidae there is a long stem, pentagonal in cross-section, in which alternate ossicles carry whorls of cirri; in Rhizocrinidae the stem consists of compressed ossicles, elliptical in section, bearing cirri only at the rooting tip, whilst in Hyocrinus the stem is made up of cylindrical ossicles, cirri being apparently absent. Finally, in Holopus the stem is represented by an uncalcified leathery outgrowth from the calyx.

SKELETON OF CALYX AND ARM.—In living Crinoidea, with the doubtful exceptions of Holopus and Hyocrinus, the calyx is supposed to be built up originally of four whorls of plates, viz. "infra-basals," "basals," "radials," and "orals," the last named forming the skeleton of the oral valves round the mouth. In the two exceptions named there is no certain evidence of the existence of infra-basals. In living forms the infra-basals coalesce with the uppermost joint of the stem; the basals remain large and conspicuous, though they are fused into a ring in Rhizocrinidae, Atelecrinus, and Thaumatocrinus, whilst in Pentacrinidae this ring is nearly, and in Antedon and its allies completely, hidden when the calyx is viewed from the outside. In Hyocrinus the basals are represented by three ossicles. The lowest radials are an important element in the patina in every case, but the upper radials, the incipient portions of the arms, may be incorporated in the calyx (Pentacrinus, Antedon) or may be free (Rhizocrinidae and Hyocrinus); in Metacrinus there are five to eight radials in each column, all incorporated.

The oral plates are very large in Hyocrinus, Holopus, and {589}Thaumatocrinus, small in Rhizocrinus, vestigial or absent in Bathycrinus, and completely absorbed in Antedon. In addition to these main elements, in many species small accessory plates are developed (a) at the sides of the ambulacral groove, over which they can close down (many species of Antedon, Hyocrinus, Holopus, Rhizocrinidae, some species of Pentacrinidae); these are "covering plates," and correspond in function to the adambulacrals of Asteroidea; (b) supporting the sides of the groove and corresponding to the ambulacrals of Asteroidea;[514] these are "side-plates," and the covering plates articulate with them; (c) on the surface of the tegmen; these are the interradial plates, which in Thaumatocrinus alone among recent forms, but in many fossil forms, are continued into the patina, where they separate the radial plates.

MODE OF BRANCHING OF THE ARMS.—All modern Crinoids have pinnules, and this, as has already been explained, is due to a suppressed dichotomy. The extent of the suppression determines the number of arms, which varies within the same genus.

ALIMENTARY CANAL.—In Hyocrinus there is no dilatation which could be called a stomach; in Actinometra the mouth is excentric, and the anal papilla occupies the centre of the tegmen. The intestine is elongated, and describes several turns round the papilla before ending in the anus.

The CLASSIFICATION of Crinoidea cannot properly be considered without taking account of fossil forms, but to do so at all adequately is impossible on account of limitations of space. Less regret may be felt because the three specialists in this branch, viz. Bather in England, Springer in America, and Jaekel in Germany, come to fundamentally different conclusions on the subject. If we confine our attention to living forms we may, with P. H. Carpenter,[515] select the stem as the basis of classification. As the method of gaining food is the same in all cases, the Crinoidea have probably split on the method of attachment to the substratum. These families—it is impossible, in view of the greater range of variety in fossils, to dignify them with the name of orders—are as follow:—

{590}FAM. 1. HYOCRINIDAE.—Stem long and persistent; cirri absent; stem ossicles cylindrical—ligaments uniting them not specialised. Arms (five) short, but with extremely long pinnules. Patina composed of long exposed basals and a ring of five spade-shaped radials. Five large persistent orals. Interradials and covering plates present. One species (Hyocrinus bethellianus, Figs. 268, 269) dredged up in the Southern Pacific Ocean.

FAM. 2. RHIZOCRINIDAE.—Stem long and persistent; cirri confined to a few near the root or replaced by rooting branches of the stem. Stem-ossicles thin and pentagonal at the summit, but lower down compressed, elliptical in section, and united by two ligaments separated by a transverse ridge for articulation. Patina composed of exposed basals and a ring of five short radials. Orals large {591}or vestigial. Covering plates and interradials present. Two genera, both from great depths in the Atlantic—Rhizocrinus (Fig. 270), with five arms and well developed orals (attachment by branching root-cirri); and Bathycrinus, with ten arms and vestigial orals; attachment by root-like branches of stem (this is essentially the same as root-cirri).

FAM. 3. PENTACRINIDAE.—Stem consisting of ossicles which are pentagonal in section, united in pairs by syzygy, the upper one of each pair bearing a whorl of cirri and united by five bundles of fibres of petal-like section with the lower one of the pair above it. No rooting processes. Patina consists almost entirely of columns of radials, the basals being almost or completely hidden. Orals absent, but side-plates in the ambulacral grooves. Two recent genera, Pentacrinus (Isocrinus), with three radials in each column; Metacrinus, with five to eight radials in a column, but the third {592}radial bears a pinnule. Pentacrinus is found in both the Caribbean Sea and the Pacific Ocean; Metacrinus in the Pacific. It appears that the Pentacrinidae when young are attached by a foot-plate at the apex of the stem; but when adult, the stem is broken in two and the animals, like Antedon, swim by movements of the arms, dragging a large part of the stem after them, by which they effect temporary attachment. As in other stalked forms, the cavities of the chambered organ are prolonged into canals which traverse the stalk; but in this family there is the peculiarity that a repetition of the chambered organ is found opposite every whorl of cirri.

FAM. 4. HOLOPODIDAE.—Stem represented by a leathery noncalcified outgrowth from the base of the calyx; one circle of radials indistinguishably fused with the basals and with each other to form the walls of the calyx. Large oral plates, ten short arms. One genus, Holopus, in shallow water in the Caribbean Sea.

{593}[Illustration: FIG. 272.—Arms and portion of stem of Pentacrinus maclearanus, slightly enlarged. In this species the basals can be seen. (From Wyville Thomson.)]

{594}[Illustration: FIG. 273.—Calyx of Actinocrinus, one of the Camerata, broken open to show structure. amb, Ambulacral groove enclosed in covering plates; B, basal; R^1, R^2, R^3, the three radials of a column. (After Zittel.).]

FAM. 5. COMATULIDAE.—Stem in the adult broken off, leaving only a stump, the centro-dorsal, covered with cirri. Six genera. Antedon (= Comatula) has already been described; many tropical species have numerous arms and often side-plates and covering plates. Actinometra is distinguished by its excentric mouth, and by the fact that the centro-dorsal is flat and has cirri only round its edges; Atelecrinus has an acorn-shaped centro-dorsal, and the basals are externally visible; Eudiocrinus differs from Antedon only in having five arms; Promachocrinus is a remarkable form, having ten radii (this is a unique feature in Crinoidea); finally, Thaumatocrinus has basals externally visible, large persistent orals and interradial plates, and in addition a short free appendage of several plates on the anal interradius. Antedon and Actinometra are almost world-wide. Six species of the first have been recorded from British waters, of which the commonest is Antedon rosacea; four others are distinguished by having longer cirri, and do not seem to be well defined; but A. eschrichtii, a northern form, is larger, and is distinguished by having long proximal pinnules. The other genera are rare, and occur in deep water.

When we turn to survey FOSSIL CRINOIDEA, we are met with a bewildering variety of forms ranging from the Lower Cambrian to the present day. As already mentioned, there is no agreement amongst experts as to how they should be classified. Bather makes the fundamental cleavage depend on the possession of two whorls of plates in the base (Fig. 274), or of only one whorl. These two divisions he calls DICYCLICA and MONOCYCLICA respectively. He admits that in many forms allied to Dicyclica the infra-basals have disappeared; these he terms "pseudomonocyclic" forms, and believes that he is able to discriminate them from true Monocyclica.

{595}[Illustration: FIG. 274.—Crotalocrinus pulcher. × 1. B, basal; Br, arm-fan of adhering branches; col, ossicle of stem; IB, infra-basal; R, radial. (After Zittel.)]

The present author is utterly unable to believe that the Crinoidea diverged into two groups on what is a trifling point of meristic variation comparable to the varying number of rows of plates in the interradial areas of the older Echinoidea; and he is equally sceptical as to the validity of Jaekel's division of the group into CLADOCRINOIDEA and PENTACRINOIDEA, leading to the view that organs like pinnules represent totally different structures in different groups. Wachsmuth and Springer adopt as bases of classification the extent to which the arms and their branches are incorporated in the disc, and they recognise three main divisions: INADUNATA, in which the arms are completely free from the calyx; ARTICULATA, in which the arms are partly incorporated but the tegmen remains flexible; and finally CAMERATA, in which the arms and their first branches are largely incorporated in the cup; the tegmen is converted into a rigid dome and the ambulacral grooves on it become closed, as does the mouth, by the meeting of overarching folds; the grooves remaining, of course, open in the distal portions of the arms (Fig. 273). This classification, founded as it is on physiological factors, seems to the present author more satisfactory. Speaking generally, the points in which fossil Crinoids may differ from living genera are: (1) the total absence or irregular nature of the branching in the arms, so that pinnules may be said to be absent; (2) the closure of the ambulacral grooves and mouth already alluded to, and (3) the adhesion of the arms in the same ray to produce net-like structures (Crotalocrinus, Fig. 274), or a fan-shaped structure (Petalocrinus); (4) the frequent presence of two rows of brachials in one arm (biserial structure); (5) the {596}development of an enormous anal tube, so large that in extreme cases (Eucalyptocrinus) the arms may be lodged in grooves of it.

CLASS II. THECOIDEA (EDRIOASTEROIDEA, BATHER)

These remarkable Pelmatozoa are the most primitive known. They have sac-like or sometimes cushion-shaped or even disc-shaped bodies, covered with numerous irregular plates without any symmetry in their arrangement. There is no stem, but when they are fixed this is effected by an adhesion of the aboral pole. There are no arms, but on the upper surface is to be seen the impression of five ambulacral grooves radiating from a central mouth. These grooves are bordered by covering plates, which in the earliest form (Stromacystis) are seen to be slight modifications of the plates covering the upper surface of the body, but in the later genera (Fig. 275, Thecocystis) become specialised. The anus is situated on the side, as is also the madreporite. It has been suggested that Eleutherozoa were derived from this group; that individuals were occasionally overturned by the waves or currents, and in this way compelled to use their podia for locomotion. When Eleutherozoa, however, have a fixed stage in their development, they are fixed by the oral, not the aboral, surface, and hence can have no close affinity to Thecoidea. Thecoidea begin in the Middle Cambrian, but according to Jaekel impressions in the Lower Cambrian, referred to Medusae, may be casts of this group.

CLASS III. CARPOIDEA

Pelmatozoa with a well-developed stem; body bilaterally compressed; only two rays apparently developed. These are indicated only by grooves radiating from the mouth; but in {597}some cases slight horn-like outgrowths of some of the plates of the calyx may support prolongations of the grooves.

This group, which, like the foregoing, commences in the Cambrian, is perhaps more primitive than the Thecoidea in showing less influence of the water-vascular system on the skeleton; but in the presence of a differentiated stem and the development of only two rays, it is more differentiated. The anus is on one of the flat sides, covered with a flat plate acting as a valve. The members of this group were formerly confounded with Cystoidea, from which they differ in the absence of the characteristic pores. Trochocystis, the genus figured, is devoid of any horn-like outgrowths of the calyx.

CLASS IV. CYSTOIDEA

Pelmatozoa with respiratory organs in the form of "diplopores" or "pore-rhombs." In a great many cases there is a stalk, but in other cases this is atrophied, and the animal is attached by the base of the calyx. The radial canals run for a shorter or longer distance over the calyx, but the plates of the calyx themselves are not modified for them. Either they run in simple grooves, or they are protected by a special series of plates lying above the plates of the calyx. The terminal portions of the radial canals are in all cases free, supported by unbranched arms consisting usually of a double row of ossicles. These arms are termed "fingers."

It will be gathered from the description just given that the fingers and the respiratory organs distinguish Cystoidea from {598}the two foregoing classes. Formerly this class was a lumber-room in which were placed all primitive irregular Pelmatozoa. The labours of Jaekel[516] have, however, dispelled the mist which enveloped this group, and in his monograph all that can be extracted both from superficial examination and dissection of these fossils is contained. It seems possible to the present author that the class may eventually require to be divided into two, corresponding to the two main divisions which Jaekel recognises, viz. DICHOPORITA, with pectinated rhombs, and DIPLOPORITA, with diplopores.

The pore-rhombs of the Dichoporita (indicated in Fig. 277 by the small parallel lines crossing the boundaries of the plates) were, according to Jaekel, nothing but a series of folds of thin integument projecting into the interior, the outer opening of which in most cases adhered in the middle, leaving two pores connected by a groove. The inner boundaries of the folds are sometimes preserved, but in many cases they were entirely devoid of calcification, and so were lost. The radial vessels either branched a great deal, giving rise to a multitude of fingers, or, as in Echinosphaerites (Fig. 277), there were a few long fingers supporting a reduced number of radial canals. In some cases the calyx can be analysed into a regular series of cycles of plates, consisting of basals, orals, and three intervening whorls, thus including one more ring than the calyx of Crinoidea. Jaekel regards this as a primitive arrangement, believing that the irregularity seen in Echinosphaerites secondary. This is a doubtful hypothesis.

{599}The diplopores of the Diploporita appear to consist of two canals traversing the body-wall, opening close together into a common pit externally, but diverging internally. Since in some cases, as in Aristocystis (Fig. 278), this common pit is proved to have been closed externally by a very delicate layer of calcification, it is probable that the pores represent in other cases the points of origin of finger-like gills similar to those of Asteroidea. Where they were closed by calcification this was so thin and porous that the diffusion through it sufficed for respiration. Jaekel regards the Diploporita as a group derived from Dichoporita, but this seems to be extremely doubtful.

CLASS V. BLASTOIDEA

Pelmatozoa with respiratory organs in the form of longitudinal calcified folds, termed "hydrospires," radiating from the mouth. Stem well developed; calyx regular, consisting of a whorl of basals surmounted by a whorl of forked radiais, in the clefts of which lay the recumbent radial water-vascular vessels, supported each on a special plate ("lancet plate"), and giving off two rows of branches supported by short fingers (Fig. 279). Side-plates and covering plates were also developed; five orals ("deltoids") completed the calyx. The anus was at the side, just beneath one of the orals.

The hydrospires, which are the great characteristic of the class, are seen in section in Fig. 279, B (hyd). They consist of a varying number of parallel folds on each side of each "pseudambulacrum," as the lancet plate with its adhering side-plates and covering plates has been termed. In the most primitive genus, Codaster, they appear to have opened directly to the exterior, and to have been placed at right angles to the lines of union of the radial and oral plates, just like the grooves of a pectinated rhomb. In more modified forms, such as Pentremites and Granatocrinus (Fig. 279), the outer openings were overarched {600}by the extension of the side-plates of the radial vessel, and the whole group of folds has a common opening near the mouth; indeed, in the highest form there is one common "spiracle" for the two groups of folds in an interradius, which in one interradius is confluent with the anus. The hydrospires, when they reach this form, irresistibly recall the genital bursae of Ophiuroidea (Fig. 214, p. 490), and very possibly served the same purpose.

Reviewing the whole group of the Pelmatozoa, we see that in the Cambrian they begin with the extremely primitive Thecoidea and Carpoidea, together with some obscure forms which, combining a stem with pentamerous symmetry in the calyx, are supposed to be the forerunners of the Crinoidea. In the Lower Silurian or Ordovician the two groups of the Cystoidea make their appearance, possibly independently developed from either Carpoidea or primitive Crinoidea, which in this period are present in unmistakable form. In the Upper Silurian the Blastoidea appear, distinguishable from the most regular Cystoidea only by their hydrospires. It seems practically certain that they were developed from Cystoidea, and we follow Jaekel in believing that they arose from Dichoporita. The Carpoidea do not extend beyond the Ordovician, and by the end of the Carboniferous period Cystoidea and Blastoidea die out, leaving only the Crinoidea, which at that period were at their maximum development. From the Carboniferous to the present day the Crinoidea have continually decreased, leaving in recent seas, as sole representatives of the Pelmatozoa, only the few forms described at the beginning of this chapter.

{601}CHAPTER XXI

ECHINODERMATA (CONTINUED): DEVELOPMENT AND PHYLOGENY

In Chapter XVI. it was stated that whilst a more or less perfectly developed radial symmetry was one of the characteristic features of the phylum Echinodermata when in the adult condition, yet in the immature or larval condition the members of the group have a strongly marked bilateral symmetry. In this feature larval Echinodermata resemble the other Phyla of the animal kingdom which have a well-developed coelom, such as Annelida, Mollusca, Vertebrata, etc. Since, then, the peculiar radial symmetry is gradually acquired during the growth of the Echinoderm, we may possibly discover by a close scrutiny of the life-history what is the nature and meaning of this departure from the ordinary type of structure among coelomate animals.

There are two kinds of development met with amongst Echinodermata, which may be roughly characterised as the "embryonic" and the "larval" type respectively, although neither description is exact. In developmental histories of the first type so much reserve material is laid up in the egg in the form of food-yolk that the young animal whilst in the bilateral stage requires little or no food. In some cases, however, as in Amphiura squamata, the mother pours out a nourishing exudation; but whether this is so or not, the parent in nearly every case carries the young about with her until they have reached the adult condition. In some Asteroidea, as for instance in the Antarctic species Asterias spirabilis (Fig. 280), the young become fixed to the everted lips of the mother; in Amphiura squamata, and some other Ophiuroidea the eggs remain in the genital bursae, which serve as nurseries; in some Spatangoidea, {602}as for instance in Hemiaster philippi (Figs. 250, 281), the eggs are carried in some of the deeply grooved petaloid ambulacra; whilst in Holothuroidea they may develop in the body-cavity (Phyllophorus urna), or they may adhere to the back of the mother (Cucumaria crocea, Fig. 259, p. 573), or they may be protected in special brood-pouches either on the ventral side of the parent (Cucumaria laevigata) or on the dorsal surface (Psolus ephippifer, Fig. 261).

The majority of these cases of embryonic development have been recorded from Arctic or Antarctic waters; it appears as if conditions there were not favourable to the larval type of development. In Pelmatozoa the development of Antedon rosacea alone is known, and that is of the embryonic type.

So far, however, as their mode of propagation is known, it may confidently be affirmed that the development of the majority of the species of Eleutherozoa is of the second or larval type. In this type there is little food-yolk in the egg, and the young animal or larva is forced from a very early period of development to seek its own living, and hence it is usually a considerable time (from a fortnight to two months) before the adult form is attained. When the embryos of different groups of Eleutherozoa are compared, there is no obvious agreement in structure between them; but the larvae of the four classes of Eleutherozoa exhibit with differences in detail a most remarkable fundamental similarity in type, and we are accordingly justified in regarding the larval development as primitive, and the embryonic type as derived from it and differently modified in each case.

{603}[Illustration: FIG. 281.—Hemiaster philippi. Enlarged view of a single petal, showing the embryos in situ. (From Wyville Thomson.) The whole animal is shown in Fig. 250, p. 555.]

In the typical larval development the eggs are fertilised after being laid, and they then undergo segmentation into a number of equal, or nearly equal, segments or "blastomeres." These arrange themselves in the form of a hollow sphere or "blastula," the cavity of which is called the "blastocoel" and afterwards becomes the primary body-cavity of the larva. This cavity contains an albuminous fluid, at the expense of which development appears to be carried on (Fig. 282, B). The cells forming the blastula acquire cilia, and the embryo begins to rotate within the egg-membrane, which it soon bursts, and, rising to the surface of the sea, begins its larval life. The blastula is therefore the first well-marked larval stage, and it is found in a more or less recognisable form in life-histories of members of every large group in the animal kingdom. Only in the case of Echinodermata and of forms still lower in the scale, however, does it appear as a larval stage. The free-swimming blastula stage is reached in from twelve to twenty-four hours. Soon the spherical form of the blastula is lost; one side becomes flattened and thickened, owing to a multiplication of cells, so that they become taller and narrower in shape. Shortly afterwards this thickened plate becomes buckled inwards, encroaching on the cavity of the blastocoel. The larva has now reached the second stage of its development; it has become a "gastrula" (Fig. 282, C). The plate of thickened cells has become {604}converted into a tube called the "archenteron" (Fig. 282, C, arch), which is the rudiment of both the alimentary canal and the coelom of the adult. This tube communicates with the exterior, in virtue of its mode of formation, by a single opening which is called the "blastopore," which becomes the anus of the later larva and adult. Whilst the gastrula stage is being acquired, the blastocoel or primary body-cavity is invaded by wandering cells budded from the wall of the archenteron (Fig. 282, A, B, C, mes). These cells, which are called "mesenchyme," are the formative cells of the skeleton, connective tissue, and wandering cells of the adult. When the larva has a skeleton they are formed very early, arising in the young blastula stage (Ophiuroidea) or in the stage immediately before the formation of the archenteron (Echinoidea, Fig. 282, A, B) and secreting the skeleton. When the larva is devoid of a skeleton (Asteroidea and Holothuroidea), the mesenchyme usually does not appear till the gastrula is fully formed.

The gastrula stage is reached in twenty to thirty-six hours. Then one side of the larva becomes concave, and the cilia become restricted to a thick band surrounding this area. In this way is formed the rudiment of the longitudinal band of cilia, which is the organ of locomotion throughout the larval life. At the apex of the archenteron a thin-walled vesicle is formed, which soon becomes divided off from the rest. This vesicle, which almost immediately divides into two sacs, right and left, is the {605}rudiment of the "coelom" or secondary body-cavity of the larva; the remainder of the archenteron forms the definitive gut, and becomes divided by constriction into an oesophagus, a stomach, and an intestine, and at the same time bent into a shallower or deeper V-shape, the concavity of which is towards the concave side of the body. Within this area of the surface a new funnel-shaped depression makes its appearance. This is the "stomodaeum," the rudiment of the mouth of the larva, and it soon joins the apex of the larval oesophagus; the conjoined tubes henceforth bearing the name oesophagus since the ectodermal and endodermal parts become indistinguishably fused. Along the sides and floor of the oesophagus is formed a V-shaped ridge bearing strong cilia; this is the "adoral band of cilia" which sweeps the food (consisting of Diatoms, Infusoria, etc.) into the mouth. The larva is now known as a Dipleurula and appears in four modifications, each characteristic of a Class of Eleutherozoa. These differ from one another principally in the following points:—(a) The folding of the ciliated band; (b) the divisions of the coelomic sacs; (c) the development and fate of the praeoral lobe (i.e. the part of the body in front of the mouth); (d) the fate of the larval mouth. The types of Dipleurula are as follows:—

(1) The Bipinnaria, the larva of Asteroidea. In this type there is a very long prae-oral lobe. The ciliated band runs along its edges, and is produced into a backwardly directed loop on its under surface. This loop soon becomes separated from the rest of the band as a distinct prae-oral loop, the rest forming a post-oral loop. Both loops are drawn {606}out into short tag-like processes, in which we may distinguish (following Mortensen's[517] notation) in the prae-oral loop an anterior median process (Fig. 283, a.c.o.b), and a pair of prae-oral processes (a.v.a). In the post-oral loop there is a median dorsal process (p.c.o.b) and paired anterior dorsal (a.d.a), posterior dorsal (p.d.a), posterior lateral (p.l.a), and post-oral (p.v.a) processes. At the apex of the prae-oral lobe between prae-oral and post-oral ciliated rings there is an ectodermic thickening, recalling the so-called apical plate of Annelid larvae.

(2) The Ophiopluteus, the larva of the Ophiuroidea. In this type the prae-oral lobe remains small, and the primitive ciliated band is undivided. The processes into which it is drawn out are very long, and are supported by calcareous rods. Of these processes we may distinguish prae-oral, postero-dorsal, postero-lateral, and post-oral. The postero-lateral are always much longer than the rest, so that the larva when swimming appears to the naked eye as a tiny V. In the case of Ophiothrix fragilis (Fig. 284, A) the postero-lateral processes are many times longer than the rest of the body. The Ophiopluteus was the first Echinoderm larva to be recognised. It was discovered by Johannes Müller,[518] who also discovered the other three types of {607}Dipleurula. He named this one Pluteus (easel), from a fancied resemblance, when turned upside down, to a painter's easel. The same name was bestowed on the next type, to which it presents a superficial resemblance, and hence the distinguishing prefix "Ophio-" was added to the original name by Mortensen.

(3) The Echinopluteus, the larva of the Echinoidea. This type is strikingly like the preceding one in possessing a very small prae-oral lobe and in having the processes of the ciliated ring supported by calcareous rods, but a close inspection of these shows that they do not exactly correspond to those of the Ophiopluteus. Thus we have prae-oral, postero-dorsal, and post-oral processes (Fig. 285), but usually no postero-lateral process, and when it does occur it remains short. On the other hand, an antero-lateral process unrepresented in the Ophiopluteus is constantly present, and in its later stage the Echinopluteus develops, out of parts of the ciliated ring, horizontally-placed crescentic ridges of cilia, which are termed ciliated epaulettes (Fig. 285, a.cil.ep). There may even be, as in the larva of Echinus esculentus, a second posterior set of these (Fig. 285, p.cil.ep). In the older larva at the apex of the prae-oral lobe there is an ectodermic thickening, at the base of which are developed nerve-cells and nerve fibres constituting a larval brain (Fig. 285, ap).

(4) The Auricularia, the larva of the Holothuroidea. This type strikingly resembles the Bipinnaria in its external features. The prae-oral lobe is well developed, and has on its under surface a backwardly projecting loop of the ciliated band, which is not, {608}however, as in the Bipinnaria, separated from the rest of the band. The processes of the band are much more faintly marked than in the Bipinnaria, the anterior median, prae-oral, and median dorsal processes being absent; but a pair of intermediate dorsal processes are developed in the interspace between anterior and posterior dorsal.

In the Bipinnaria, Ophiopluteus, and Echinopluteus the coelomic vesicle, after separation from the archenteron, divides into right and left halves. The left then sends out a short dorsal process, which, fusing with the ectoderm, acquires an opening to the exterior. This opening is the primary madreporic pore, and the process of the left coelomic sac, which is ciliated, is the pore-canal. In the Auricularia the pore and pore-canal are formed before the division of the coelom. In the Bipinnaria the right and left sacs subsequently fuse in the front part of the prae-oral lobe. In the first three types of larva the coelomic sac on each side then undergoes a segmentation into anterior and posterior portions. At the hinder end of the anterior sac on each side a swelling occurs. That on the left side is the "hydrocoel," or rudiment of the water-vascular system (Fig. 287, A^3, l.hy); it {609}quickly assumes a crescentic form, and gives off five blunt outgrowths, which are the rudiments of the radial canals, and the terminal tentacles. It remains in connexion with the anterior coelom by a narrow neck, which later becomes the stone-canal. That on the right side separates completely from the right anterior coelom; it remains small, and forms the madreporic vesicle (Fig. 287, A^3, r.hy) of the adult. In the Ophiopluteus and in the larva of Asterina gibbosa (v. infra) it occasionally takes on a form similar to that of the hydrocoel; from which circumstance, as well as from the similarity in its mode of origin, it is here regarded as a right hydrocoel, i.e. a rudimentary fellow of the organ which develops into the water-vascular system.

In Auricularia (Fig. 287, D) the coelomic vesicle, after the pore-canal is formed, divides into an anterior and a posterior half. The posterior part then divides into right and left halves, {610}whilst the anterior sac divides into dorsal and ventral halves, connected by a narrow neck. The ventral half soon assumes the familiar feature of the hydrocoel (Fig. 287, D^3, l.hy), whilst the dorsal half forms an insignificant swelling on the course of the conjoined stone- and pore-canals, which represents the left anterior coelom of the other types; neither right anterior coelom nor right hydrocoel being developed. The neck of communication between dorsal and ventral halves is, of course, the stone-canal.

The Dipleurula larva leads a free-swimming life for a period varying from two weeks to two months, and then undergoes METAMORPHOSIS into the adult form. The details of this process have been worked out in comparatively few cases; and the species in which they are most thoroughly known is the Asteroid Asterina gibbosa. The development of this species is intermediate in character between the embryonic and larval types. The eggs are larger than is usual among Asteroidea, and are filled with a bright orange yolk. The larva differs from the Bipinnaria in the absence of the characteristic ciliated bands and in the very early occlusion of the anus. There is, however, a band of cilia round the edge of the prae-oral lobe, which corresponds to portions of the prae-oral and post-oral bands combined of the Bipinnaria.[519]

The larva has a form which may be described as boot-shaped (Figs. 288, 289). The sole of the boot is the great prae-oral lobe, behind which is the mouth. The larva takes little or no food, and completes its metamorphosis in ten to twelve days. It does not swim at the surface, but creeps slowly over the bottom by the aid of the ciliated band mentioned above, while it can also attach itself, using the edges of the prae-oral lobe as a sucker.

After leading an existence of this kind for seven or eight days it fixes itself permanently by a disc-like prominence, which appears on the anterior surface of the prae-oral lobe within the area surrounded by the thickened rim which, as explained above, forms a margin to the prae-oral lobe. The larva then becomes divided by a constriction into a disc and a stalk, and the former is gradually converted into the body of the young Starfish, whilst {611}the latter continually diminishes in size, and eventually entirely disappears, when the young Starfish commences to walk about on its podia. The disc becomes bent downwards and to the left, so as to make nearly a right angle with the stalk, and the last vestige of the latter springs from the peristome of the Starfish inside the water-vascular ring (Figs. 289, B, C).

The form of the Starfish is attained principally by the preponderant growth of the left hydrocoel and of the left posterior coelom. Both these sacs take on the form of hoops, which, by the meeting of their ends, are converted into rings. The hydrocoel has already grown out into five lobes, which are the rudiments of the radial water-vascular canals, and the tips of which become the terminal sensory tentacles (Figs. 288, 289, 1-5); but now the left posterior coelom grows out into five lobes also, forming a parallel but outer ring. These lobes (Figs. 288, 289, I.-V.) are the rudiments of the arms, which are at first quite independent of those of the radial canals, but gradually, when the larva has attained the age of nine days (Fig. 289, B, C), they become applied to the outgrowths of the hydrocoel. These by this time have developed each two pairs of branches, the rudiments of the first two pairs of tube-feet in each radius. The larval mouth vanishes, and a new mouth is formed on the left side in the centre of the hydrocoel ring, when the metamorphosis is complete. The adult anus is {612}formed about the same time. The primary pore-canal in Asterina as in all Dipleurulae opens into the anterior coelom; the stone-canal is formed from a ciliated groove running along the neck of communication between this and the hydrocoel. The constriction dividing the body into disc and stalk divides the anterior coelom (single in Asterina as in the older Bipinnaria) into two parts; the portion included in the disc forms the axial sinus of the adult. The lower end of the axial sinus expands and surrounds the adult mouth, forming the inner perihaemal ring; the outer perihaemal ring is formed by the juxtaposition of four wedge-shaped outgrowths from the left posterior coelom and one from the anterior coelom. From these the radial perihaemal canals subsequently grow out into the arms. The metamorphosis of Bipinnaria has been well worked out by Goto,[520] and it agrees in essential features with that of Asterina gibbosa; in fact, the differences which Goto maintains between the two types may be reasonably explained on the supposition of some stages having escaped the notice of this observer. The larva develops on the apex of the prae-oral lobe three papillae for occasional attachment,[521] and in the centre of these a cup-shaped disc for permanent fixation when the prae-oral lobe is converted into a stalk. When these papillae (Fig. 290, fix) have been developed the larva is known as a Brachiolaria.

{613}[Illustration: FIG. 290.—Brachiolaria fixing itself, × 60. Ast, rudiment of the body of the Starfish; fix, fixing processes. (After Johannes Müller.)]

The metamorphoses of the other types of Dipleurula contain no fixed stage. They are what might be called "cataclysmal metamorphoses." That is to say, the outer form and habits of the larva are preserved till the last moment, whilst the organs of the adult are being gradually perfected; then in an hour or two all trace of larval structures disappears. The Ophiopluteus preserves the larval mouth, round which the hydrocoel grows; the long lateral ciliated processes are preserved till the animal has attained all the adult characters. Before this, however, it passes through what may be called an "Asteroid" stage in development, in which the ambulacral grooves are open. The Echinopluteus loses both larval mouth and anus. It develops the adult organs on the floor of a sac-like invagination of the ectoderm, situated on the left side within a loop of the ciliated band (Fig. 291, B, C). This invagination becomes completely closed. It is termed the "amniotic cavity," and its roof is termed the "amnion." On its floor are developed the primary tentacles, terminating the radial canals, as well as a number of spines. After taking on a creeping life and losing its larval appendages, the young Sea-urchin passes through an "Asteroid" condition, in which the arched dorsal surface, the future periproct, is greater in extent than the ventral, and the radial canals run horizontally out from the water-vascular ring and terminate in free movable podia (Fig. 291, C and D, pod), ending in suckers, in the centre of which are pointed sense-organs. These {614}podia become later enclosed in grooves in the corona, and are reduced to vestiges in the adult.

The Auricularia is the only type of Dipleurula in which larval mouth and anus are retained. For this reason it has been supposed that its median plane of symmetry remains the median plane of the adult. The researches of Bury[522] have shown that this is not so. As in other types of Dipleurula (with the possible exception of the Ophiopluteus) the adult position of the {615}mouth is on the left side of the larva, and in the commencement of the metamorphosis the mouth migrates into this position (Fig. 286, C). Then the rudimentary prae-oral lobe is rapidly absorbed, so that the mouth again acquires a terminal position. The hydrocoel (Fig. 286, A, hy) has by this time completely encircled the oesophagus, and from it grow out the radial canals which bud off the feelers[523] (buccal tentacles) into the larval stomodaeum. This, although it later flattens out to form the adult peristome, forms in these stages an almost closed sac, reminding us of the amniotic cavity in the Echinopluteus. The ciliated band breaks up into a number of pieces, which rearrange themselves so as to form a series of transverse rings of cilia; so that the free-swimming life can be carried on somewhat longer. The animal in this stage is called a "pupa" (Fig. 292); it eventually loses the rings, drops to the bottom, and develops tube-feet. From specimens which the author has seen, he has little doubt that in some cases the young animal passes through an "Echinoid" stage, for it possesses, besides the feelers, only median tube-feet, terminating the radial canals, and it is covered by a cuirass of plates, which recalls the Echinoid corona.[524]

Reviewing the development of the Eleutherozoa in the light of the facts so far presented, and using the same method of reasoning which is employed in the case of other groups of animals, we seem to be justified in concluding that the Echinodermata are descended from a simple free-swimming ancestor possessing the fundamental characters of the Dipleurula. These would include a longitudinal folded band of cilia as the principal organ of locomotion; a thickened plate of nervous epithelium at {616}the anterior end serving as combined sense-organ and brain; a V-shaped band of cilia projecting into the oesophagus as the organ of nutrition; a wide, shallow stomodaeum and an alimentary canal consisting of three well-marked divisions, viz. oesophagus, stomach, and intestine; and finally a secondary body-cavity or coelom, consisting of three divisions on each side, though possibly the most anterior pair were confluent in the prae-oral lobe. On the left side the anterior coelom opened to the exterior by a short ciliated canal. To the hypothetical group so defined which were certainly not Echinodermata the name PROTOCOELOMATA may be given.

Now amongst the lowest types of animal in which traces of Vertebrate structure can be detected, there is one group, the HEMICHORDATA (Vol. VII. p. 3), in which there is a larva which strikingly recalls the Dipleurula. This larval form belongs to Balanoglossus and is called the Tornaria. It possesses a well-marked prae-oral lobe and a folded longitudinal ciliated band, which resembles that of Auricularia. Its peculiarity is that in addition there is a posterior ring of cilia (Fig. 293, p). The coelom is in five divisions:—a median anterior sac (a.c) opening to the exterior by a short ciliated canal on the left side; and paired middle divisions (m.c) and posterior divisions (p.c). At the apex of the prae-oral lobe there is a plate consisting of sensory epithelium, with nerve-fibres at its base, which acts as a brain. Tornaria undergoes metamorphosis, assumes a worm-like form, and takes on a burrowing life. The five divisions of {617}the coelom are retained, and it can be proved that the pore-canal, like the madreporite of Echinodermata, is used for taking in water. Further, there are two aberrant sessile members of the group (Cephalodiscus and Rhabdopleura), in which the middle divisions of the coelom which would correspond to the hydrocoels are produced into long arms, each with a double row of ciliated tentacles, which strikingly recall the radial canals and podia of the Pelmatozoa. Taking all these facts into consideration, it seems probable that Vertebrata and Echinodermata both arose from PROTOCOELOMATA.

When we turn to the developmental history of Echinodermata for light on the question as to how the bilaterally symmetrical ancestor became converted into the radially symmetrical Echinoderm, it seems probable that only in the development of the Asteroidea can we hope to find the solution of the problem. The abrupt changes of habits shown in the metamorphoses of the other types are clearly secondary phenomena. No species of animal could suddenly change its habits from swimming by means of cilia to walking with tube-feet. In the development, however, of Asterina gibbosa we get a hint of the way in which a free-swimming life could alternate with periods of temporary fixation, gradually passing into a condition in which the fixation was permanent. This period in the history of the race when ancestral Echinodermata were sessile would mark the point at which Eleutherozoa diverged from Pelmatozoa, and the former existence of a fixed ancestor explains the tendency first to asymmetry and later to radial symmetry. Bilateral symmetry is characteristic of most free-swimming animals which have to pursue a straight course through the water, but in fixed forms no disadvantage arises from want of symmetry. A radial disposition of organs is, however, valuable to them, since food must be sought and danger avoided from all points of the compass; and hence we can understand, when fixation became permanent, how one hydrocoel could grow larger than the other, and finally assume the form of a ring.

The last question which arises is the vexed one of the mutual relationships of the various Classes constituting the Phylum. Before attempting to seek for light on this problem from development, it will be necessary to sketch the life-history of Antedon rosacea, the only Pelmatozoon whose development is known.

{618}[Illustration: FIG. 294.—Three views of the development of Antedon rosacea. A, free-swimming larva; B, longitudinal section of free-swimming larva; C, oral view of young fixed form. a.c, Anterior coelom; amb, ambulacral groove; ap, apical plate of sensory and nervous tissue; cil, ciliated ring; hy, hydrocoel; l.p.c, left posterior coelom; mad, primary pore-canal; pod, podia; r.p.c, right posterior coelom; stom, larval stomodaeum. (A and B after Bury; C after Perrier.)]

The eggs are comparatively large and full of food-yolk, and they adhere for a considerable period to the pinnules. They pass through a large portion of the development within the egg-membrane. The blastula and gastrula are formed in the usual way, but the formation of the coelom is most remarkable (Fig. 287, E^1, E^2). The archenteron divides into anterior and posterior divisions. The posterior divides into right and left, posterior coelomic sacs, but before the division is complete a dorsal and a ventral tongue grow out from the anterior division and unite posteriorly, encircling the band of connexion between right and left posterior coelomic sacs like a ring. This band of connexion becomes solid and is absorbed, and pari passu the ring becomes converted, by the disappearance of its central opening, into a sac, which is the definitive gut (Fig. 287, E). The rest of the {619}anterior division divides into a thick-walled sac, the hydrocoel, on the left, and a median thin-walled anterior coelom, which sends a long extension into the anterior portion of the larva, which we may compare to the prae-oral lobe of the Bipinnaria. The anterior coelom communicates with the exterior by a short pore-canal, and later forms a connexion, the stone-canal, with the hydrocoel. At the apex of the prae-oral lobe there is formed a thickened patch of ectoderm, bearing stiff sensory hairs, and having at their bases nerve-fibres and ganglion cells. This larval brain corresponds to that of the Tornaria and Echinopluteus. Behind the brain there is a glandular pit, which is used for fixation, and recalls the similar organ in the Bipinnaria. A series of ciliated rings is then formed, and between the second and third of them an oval depression appears. This is the stomodaeum; but as the larva takes no food it does not communicate with the gut (Fig. 295, A, stom).

The larva next escapes from the egg-membrane and swims freely for a day or two, and then, like the Bipinnaria, fixes itself by the apex of the prae-oral lobe, which is converted into a stalk. The larval stomodaeum closes, and the oesophagus of the adult appears as a solid peg of cells abutting against it; round this peg the hydrocoel grows like a ring.

The closed stomodaeum and the underlying hydrocoel are now rotated backwards until they come to be at the end of the animal opposite the stalk (Fig. 295, C). The left posterior coelom, which has also, as in the Asteroid larva, assumed a hoop-like form, is carried along with them; but the right posterior coelom becomes shifted forwards and sends out five outgrowths into the stalk, which form the rudiments of the chambered organ, and a central one as a continuation of the genital stolon (Fig. 295, D, gen.st), the extension of the anterior coelom (Fig. 294, B) having disappeared.

Then the outer wall of the stomodaeum splits into five valves—the future oral valves. The radial canals appear as freely projecting tentacles, which issue in the intervals of these valves and soon acquire two pairs of lateral branches. The skeleton consists of five oral plates in the oral valves, of a ring of five basals, of three small under-basals, and of a series of "columnals," i.e. stem-ossicles, as rings embracing the stalk. The area of attachment is supported by a "foot-plate." The radial {620}plates next appear as a ring of small ossicles between the orals and basals, and simultaneously the arms make their appearance as five outgrowths supported by the first radials, and by the other radials when these appear. The free radial canals now become adherent to the arms, but these canals soon give off paired branches of unlimited growth, which are supported by bifurcations of the primitive arms, and in this way the ten arms of the adult are established. So far, then, as the water-vascular system is concerned, the apparent forking is not a true dichotomy, but results from the production of two opposite branches, whilst the main axis ceases to grow. The appearance of cirri marks the fusion of the uppermost stem-ossicles to form a centro-dorsal, and shortly afterwards the young Antedon snaps off its stem and swims away.

Now in reviewing this life-history we cannot fail to be struck with resemblances to the development of Asteroidea, and especially to that of Asterina gibbosa. The absence of a connexion between stomodaeum and gut is due to the embryonic mode of life. On the other hand, the presence of a long prae-oral lobe, containing an extension of the anterior coelom and having a fixing organ at its apex, can only be paralleled among Asteroidea. In broad outlines, then, up to the period of fixation the two developments are parallel, but after this point a {621}divergence takes place, which points clearly to the splitting of the Echinoderm stem into two main branches, corresponding with two different sets of habits. In the Eleutherozoan stock, represented by the development of the Asteroidea, the disc became flexed ventrally on the stalk, so that the mouth and podia were brought within reach of material drifting along the bottom, which the podia were employed to seize. As a consequence the base of the stalk was brought near the mouth, and so it came about that the hydrocoel, when it became a ring, encircled both. In the Pelmatozoan stock, on the other hand, the podia and mouth are rotated upwards and backwards from the stalk, which thus came to have an aboral position (Fig. 296, B). The podia are thus placed in a favourable position for capturing free-swimming organisms, which their cilia sweep toward them. It is worthy of note that a similar change of position of the mouth occurs in other groups of animals which have similar habits (Polyzoa Entoprocta, Tunicata).

The division therefore of the phylum must have occurred at an extremely remote epoch, before the hydrocoel was a closed ring, and before, therefore, radial symmetry was completely attained.

Turning now to the question of the origin of the classes of Eleutherozoa, we find that the study of development strongly reinforces the views gained from the study of adult anatomy. The Asteroidea are the most primitive group; only in their case {622}is the fixed stage retained, and both Ophiuroidea and Echinoidea pass through an Asteroid stage in development. The only serious competitors for the position are the Holothuroidea, which many have imagined to have been directly derived from Cystoidea (in the old sense; better Thecoidea). This view, though adopted by Semon,[525] Haeckel,[526] and Bather,[527] is open to many objections. The type of Holothuroid development referred to in these discussions is that of the extremely aberrant Synapta digitata, in which the radial canals are vestigial structures which disappear in the adult. In this species, where the feelers are multiplied, some originate in the larva directly from the water-vascular ring, and thus alternate with the canals. From this circumstance Semon drew the conclusion that the radial canals of Holothuroidea are not homologous with those of other Echinoderms, but this conclusion is contradicted by the development of more normal species, in which all the feelers spring from the radial canals. The meridional course of these canals, the closure of the ambulacral grooves, coupled with the retention of a nervous ectoderm, are all features found in Echinoidea. So is also a reduction in the number of the genital organs, on which Bell[528] laid such stress that he separated Holothuroidea from all other Echinoderms. But if in Spatangoidea a reduction to four and even three can take place (Fig. 246, p. 552), why should a reduction to two or one excite surprise? The primitive outer appearance of the Auricularia is counterbalanced by the development of the coelom, which is much modified, so that the primitive bilateral arrangement is obscured. If, then, Asteroidea are the most primitive Eleutherozoa, we may imagine that primitive Echinoidea were derived from Asteroidea through adaptation to life in crevices, where an upward bending of the radii was of advantage, in order to enable the animal to attach its podia above as well as below itself; and that Holothuroidea arose from primitive Echinoidea in which the plates of the corona were still movable, through a further adaptation to narrow crevices, where worm-like wriggling would be the most successful method of adapting themselves to their environment.

{623}The final result, then, of all our inquiries leads us to a view of the mutual affinities of the classes of Echinoderms, which may be indicated in the following table:—

Protocoelomata | First fixed ancestor / \ Asteroidea Protopelmatozoa (Thecoidea?) / \ \ Ophiuroidea Protechinoidea \ / \ Carpoidea Echinoidea Holothuroidea / \ / \ Cystoidea \ / Crinoidea Blastoidea

We shall hazard the prophecy that if ever pre-Cambrian Echinoderms are found, there will be amongst them small stalked forms which may be superficially classed with "Cystids," but which are in reality the fixed ancestors of Asteroidea. They should have an irregular skeleton, and be devoid of arms, which are secondary formations; but they should indicate, by the proximity of the mouth to the stalk and by the relation to the stalk of the grooves for the podia, that they have diverged from the Pelmatozoan stock, and are the ancestors of Eleutherozoa.

INDEX

Every reference is to the page: words in italics are names of genera or species; figures in italics indicate that the reference relates to systematic position; figures in thick type refer to an illustration; f. = and in following page or pages; n. = note.

Abbott, 422 Abdomen (= third chamber of Monaxonic Radiolarian shell), 84 Abdominal cirrhi, 139 f. Aboral, blood-ring, of Asterias rubens, 452; of Ophiothrix fragilis, 490; of Echinus esculentus, 529; coelom, of Antedon rosacea, 585; nervous system, of Antedon rosacea, 584; sinus, of Asterias rubens, 449; of Ophiothrix fragilis, 490; of Echinus esculentus, 528, 529 Abortive nuclei, of Myxosporidiaceae, 107 Abyla, 307 Abylinae, 307 Abyssal, Radiolaria, 76; Sponges, 239 f. Acamptogorgia, 356 Acanella, 353; A. simplex, 353 Acantharia (Actipylaea), 76, 78, 78, 80; myophrisks in, 80; Zooxanthella in, 80; reproduction of, 86 n.; skeleton of, 82 Acanthaster, 458, 462 Acanthin, 71 n., 75, 76 Acanthocephala, nutrition of, 38 Acanthoconia barrandei, 207, 207 Acanthocystis, 71; budding of, 73; habitat, 75 Acanthogorgia, 355 Acanthometrids (= Acantharia, q.v.), parasitic Amoebophrya in, 161 Acanthonida, 78 Acanthotrochus, 577 Acarnus, 223 Accumulative anabolism, growth, 9, 13, 15 f.; in relation to brood-formation, 32 f. Acephalinidae, 97 Acineta, 159, 160 Acinetina = Suctoria, 158 f. Acontia, 369 Acrasieae, 90 f. Acrophytum, 333, 349 Actine, 183 Actinelida, 78 Actinia, 381; A. cari, 378; A. equina, sense organ of larva of, 373; A. mesembryanthemum, 379, 381; longevity of, 375 Actiniaria, 377 f.; viviparity of, 373; symbiosis of, 377; colours of, 379 Actiniidae, 381 Actiniina, 380 Actinobolus, 137; tentacles and trichocysts of, 152 Actinocrinus, 594 Actinodendron, 384; A. arboreum, 384; A. glomeratum, 366; A. plumosum, 366, 384 Actinoloba (= Metridium), 371, 372, 381; A. dianthus, 379, 381; A. marginata, 378 Actinolophus, 70; habitat of, 75 Actinometra, 588, 589, 594 Actinomma, 77; A. asteracanthion, skeleton of, 77 Actinomonas, 70, 73, 75 n. Actinomyxidiaceae, 98 Actinophrys, 70 f., 96 n.; A. sol, 71; habitat of, 75 Actinopoda, 570 Actinosphaerium, 70, 72 f.; endogamy of, 73 f., 75; regeneration of, 35; A. eichornii, 72 Actinostola (usually placed in Hertwig's family Paractidae, allied to Bunodidae, 382), 379 Actinotryx, 371, 383; A. mussoides, 383 Actinozoa = Anthozoa, 326 f. Actipylaea (= Acantharia), 76 Actissa, 77, 83 Acystosporidae, 97, 102 f.; active zygote of, 34 Adambulacral, ossicle, of Asterias rubens, 434; of Ophiothrix fragilis, 479; of Asteroidea compared to covering-plates of Crinoidea, 589; spine, of Asterias rubens, 434 Adamsia, 377; A. palliata, 378, 381; A. rondeletii, 378 Adaptation to fresh water, 176 f. Adelea ovata, syngamy of, 101 Adelocodonic, 265 Adhesion of species, 174 n. Adinidae, 130 n. Adoral, band of cilia in Dipleurula larva, 605; membranellae, 145; trichocysts, 145; wreath, 137 f.; wreath of Vorticella, 156, 157 Aegina, 296 Aeginidae, 296 Aeginopsis, 296 Aeolis, nematocysts of, 248 Aequorea, 278 Aequoreidae, 278 Aerotaxy, 23 Aethalium septicum (= Fuligo varians), 92 f. Afferent canal of contractile vacuole, of Stylonychia, 139, 140; of Stentor, 156 Africa, Tropical, antimalarial measures in, 106; Trypanosomic diseases of, 120 f. Agalma, 300, 307 Agalminae, 307 Agaricia, 403 Agaricoides, 350 Agassiz, 258, 312, 319; on classification of Endocyclica, 533; of Clypeastroidea, 548 Aggregate, formation, in Microgromia, 59; social, of Vorticella, 158; (rosette) of Treponema, 120 Aggregation of plasmodia into aethalium, 92 f. Agitation, stimulus of, 19 f. Aglaophenia, 276, 279 Aglaophenopsis (Plumulariidae, 279), 277 Aglaura, 294 Aglauridae, 294 Aiptasia couchii, 382 Air, presence of Flagellate spores in dust of, 118 Air-borne germs in relation to putrefaction, etc., 43 Alate, 185 Alcock, 268 Alcyonacea, 346 f. Alcyonaria, 329 f., 340; colour, 337; dimorphism, 333; food, 339; mesenteric filaments, 333; nematocysts, 247; phosphorescence, 338; reproduction, 340; skeleton, 334; spicules, 334; zooids, 330 Alcyoniidae, 349 Alcyonium, 330 f., 332, 349; nematocyst of, 247; A. digitatum, 332, 338 f., 347, 349; larva, 341; A. glomeratum, 349; A. palmatum, 340; A. purpureum, 338 Aleurone, 37 Algae, related to holophytic colonial Flagellata, 109, 130 Algeria, dourine disease in, 119 Alicia mirabilis, 382 Aliciidae, 382 Alimentary canal, of Asterias rubens, 438; of Ophiothrix fragilis, 485; of Echinus esculentus, 516; of Echinarachnius parma, 546 f.; of Echinocardium cordatum, 551; of Antedon rosacea, 583; of Hyocrinus, 589; of Actinometra, 589; development of, in Eleutherozoa, 604, 605; in Antedon rosacea, 618, 619 Allen, on food of Echinus esculentus in Plymouth Sound, 516 Allman, 246, 265, 267, 273, 274; on Cystoflagellates, 135 Allogromia, 59 f., 65 Allogromidiaceae, 58; habitat of, 48, 59 Allopora, 287; A. nobilis, 287 Alpheus, 351 Alternating modes of brood-formation in Sporozoa, 48 Alveolar, structure (fine) of cytoplasm, 6; system (coarse) in relation to skeleton of Radiolaria, Dreyer's scheme of, 84 Alveolate ectoplasm, of pelagic Foraminifera, 61; of Heliozoa, 71 f.; of Actinosphaerium, 72 f.; of Radiolaria, 79; pedicellaria of Leptogonaster, 456 Alveole (= minute cavity in cytoplasm), 5 f.; in Ciliata, 142; in Stylonychia, 140; (= large vacuole of Radiolaria, etc.), 76, 79, 84 Alveolina, 59 Alveolus, of Echinus esculentus, 526 Alveopora, 397 Amalthea (Fam. Corymorphidae, 273), 266 Ambulacral area, of Echinarachnius parma, 544; of Echinocardium cordatum, 550 Ambulacral groove, of Asteroidea, 432; representative in Ophiuroidea, 481; representative in Echinoidea, 515; of Pelmatozoa, 579; of Antedon rosacea, 581, 582, 587; of fossil Crinoidea, 595; of Thecoidea, 596; of Carpoidea, 596; of young Ophiuroid, 613 Ambulacral ossicle, of Asteroidea, 432; of Asterias rubens, 434; of Ophiothrix fragilis, 481; compared to auricula of Echinus esculentus, 526; to inner plates of Palaeodiscus, 557; to side-plates of Crinoidea, 589 Ambulacral plate, of Echinus esculentus, 511; of Cidaridae, 533; of Sphaerechinus, 539; of Strongylocentrotus, 539; of Echinarachnius parma, 544 Amines, 15 Ammodiscus, 59 Amnion, 613 Amniotic cavity, 613 Amoeba, 4 f.; reactions of, 7 f.; devouring a plant cell, 9; excretion of, 14 f.; motion of, 17 f.; respiration of, 17 f.; taxies of, 22 Amoeba, 51; habitat of, 57; posterior disc or sucker, 53; A. binucleata, 30, 52; A. coli, habitat, 57; A. limax, 5; form of amoebulae of Acrasieae, 90; motions of, 47 n., 52; A. polypodia in fission, 10; A. proteus, 5; brood-divisions of, 56 n. Amoeboid, motion, 5; stages of Acystosporidae, 97, 103 f.; zoospores of Trichosphaerium, 54, 56; gametes of Flagellata, 116 n. Amoebophrya, 86, 159, 161 Amoebula, 31, 51; of Myxomycetes, 91, 92; of Didymium, 92; of fever parasites, 104 Amphiaster (an aster in which the actines form a whorl at each extremity of the axis, which is straight), 222 Amphibia, hosts of Opalinidae, 111, 123 Amphiblastula, 226 Amphicaryoninae, 306 Amphidisc, 176, 177 f., 202 Amphidiscophora, 203 f. Amphihelia, 399 Amphileptus, 137 Amphimonadidae, 111 Amphimonas, 111 Amphinema, 273 Amphiprion percula, 378 Amphiura, 497; A. squamata (= elegans), 485 n., 497, 601 Amphiuridae, 497 Amphizonella, 51; test of, 53 Amphoriscidae, 192 Ampulla, of Millepora, 259, 260; of Stylasterina, 284, 285; of tube-foot of Asterias rubens, 441, 443; synonym of axial sinus of Ophiothrix fragilis, 487; of stone-canal of Echinus esculentus, 517; of tube-foot of Echinus esculentus, 517; of respiratory trees of Holothuria nigra, 563; of podia of Holothuria nigra, 566; of feelers of Aspidochirota, 568, 570; of Pelagothuria, 568, 570; of Molpadiida, 568; of Synaptida, 568; of Elasipoda, 571 Anabolic, 12 f. Anabolism, 12 f.; modes of, 15 f. Anal, cirrhi, 139 f.; papilla (tube) of Antedon rosacea, 581, 583; of Eucalyptocrinus, 596 Ananchytidae, 554, 559 Anapta, 577 Anatomy, of a starfish (Asterias rubens), 432 f.; of Ophiothrix fragilis, 479 f.; of Echinus esculentus, 504 f.; of Echinarachnius parma, 542 f.; of Echinocardium cordatum, 549 f.; of Holothuria nigra, 561 f.; of Antedon rosacea, 581 f. Anatriaene (a triaene of which the cladi or branches point backwards, in the same direction as the rhabdome or shaft), 224 Anchoring flagella, 114; of Dallingeria, 112; of Bodo saltans, 117 Ancistrum, 137 Anemonia, 381; A. sulcata, 381 Animal-feeding Protista, 38 Animals, defined, 39 f.; and plants, discussion on, 35 f.; Higher, 31, 38 Anisochela (a chela of which the two ends are unequally developed), 222, 234 Anisonema, 110 Anisospores of Radiolaria, 76, 85; of Collozoum inerme, 76 Anochanus, 554 Anopheles, intermediate host of malarial parasite, 103 f.; enemies of, 106; precautions against, 106 Antedon, 594; A. rosacea, 581, 582; external features, 581; skeleton, 582; alimentary canal, 583; water-vascular system, 583; nervous system, 583 f.; coelom, 585; genital organs, 586; muscles, 587; blood-system, 587; development of, 617 f.; A. eschrichtii, 594 Antennularia, 279; A. antennina, 279; A. ramosa, 279 Anterior, dorsal process, of ciliated band of Bipinnaria, 606; of Auricularia, 608; median process, of ciliated band of Bipinnaria, 606 Antero-lateral process, of ciliated band of Echinopluteus, 607 Anthea cereus, 381 Antheneidae, 471 Anthocaulus, 389 Anthocodia, 330 Anthocyathus, 388, 389 Anthomastus, 333, 349 Anthomedusae, 262 f. Anthophysa (Flagellata), 111, 112 f.; (Siphonophora, Physophorinae), 308, 302 Anthoptilidae, 362 Anthoptilum grandiflorum, 362 Anthozoa, 326 f.; commercial importance, 328 Antipatharia, 407 f. Antipathella, 408; A. gracilis, 408 Antipathes, 408; A. ternatensis, 409 Antipathidea, 367, 371, 407 f. Antiseptic properties of "aromatic" compounds, 36 n. Anuncinataria, 203 Anus, of Ciliates, 143 f.; of Stylonychia, 139 f.; of Carchesium, 147; of Vorticella, 156; of Asterias rubens, 434; of Echinus esculentus, 516; of Echinarachnius parma, 546; of Pygastrides relictus, 548; of Euclypeastroidea, 549; of Echinolampas, 554; of Neolampas, 554; of Holothuria nigra, 560; of Antedon rosacea, 582; of Dipleurula larva, 604; of Asterina gibbosa, 611 Aphodal, 210 Aphrothoraca, 70 Aplanospore, 31 Aplysilla, 196 Aplysina, 225 Apocyte, 30, 32 Apocytial, condition, 32; forms among Myxosporidiaceae, 107 f.; Rhizopoda, 52 Apolemia, 308 Apoleminae, 307 Apopyle, 170 Aporosa, 397 Appendicularia, host of Gymnodinium pulvisculus, 132 Aquatic organisms, minute, distribution of, 47 n. Arachnactis, 373, 411; A. albida, 411; A. americana, 411; A. lloydii, 411 Arachnoides, 549 Arbacia, 520, 538 Arbaciidae, 530, 531, 532, 538, 558 Arbacioid type of ambulacral plate, 531, 538 Arcadomyaria, 324 Arcella, 51, 53; A. vulgaris, 55 Archaeocidaridae, 557, 558 Archaeocyte, 171 Archaster, 467; A. bifrons, 467 Archasteridae, 456, 466 Archenteron, definition of, 604 Archer, on Protozoa, 45; on Heliozoa, 71 Archicoel, 450 Arcuothrix, 52; transition between pseudopodium and flagellum in, 47 n. Arenaceous Foraminifera, 58 f.; Carpenter on, 63 f.; labyrinthine structure in, 66 Argas persica, 121 Aristocystis, 599, 599 Aristotle, 166 Aristotle's lantern, of Echinus esculentus, 515, 516, 524, 525; variations of, in Endocyclica, 531; of Echinarachnius parma, 546, 547; absent in Echinocardium cordatum, 550 Arm, of Asteroidea, 431, 432, 453; of Ophiothrix fragilis, 479; of Ophiuroidea, 481, 491; of Crinoidea, 580, 589; of Antedon rosacea, 581; of Antedon (other species), 594; of Hyocrinus, 590; of Rhizocrinus, 591; of Bathycrinus, 591; of Pentacrinidae, 592; of Holopus, 594; of Eudiocrinus, 594; of Inadunata, 595; of Articulata, 595; of Camerata, 595; development of, in Asterina gibbosa, 611; in Antedon rosacea, 620 Arm-spines, of Ophiothrix fragilis, 479; of Ophiuroidea, 491; of Ophiothrix, 492; of Ophiacantha, 492; of Ophiopteron 492 Aromatic compounds in relation to nutrition and antisepsis, 36 Arthropods, hosts of Gregarines, 97 f. Articulata, 595 Ascitic dropsy, Leydenia associated with, 91 Ascon, 185 Asconema setubalense, 221 Asexual reproduction of Asteroidea, 459; of Linckia, 459; of Asterina wega, 459 Ashworth, 331 n. Asiphonacea, 347 Asphyxia, its effect on contractile vacuole, 143 Aspidochirota, 568, 569, 570 f., 577, 578 Aspidosoma, 476 Aspirotrichaceae, 137, 148, 151, 153, 154 Assimilation, assimilative anabolism, growth, 9, 13, 15 f. Association, in Gregarines, 95, 98 f.; in Lankesteria ascidiae, 95 f. Astasia, 110, 112 Aster (= centrosome of mitotically dividing cell and peripheral rays), 25, 27; (a polyaxonid spicule), 184 Asterias, 473, 475; A. rubens, 432; external features, 432; pedicellariae, 433; skeleton, 434; coelom, 437; alimentary canal, 438; food, 439; water-vascular system, 441; nervous system, 444; perihaemal spaces, 448; blood-system, 449; genital organs, 451; A. glacialis, 473; pedicellariae, 434; A. hispida, 474; A. muelleri, 473; A. murrayi, 473; A. ochracea, 474; A. polaris, 474; A. spirabilis, 601, 602; A. tenuispina, 453 Asteriidae, 453, 458, 473 Asterina, 454, 456, 459, 461, 463; A. gibbosa, number of arms, 453; eggs of, 463; development of, 609, 610 f., 617; A. wega, 459 Asterinidae, 455, 458, 463 Asternata, 554 Asteroid stage in the development of Ophiuroidea and Echinoidea, 613, 622 Asteroidea, 430, 431 f.; compared with Ophiuroidea, 477 f.; compared with Echinoidea, 503, 558; mesenchyme of larva of, 602; development of, 605, 608, 609, 610 f.; phylogeny of, 621 Asteropsis, 471 Asterosmilia, 401 Asthenosoma, 536; A. hystrix, 536, 537; A. urens, 536 Astraeidae, 387, 399 Astraeopora, 390 Astrangia, 400; A. solitaria, 374, 400 Astrocnida, _501 Astrogonium_, 472 Astroides, 404 Astronyx, 501 Astropecten, 455, 459, 467; fossil, 475; A. irregularis, 468; movements, 468; burrowing habits, 469 Astropectinidae, 454, 458, 459, 467, 470 Astrophyton, 491, 501 Astropyle, 81 Astrorhiza, 59 Astrorhizidaceae, 59 Astroschema, 501; vertebra, 481 Astroschemidae, 501 Astrosclera willeyana, 194, 194 Astroscleridae, 194 Astylus, 287 Atelecrinus, 588, 594 Athoria (usually placed in a subfamily Athoriinae of the Physonectidae, 307), 300 Atolla, 322; A. bairdi, 322; A. gigantea, 322; A. valdiviae, 322 Atollidae, 322 Atoll, 390 f. Atorella, 314, 322 Atrophy, of oral apparatus of Ciliata during conjugation, 151 Attached, Foraminifera, 64; Flagellata, 112 f.; Ciliata, 152; Suctoria, 160 f., 162 Attachment, temporary, of Stentor, 155; permanent, of Rhizocrinus, 591; of Bathycrinus, 591; of young Pentacrinidae, 592; of Thecoidea, 596; of Cystoidea, 597; — temporary, of larva of sterina gibbosa, 610; of Brachiolaria larva, 612; of larva of Antedon rosacea, 619 Aulactinium, 79; A. actinastrum, 82 Aulena, 220 Aulocystis grayi, 208 Aurelia, 310, 314, 324; A. aurita, 312 Aureliania heterocera, 383 Auricula, of Echinus esculentus, 526; of Cidaridae, 531; of Arbaciidae, 531; of Echinarachnius parma, 546; represented by radial pieces of calcareous ring of Holothuroidea, 566 Auricularia, 607; metamorphosis of, 614, 615 Auronectidae, 301, 308 Aurophore, 308 Autodermin, 523 Automatic processes, so-called, 12 Autotrophic, 37 Autozooids, 333 Axial filament, of Heliozoan pseudopodia, 49, 71, 72, 74; of Actinophrys sol, 71; of Actinosphaerium eichornii, 72; of Radiolaria Acantharia, 80 Axial sinus, of Asterias rubens, 448; of Ophiothrix fragilis, 487; of Echinus esculentus, 517, 528; of Echinocardium cordatum, 552; of Holothuroid larva, 564; of larva of Antedon rosacea, 583; development of, in Asterina gibbosa, 609 Axifera, 353 Axinella, 216, 222, 225; A. erecta, 216 Axinellidae, 217 Axon, 444 Axoniderma, 216 Axopora, 262 Azoosporeae, 89

Babesia (= Piroplasma), 120 Bacteria, food of Myxomycetes, 92 f.; nutrition of, 36 Bactronella, 193 Baker, H., on organisms of putrefaction, 43; on Protozoa, 45; on Noctiluca, 134 f. Balanoglossus, larva and affinities of, 616 Balantidium, 137; habitat of, 152 Balbiani, on Protozoa, 45; on regeneration, 35 n.; on "Pébrine" (Nosema bombycis), 107 Barbados, Miocene deposit of Radiolaria, 87 Barotaxy, 20 Barrier reef, 390 f. Bary, A. de, on methods of culture of lower organisms, 44; on nature of Myxomycetes, 91 Basal granules, of cilia, etc., 138 n., 141 —see also Blepharoplast Basal plates, of Antedon rosacea, 584; of Crinoidea, 588; of Hyocrinus, 588, 590; of Atelecrinus, 588, 594; of Rhizocrinidae, 588, 590; of Thaumatocrinus, 588, 594; of Pentacrinidae, 591; of Holopus, 592; of Cystoidea, 598; of Blastoidea, 599 Bastian, H. Charlton, on spontaneous generation, 44 n. Bateson, 174 Bath sponge, 221 Bather, on Sympterura, 502; on classification of Crinoidea, 589; on phylogeny of Echinodermata, 622 Bathyactis, 404 Bathyanthus, 411 Bathycrinus, 589, 591 Bathypathes, 408 Bebryce, 356 Bell, F. J., 406 n.; on classification of Ophiuroidea, 494; of Endocyclica, 533 on relationships of Holothuroidea, 430 n., 622 Bell-animalcules, 155 f.; feeding of, 145 —see also Carchesium, Epistylis, Peritrichaceae, Vorticella, Zoothamnium Beloidea, 77 Beneden, E. van, on Sporozoa, 94; on pelagic Anthozoa, 411 Bernard, F., 241 n. Bernard, H. M., 386 n., 397 Beroe, 413, 423; B. cucumis, 416, 417; B. ovata, 416, 423 Beroidae, 414, 423 Berthold, on protoplasmic movements, 16 n. Bezzenberger, list of species of Opalina, 124 n.; on parasitic Ciliata, 152 n. Bicoeca, 111 Bicoecidae, 111 Bidder, 168, 172 n., 186 n., 235 n. Biemma, 224 Bigelow, 304, 420 n. Bile, 13 Biloculina, 59, 67 Biloculine, 66 Binary sex (= syngamy with marked inequality between the pairing cells), 33 f.; in Centropyxis, 57; in Stylorhynchus, 99; in Pterocephalus, 99; in Coccidiaceae, 100 f.; in Sarcocystis tenella, 108 n.; in Volvocidae, 127 f.; in Eudorina, 129; in Peritrichaceae, 151 f. Biomyxa, 58 Bionomics of Protistic life, 43 Bipinnaria, 605 f., 608; metamorphoses of, 612 Bipocillus (a microsclere consisting of a curved shaft, terminated by a cup-shaped expansion at each end, characteristic of the genus Iophon), 222 Birds, hosts of Acystosporidae, 103 Birth-pore, of brood-cavity of Suctoria, 161 Bisexual differentiation—see Binary sex Bivium, of Echinarachnius parma, 543; of Holothuria nigra, 561 Black Corals (= Gerardia, 406, and Antipatharia, 407) Bladder, of Rotifers and Platyhelminthes, 14 n. Blanchard, on Sporozoa, 94 Blastocoel, 603 Blastoidea, 580, 599 f. Blastomere, 603 Blastostyles, 265 Blasts of Coccidiaceae, morphology of, 120; of Acystosporidae, 104 f. Blastula, definition of, 603 Blepharoplast, 19; of Heliozoa, 72; of Flagellata, 109, 115; of Trypanosoma, 121; of nuclear origin in Trypanosoma, 109 n.; of T. noctuae, 120 f.; of Ciliata, 141 Block-musculature, of spines of Echinus esculentus, 506 Blood, Acystosporidae and Haemosporidae parasitic in, 97, 102 f.; Protomastigaceae parasitic in, in fever, 119 f. Blood-corpuscle, entered by Haemosporidae and Acystosporidae, 102 f., 104 f.; by Treponema and Trypanosoma, 120 Blood-system, of Asterias rubens, 449 f.; of Echinus esculentus, 529; of Holothuria nigra, 567; of Antedon rosacea, 587 Bloody rain, 125 Blowflies, alleged spontaneous generation of, 42 Bodo, 111, 119; B. caudatus, 116 n.; B. saltans, 114, 116 n., 117 f. Bodonidae, 111; movements of, 114 n. Body-cavity—see Coelom Bohemura, 502 Bolina, 419; B. infundibulum, 416 Bolinidae, 419 Bolinopsis, 419 Bolocera tuediae, 381 Borchgrevink, 310 n. Borgert, on Dictyochidae, 87; on fission in Aulacantha, 85; on phaeodium in Radiolaria, 81 n. Botanists, contributors to knowledge of Flagellates, 119 Bothriocidaris, 557, 561 Botryoidea, 79 Bougainvillia, 263, 264, 266, 269; B. ramosa, 269 Bougainvilliidae, 269 Boulenger, 294 n. Bourne, G. C., 246, 337, 338 n., 347 Bourrelet, 553 Boveri, on functions of chromatin, 28 n. Bowerbank, 168, 169, 234 n. Brachial ossicle, of Antedon rosacea, 582; of fossil Crinoidea, 595 Brachiolaria, 612, 613 Brachionus, often found with Euglena viridis, 124 Brachiopoda, 428, 579 Brachyenemic, 405 Brachyeneminae, 405 Brady, classification of Foraminifera, 58 f. Brain-Coral, 401 Branched, endoplasm, of Noctiluca, Trachelius, and Loxodes, 133, 153; meganucleus, of Dendrosoma, 160; theca, of Dinobryon, 112; of Schizotricha, 152 Branching colony, of Carchesium, Epistylis, Zoothamnium, 158 Brandt, Karl, on commensals and parasites of Radiolaria, 87 n.; on Radiolaria, 88 Breeding temperature of Protozoa, 47 Breeze Flies, intermediate hosts of Trypanosoma evansii, 119 Briareidae, 350 Brisinga, 474 Brisingidae, 453, 454, 474 Brissidae, 556 Brissopsis, 556; B. lyrifera, 556 Brittle Star—see Ophiuroidea Brood-cavity, in Suctoria, 160 f., 162 Brood-cell, 31 Brood-cyst, of Proteomyxa, 88 f. Brood-division, brood-formation, 30 f.; in Rhizopoda, 56 f.; in Foraminifera, 67 f.; in Radiolaria, 85 f.; in Proteomyxa, 49, 88 f.; in Sporozoa, 48, 94 f.; in Flagellata, 109, 115, 117 f.; in Polytomeae, 115; in Chlamydomonadidae, 115; in Paramoeba eilhardii, 116 n.; in Choanoflagellates, 122; in Proterospongia, 122; in Volvocidae, 127 f.; in Ciliata, 147; in Colpoda cucullus, 147, 153; of male Peritrichaceae, 151 f., 157; retarded, 31 f. Brood-mother-cell, 31 Brood-pouch, of Pteraster, 465, 466; of Hemiaster philippi, 556, 602; of Anochanus, 554; of Cucumaria laevigata, 602; of Psolus ephippifer, 602 Brooks, 288, 290, 308 n. Brown colour of lakes or ponds often due to Dinoflagellates, 131 Browne, 273, 281 n., 291 n., 312 Bruce, Col. and Mrs., on Trypanosomic fever and sleeping sickness, 120 Bubbles of carbon dioxide formed in Arcella, etc., 53 Buccal sinus of Holothuria nigra, 566 Buccal tentacle—see Buccal tube-foot Buccal tube-foot (and tentacle), of Ophiothrix fragilis, 486; of Echinus esculentus, 518; of Echinocardium cordatum, 551, 561; of Holothuria nigra, 561; of Spatangoidea, 577; development of, in Holothuroid pupa, 615 Budding, in Trichosphaerium, 54; in Rhizopoda, 56; in Acanthocystis, 73; in Acantharia, 86 n.; in Spirochona, 147; in Suctoria, 160, 162; in Sponges, 177 f., 228, 229, 230; in Hydrozoa, 250 f., 263, 275; in Medusae, 270, 296; in Scyphistoma, 317; in Alcyonaria, 340; in Zoantharia, 371 Bud-fission in testaceous Rhizopoda, 55; in Euglypha, 29 Buffon, on organisms of putrefaction, 43 Bulimina, 59 Bulk and surface of organism, ratio between, 14 Bunodactis gemmacea, 378 Bunodeopsis, 382 Bunodes, 378, 382; B. gemmacea, 382 Bunodidae, 382 Burrowing habits, of certain Asteroidea, 461; of Astropecten, 469; of Paxillosa, 469; of Porcellanasteridae, 471; of Strongylocentrotus lividus, 541; of Echinarachnius parma, 546; of Echinocardium cordatum, 549; of Spatangus purpureus, 555; of Molpadiida, 575; of Synaptida, 576; of Synapta inhaerens, 577 Burrowing Urchins, 529 Bursaria, 137, 155 Bury, on primary axial sinus of Holothuroid larva, 564; on change in position of mouth during metamorphosis of Auricularia, 614 Bütschli, on protoplasm, 16 n.; on paramylum, 95 n.; on Protozoa, 46; on Cystoflagellates, 135; on classification of Ciliata, 137; on Strombidium and Torquatella, 155 n.; on Sponges, 168, 172 n.

Caecum (diverticulum), of alimentary canal of Echinocardium cordatum, 551; of alimentary canal of Elasipoda, 569, 571 Caenomorpha, 137, 141 n., 154; C. uniserialis, 155 Cake-urchins = Clypeastroidea, q.v. Calcaire Grossier, 70 Calcarea, 184 f. Calcareous ooze, 114 Calcareous ring, of Holothuria nigra, 566; of H. cinerascens, 567; of Phyllophorus rugosus, 567 Calcaromma calcarea, 83 Calcituba, 59; growth of, 64; pylomes of, 64 Calices of Madreporaria, 371 Calicoblasts, 385 Calkins, on nucleus in Protozoa, 25 n.; on Protozoa, 46; on rhythm in life-cycle of Ciliata, 148 n. Calliactis (family Sagartiidae, 381); C. parasitica, 378 Callianira, 418 Callianiridae, 417 Calthrop, 184; of Radiolaria, 83 Calycophorae, 300 f. 305 Calymma, 79, 82 Calymma, 420 Calymmidae, 420 Calyptoblastea, 275 f. Calyx, of Echinus esculentus, 513; of Echinarachnius parma, 545; of Pelmatozoa, 579; of Crinoidea, 580, 588 f.; of Carpoidea, 580; of Cystoidea, 580, 598; of Blastoidea, 580, 599; of Holopus, 592; of fossil Crinoidea, 595 Camerata, 595 Campanularia, 280 Campanulariidae, 280 Campascus, 52; test of, 55 Camptolithus, 346 Camptonema, 70, 73 Canalaria, 201 Canals, "feeding," afferent, or replenishing of contractile vacuole system in Ciliata, 14, 143, 146; of Stylonychia, 139 f.; of Stentor, 156 Cannopora, 283 Cannopylaea (= Phaeodaria), 76 Cannotidae, 278 Capillitium of Myxomycetes, 90 f., 92 Capnea sanguinea, 383 Capria, _321 Caravella_, 308 Carbohydrates, formation of, 33 Carbon dioxide, attracts Paramecium, 23; excretion of, 8, 13 f.; secreted by Arcella, etc., 53 Carchesium, 138; feeding of, 145, 158 Carinal ossicle of Asteroidea, 436 Carlgren, 378 n. Carmarina, 295 Carpenter, P. H., on the classification of the Crinoidea, 589 Carpenter, W. B., classification of Foraminifera, 58; on their true nature, 62; on their structure, 63 f.; on Arenacea, 65 f.; on the nervous system of Antedon rosacea, 585 Carpoidea, 580, 596 f. Carter, on Protozoa, 45; on Sponges, 167, 180, 208, 237 n.; on fossil Hydrozoa, 270 n. Caryophyllia, 386, 398 Cash, on Rhizopoda, 58 n. Cassidulidae, 554 Cassidulina, 59 Cassiopea, 324 Cassiopeidae, 324 Castellani, on Trypanosomic fever and sleeping sickness, 120 Catabolic, catabolism, 13 f., 24 Cataclysmal metamorphosis of Dipleurula, 613 Catallacta, 89 Catostylidae, 325 Cattle, Trypanosomic diseases of, 119 f. Caudal cirrhi, 139 f. Caudina, 575 Caullery and Mesnil, on Actinomyxidiaceae, 98 n. Cavernularia, 359, 364; C. obesa, 364 Cell, 3 f.; definition of, 3; nutrition of, 15 f., 35 f.; -membrane of ovum of Sea-urchin, 7; -wall, 3; in Flagellates, 109, 113; in Dinoflagellates, 130; -boundary in Flagellates, 113; -division, 24 f., 25, 27; Spencerian division, 31 f.; -unions in Volvox, 126, 127; collar-, of Choanoflagellates, 121, 122; of Sponges (= choanocytes), 171, 176, 186 Cellular relationship explained, 10 Cellulose, 37; cell-wall of holophytic Flagellates, 113; in Dinoflagellates, 130 Central blood plexus—see Heart Central capsule, 49, 76, 77, 82, 84; its functions in regeneration, 35; of Collozoum inerme, 76 Centrifugal force, stimulus of, 19 f. Centriole, 25, 27 Centripetal canals, 289 Centro-dorsal ossicle, of Crinoidea, 580; of Antedon rosacea, 582; of Actinometra, 588, 594; of Atelecrinus, 594 Centrogenous (used of spicules = meeting in a common centre and growing outwards), 76 Centropyxis, 51; test of, 55; C. aculeata, reproduction of, 57 Centrosome, 19, 26 f.; of Heliozoa, 72; (= blepharoplast) in Flagellates, 115 Centrosphere, 25 f., 27 Centrostephanus, 522, 539; C. longispinosus, 522, 532, 539 Cephalis (= uppermost chamber of monaxonic Radiolarian shells), 83 Cephalodiscus, 617 Cephalont of Gregarines, 98 Cephalopoda, erroneous reference of Foraminifera to, 62 Cephea, 325 Cepheidae, 324 Ceratella, 263, 271; C. fusca, 271 Ceratellidae, 271 Ceratium, 110; habitat of, 131 Ceratosa, 211, 220 Cercomonas, 116 n., 119; C. dujardini, gametes of, 116 n. Cereactis (family Actiniidae, 381); C. aurantiaca, 378 Cerianthidea, 367, 373, 377, 409 Cerianthus, 328, 366, 409; nematocyst of, 247; C. americanus, 411; C. bathymetricus, 411; C. lloydii, 411; C. membranaceus, 370, 410, 411; C. oligopodus, 411; C. vogti, 411 Cestidae, 420 Cestoidea, 413, 414, 416, 420 Cestus, 420; C. pectenalis, 420; C. veneris, 417, 420 Chaetetidae, 346 Chalarothoraca, 71 Chalina, 217, 223 Chalk, Foraminifera, etc., in, 69 f. Challengeridae (a family of Phaeogromia, 79); shells, skeleton of, 84, 85 Chambered organ, of Antedon rosacea, 584; of Pentacrinidae, 592 Chambers, of Foraminiferal shell, 62 Chapman, on Foraminifera, 58 n., 70 Charistephane, 417 Charybdea, 311, 314, 319; C. xaymacana, 310, 319; C. marsupialis, 319; C. grandis, 319 Charybdeidae, 318 Cheilostomella, 59 Cheilostomellaceae, 59 Chela (a complex microsclere derived from a sigma and consisting of a curved shaft bearing recurved processes), 234 Chemical, reactions, of protoplasm and of vacuoles, 13; substances in solution, 19, 22 f.; rays of spectrum in relation to plant pigments, 36 n. Chemiotaxy, 23; its rôle in syngamy, 34; of Coccidians, 100 Chirodropidae, _319 Chirodropus_, 319 Chironephthya, 349; C. variabilis, 338 Chiropsalmus, 319 Chitin, 37 Chlamydomonadidae, 111, 125, 126; brood-division of active, 115 Chlamydomonas, 111, 125 f.; barotaxy of, 20; conjugation of, 115 f.; Dill on, 119 n. Chlamydophora, 71 Chlamydophrys, 52; C. stercorea, reproduction of, 57; habitat of, 57 f. Chloramoeba, 110 Chloromonadaceae, 110; trichocysts in, 113 n. Chlorophyll, 36 n.; in Flagellates, 115 n.; bodies of Euglenaceae, 124 f. Chloroplasts (= chlorophyll bodies), of Eutreptia viridis, 124 f. Choanocytes, 171, 176, 186, 200, 237 —see also Collar-cells Choanoflagellata, Choanoflagellates (= Craspedomonadidae, 111), 121, 122 f.; in relation to Sponges, 41, 171, 181 Choanophrya, 159 f., 162; C. infundibulifera, 162 Choanosome, 170 Chondrilla, spicules of, 233 Chondrioderma, 90; C. diffusum, 93 Chondrocladia, 216 Chondrophoridae, 301, 308 Chone, 213, 214 Choristida, 212 Chromatin, 6 f.; function of, in cell-division, 24 f.; of ovum of Sea-urchin, 7; of Radiolaria, 81; -granules, 7, 24 Chromatophore, 13, 21, 36 f., 113, 115; of Sphaerella, 126 —see also Chromoplastid, Chlorophyll, Plastid Chromidia, 30; of Rhizopoda, 51; of Foraminifera, 67 f. Chromoplastid, 21, 36 f.; of Zooxanthella, 86 —see also Chromatophore Chromosomes, 25 f., 27; functions of, 28 f. Chromulina, 110 Chrysamoeba, 110 Chrysaora, 312, 315, 316, 323; C. isosceles, 311, 314, 323 Chrysogorgia, 355 Chrysogorgiidae, 355 (= Dasygorgiidae, 333) Chrysomitra, 302, 309 Chrysomonadaceae, 110; external plasmic layer of, 113; symbiotic, 86, 125 Chun, 197 n., 300, 307 n., 308, 414 n. Chunella, 360, 363 Chytridieae, movements and affinities of, 114 n.; relations of, 40, 48, 119 Cidaridae, 530, 531, 532, 533, 558 Cidaris, 533, 534; C. (Dorocidaris) papillata, 534 Cienkowsky, on Monadineae (= Flagellates and Proteomyxa), 40, 89; on Radiolaria, 88; on Zooxanthella, 86; on Cystoflagellates, 135 Cilia, 17, 18; of Protozoa, 47; paroral, 156 n.; preoral, 139; of Trichonymphidae, 123; of Opalina, 123; of Maupasia, 124; of Ciliata, 141; organs formed of combined, 138, 141, 413; sensory, of Stylonychia, 138; Schuberg, A., on, 141 n. Ciliary motion, 18; mechanism of, 18 n. Ciliata, 18, 41, 137 f., 181; animal nutrition, 40; conjugation, 149 f.; contractile vacuole, 14 f., 143; encystment, 147 f.; feeding, 145; fission, 147 f.; form of body, 141; galvanotaxy, 22; infested by Suctorian parasites, 160 f.; gut, 146; mouth, 145; nuclear apparatus, 144 f.; parasitic, 152; pharynx, 145; pellicle, 141; regeneration, 35, 145; relations to Metazoa, 41; rheotaxy, 21; Suctoria allied to, 159; thigmotaxy of, 20; tubicolous, 152; Zooxanthella symbiotic with, 125 Ciliated, buds of Suctoria, 159, 160 f., 162; epaulette, 607 Cilioflagellata (= Dinoflagellata, given by misinterpretation of transverse flagellum), 130. Ciliophrys, 75 n., 89 Cilium of Noctiluca, 133 Cinachyra, 212, 215; C. barbata, 212 Cinclides, 369 Cinetochilum, 137 Ciocalypta, 225 Cirripathes, 408; C. spiralis, 408 Cirrus, of Crinoidea, 430, 580; of Antedon rosacea, 581, 585; of Rhizocrinidae, 588, 590; of Pentacrinidae, 588, 591, 592; of Rhizocrinus, 591; of Comatulidae, 594; of Actinometra, 594; of Antedon, 594; development of, in A. rosacea, 620; of fossil Crinoidea, 595 Cladocarpus, 279 Cladocora, 373, 400 Cladocoryne, 272 Cladocrinoidea, 595 Cladonema, 266, 270; C. radiatum, 267 Cladonemidae, 270 Cladopathes, 408 Cladophiurae, 491, 494, 502 Cladorhiza, 216 Cladotyle (a rhabdus on which one actine is branched, the other tylote or knobbed at the extremity), 222 Claparède and Lachmann on Protozoa, 45; on Suctoria, 162 Clark—see James-Clark Classification, of Protozoa, 48 f., 50; of Rhizopoda, 51 f.; of Foraminifera, 58 f.; of Heliozoa, 70 f.; of Radiolaria, 76 f.; of Proteomyxa, 90; of Sporozoa, 97; of Flagellata, 109 f.; of Protomastigaceae, 111; of Volvocaceae, 111; of Infusoria, 136; of Ciliata, 137; of Suctoria, 159; of Sponges, 183 f.; of Coelenterata, 249 f.; of Ctenophora, 417 f.; of Eleutherozoa, 430 f.; of Asteroidea, 459 f.; of Ophiuroidea, 491 f.; of Echinoidea, 529 f.; of Endocyclica, 532; of Clypeastroidea, 548 f.; of Spatangoidea, 552; of Holothuroidea, 567 f.; of Pelmatozoa, 580; of Crinoidea, 589 f. Clathria, 225 Clathrina, 186, 221, 231; C. blanca, larva of, 227 Clathrinidae, 185 f. Clathrissa, 223 Clathrozoon, 277, 279; C. wilsoni, 279 Clathrulina, 71, 73, 74 Clava, 272; C. squamata, 263 Clavatella, 267, 270 Clavatellidae, 270 Clavidae, 272 Clavularia, 330, 334, 344; C. viridis, 329, 337, 343 f., 344 Clavulariidae, 344 Clearing of tissues, physical explanation of, 11 Climacograptus, 282 Cliona, 219, 224 Clionidae, 218 Cloaca of Holothuria nigra, 563 Clypeaster, 548, 549 Clypeastridae (= Echinanthidae), 549 Clypeastroidea, 529, 542 f., 556, 559, 566 Clytia, 280; C. johnstoni, 275, 280 f. Cnidoblast, 247, 248 Cnidocil, 248 Cnidopod, 248 Cnidosac, 300 Coalescence of individual Rhizopods during bud-fission, 55 Coccidiaceae, 97, 99 f.; relations to Trypanosoma, 120 Coccidiidae, 97, 99 f., 101 Coccidiosis, 102 Coccidium, 99 f., 101 f.; C. cuniculi, 102; C. lacazei, syngamy of, 101; C. schubergi, 99 f., 101 Coccolithophora, 110 Coccolithophoridae, in Chalk, 70; wall of, 114 Coccoliths, 83, 110, 114, 242 Coccoseridae, 346 Coccospheres, 83, 114 Cockroach, Lophomonas parasitic in gut of, 123 Codaster, 599 Codosiga, 111 Coelenterata, 243 f.; definition, 245; almost all immune from Gregarines, 99 Coeliac canal of Antedon rosacea, 586 Coelogorgia, 349 Coelogorgiidae, 349 Coelom (including body-cavity), 428; of Asterias rubens, 437; of arm of Ophiothrix fragilis, 480; of Echinus esculentus, 516; of Holothuria nigra, 562; of Antedon rosacea, 585; development of first rudiment in larva, 605; subsequent development in Dipleurula, 608, 609; in Asterina gibbosa, 611; in Antedon rosacea, 618, 619 Coelomic nervous system, of Asterias rubens, 448; of Ophiothrix fragilis, 488; of Echinus esculentus, 524; of Holothuria nigra, 566; of Antedon rosacea, 584, 585 Coeloplana, 412, 422; C. mitsukurii, 422 Coeloplanidae, 422 Coenocyte, 30 Coenograptus, 282 Coenopsammia, 404 Coenosteum, 371, 387 Coenothecalia, 344 Cohn, Ferdinand, on cultures of Schizomycetes, etc., 44 Cold-blooded Vertebrates, as hosts of Haemosporidae, 102 Coleps, 137; mail-like pellicle of, 141, 152; C. hirtus, group feeding, 150 Collar, of Choanoflagellates, 121 f., 122; of peristome of Vorticella, etc., 156 Collar-cells, in Choanoflagellates, 121 f., 122, 171, 237; of Calcarea, 186; of Non-Calcarea, 176, 200 —see also Choanocytes Collencyte, 171 Colletocystophores, 320 Collida, 77 n. Colloblasts, 414 Collodaria, 77 Colloidea, 77 Collosphaera, 77; symbiotic Diatoms in, 86 Collosphaeridae, 85 Collozoidae, 85 Collozoum, 77; C. inerme, 76 Collyritidae, 559 Colobocentrotus, 532, 542 Colonial, cells, 31; Protista, 31 Colony, 31; of Collozoum inerme, 76; -formation in Polycyttarian Radiolaria, 84 f.; in Flagellata, 113; of Choanoflagellates, 121, 122; in Vorticellidae, 158; of Volvocidae, 126 f.; of Pandorina, 128 f.; of Eudorina, 129 Colour, red, of lakes and ponds, often due to Dinoflagellata, 131 Coloured vegetal nutrition, 36 f. Colouring matter of chromatophores of Flagellates, 115 n. Colpidium, 137; C. colpoda, diagram of conjugation, 149; nuclear relations in conjugation, 151 Colpoda, 137; C. cucullus, 153; brood-fission in cyst, 147 Columella, 370, 385 Columnals, 619 (= Stem-ossicles, q.v.) Columnaria, 344 Comatula = Antedon, q.v. Comatulidae, 594 Combs of Ctenophora, 141, 412 Comitalia, 201 Commensals, of Heliozoa, 73; of Radiolaria, 80, 86 f.; of Infusoria, 153 f.; —see also Zoochlorella, Zooxanthella, and Symbiosis Comminator muscles of Aristotle's lantern, 526 Commissure of radial cords of aboral nervous system of Antedon rosacea, 585 Compasses (or radii) of Aristotle's lantern, 526 Conant, 319 Conaria larva, 302 Conchophtheirus, 137 Conchula, 380 Confervaceae, related to green Flagellates, 48 Confervoid form of Hydrurus, 113 Conjugatae, syngamy of, compared to certain Chlamydomonads, 126 Conjugation, 33 f.; of Rhizopoda, 54, 56 f.; of Trichosphaerium, 54, 56 f.; exogamous, in Foraminifera, 68 f.; of Heliozoa, 72, 73 f.; of Sporozoa, 95 f.; of Lankesteria, 95 f.; of Monocystis, 96; of Gregarines, 97, 100; of Stylorhynchus, 99; bisexual, of Sarcocystis tenella, 108 n.; of Flagellates, 115; of Bodo saltans, 117; of Trypanosoma, 120; by a fertilising tube in Chlamydomonas, 125; of Volvocaceae, 127 f.; of Volvox, 127 f.; isogamous and endogamous, of Stephanosphaera, 128; in Dinoflagellates, 131 n.; of Noctiluca, 133; of Ciliata, 148 f.; of Paramecium caudatum, 148; of Colpidium colpoda, diagram, 149; of Peritrichaceae, 151 f., 157; of Vorticella, 157; of Suctoria, 161; of meganucleus in Dendrocometes, 161, 162 —see also Syngamy, Fertilisation Conoclypeus, 558 Constancy of type in Protista, 42 f. Conte, 292 n. Contractile vacuole, 5, 10, 14 f.; of Amoeba polypodia, 5, 10; of fresh-water and brackish Protozoa, accessory spaces and canals, 47; of Rhizopods, 52; of fresh-water Allogromidiaceae, 60; of Microgromia socialis, 60; of Heliozoa, 71, 72, 74; of zoospore of Clathrulina, 74; of Myxomycetes, 92; of Flagellata, 110, 112, 115; of Cryptomonas, 112; of Diplomita, 112; of Oikomonas, 112; of Tetramitus, 112; of Trachelomonas, 112; of Bodo saltans, 117; of Choanoflagellates, 122; absent from Opalinidae, 123; of Euglenaceae, 125; of Volvox, 126; of Ciliata, 143 f.; in fission, 147; of Stylonychia, 139 f. of Stentor, 156; of Vorticella, 157; of Suctoria, 160 f., 162 Contractility, 8, 9; muscular mechanism of, 14 f. Contraction, of Amoeboid cell, 16 f. Copepoda, infested by Epistylis, 158 —see also Cyclops Coppinia, 280; C. arcta, 280 Coprolites, Radiolaria in, 87 Copromyxa, 90 Coral, 326, 365; Organ-pipe, 343; Precious (= Red), 326, 352; Flexible (= various Alcyonaria), 326; Stony (= Madreporaria), 326, 384 f.; Brain-, 401; Black (= Gerardia, 406, and Antipatharia, 407); -Reefs, 390 f.; Reef-, 389 f. Coralliidae, 335, 352; commercial importance, 328 Corallimorphidae, 383 Corallimorphus, 383 Corallium, 333, 350, 352; C. boshuensis 352; C. confusum, 352; C. elatius, 352; C. inutile, 352; C. japonicum, 352; C. johnsoni, 352; C. konojoi, 352; C. nobile, 340 n., 341, 352; C. pusillum, 352; C. reginae, 352; C. stylasteroides 352; C. sulcatum, 352 Corbula, 276 Cordylophora, 269, 272 Cormidia, 301, 305 Cornularia, 334, 344 Cornulariidae, 344 Cornuspira, 59; shell of, 64 Corona, of Echinus esculentus, 504, 511; of Endocyclica, 530; of Cidaridae, 530; of Echinothuriidae, 530, 535; of Temnopleurinae, 539 Coronaster, 474 Coronata, 314, 321 Cortex, 190, 191, 213; gastral cortex, 188 Corticata, 49 n. Corydendrium (family Tiaridae, 273); C. parasiticum, 269 Corymorpha, 263, 265, 266, 273; C. nutans, 273 Corymorphidae, 273 Corynactis, 372, 383; C. viridis, 383 Coryne, 272 Corynidae, 272 Cosmiolithus, 346 Costae, 385, 387; of Ctenophora, 413, 416 n. Costia, 111; C. necatrix, produces epidemics in fresh-water fish, 119 Cothurnia, 138, 158 Cotte, 218 n. Cotton-spinner, 564 Cotylorhiza, 325 Coupled cell, 31, 33 f.; in Flagellates, 116 f. —see also Zygote Covering-plates, of arms of Ophiuroidea, 491; of arms of Crinoidea, 589; of Hyocrinus, 589, 590; of Rhizocrinidae, 589, 591; of Pentacrinidae, 589; of Antedon, 589, 594; of Thecoidea, 596; of Blastoidea, 599 Crambessa, 325 Crambione, 325 Craniella, 213, 213, 214; C. cranium, 222 Craspedomonadidae, 111, 115 n., 121 f., 122; transverse division in, 115 n. —see also Choanoflagellata Crescent (gametocyte of Laverania), 104 f. Cretaceous firestone of Delitzet contains Peridinium, 132 Cribrella, 457, 462; C. (Henricia) sanguinolenta, 462, 463; C. laeviuscula, 462 Cribriform organs, 470 Cricket, Mole-, Lophomonas parasitic in gut of, 123 Crinoidea, 430, 580 f.; development of, 617 f. Crinorhiza, 212, 216 Cristellaria, 59 Crotalocrinus, 595; C. pulcher, 595 Crustacea, small, rheotaxy of, 21 Cryptabacia, 404 Cryptogams, Higher, spermatozoa of, 38 Cryptoglena, shell of, 113 Cryptohelia, 284, 287; C. ramosa, 285 Cryptomonadaceae, 110 Cryptomonas, 110 Cryptozonate, 454 Crystals, in isospores of Collozoum inerme, 76; proteid, 37 Ctenocella, 357 Ctenodiscus, 458, 471 Ctenophora, 412 f.; comb-plates of, 141 Ctenophoral plates, 141, 412 Ctenoplana, 416, 421 Ctenoplanidae, 421 Cubomedusae, 310, 316, 318 f. Cucumaria, 573; C. crocea, 573, 602; C. laevigata, 602 Cuénot, on Sporozoa, 94; on reproduction of Monocystis, 96 n. Culcita, 453, 472; C. tetragona, 453 Culex, host of Haemoproteus or Proteosoma, 103; intermediate host of a Trypanosoma, 120 Cultures, pure, 43 Cunanthidae, 296 Cunarcha, 296 Cunina, 296; C. proboscidea, 296; C. rhododactyla, 296 Cunoctantha, 296; C. octonaria, 295 Cup (= theca), of Flagellates, 113; of Salpingoeca, 122; of Acineta, 159, 160 —see also Theca, Tube Cupulita, 307; C. sarsii, 304 Current, 169, 171, 234 f.; electric, stimulus of, 19, 22; in liquid, relation of protoplasmic movements to, 7, 19, 21 Cuticle, of Dinoflagellata, 130; of Gregarines, 96; of Noctiluca, 133 —see also Membrane, Pellicle Cuticular shell of Flagellates, 113 Cuvier, 245, 246 Cuvierian organs of Holothuria nigra, 564 Cyanaea, 311, 312, 324; C. capillata, 311, 324; C. lamarcki, 324 Cyanaeidae, 324 Cyathaxoniidae, 394 Cyatholiths, 114 Cyathophyllidae, 394 Cyathophyllum, 394 Cycads, spermatozoa of, 38 Cyclidium, 137 Cyclocnemaria, 397 Cyclomyaria, 325 Cyclops, host of Choanophrya, 159; of Rhyncheta and other Suctoria, 159 f., 162; of Vorticellidæ, 158 Cycloseridae, 404 Cydippidea, 417 Cydippiform stage of Lobata and Cestoidea, 414 Cydonium milleri, 222 Cymbonectes, 306 Cymbonectinae, 306 Cyphoderia, 52 Cyrtoidea, 79 Cyst (a closed membrane distinct from the cytoplasm around a resting-cell or apocyte), 37, 39; cellulose-, 37; chitinous, 37; growth of vegetal cell in, 37; of Protozoa present in dust, 47; of Centropyxis aculeata, 57; of Chlamydophrys stercorea, 57; of Amoeba coli, 57; of Actinophrys sol, 72; of Actinosphaerium, 73 f.; of Flagellata, 109, 117 f.; brood-, of Paramoeba eilhardii, 116 n.; of Bodo saltans, 117; of Opalina, 123 f.; of Volvocaceae, 128; of Dinoflagellates, 131; of Pyrocystis, 131, 132; of Ciliata, 147; of Colpoda cucullus, 147, 153; temporary (hypnocyst) of Rhizopoda, 57; of Proteomyxa, 88; of Myxomycetes, 91; -wall, of Acystosporidae, 104 f. Cystiactis, 382 Cystid—see Cystoidea Cystiphyllidae, 394 Cystoflagellata, 110, 132 f. Cystoidea, 580, 597 f. Cytogamy, 33 f. Cytoplasm, 6; of ovum of Sea-urchin, 7; granular, nutritive, of muscle cell, 19; in cell-division by mitosis, 26 f.; during syngamy, 34

Dactylometra, 311, 323; D. lactea, 312 Dactylopores, 257 Dactylozooids, 264; of Hydractinia, 264; of Millepora, 259; of Siphonophora, 299 Dale, on chemiotaxy, 22 Dallinger, W. H., and Drysdale, C., on Protozoa, 44, 45; on organisms of putrefaction, 44, 116 f.; on life-histories of Flagellates, 116 f. Dallingeria, 111, 112, 119; anchoring flagella of, 114; D. drysdali, gametes of, 116 n. Dalyell, 317 n., 375 Dangeard, on brood-division in active Chlamydomonadidae, 115; on Flagellata, 119 n. Dantec, Le, on protoplasmic movements, 16 n.; on peptic digestion in Protozoa, 16 Darwin, 328 n., 360, 391 Darwinella, 221 Dasygorgiidae, 333 (= Chrysogorgiidae, 355) Davenport on protoplasmic movements, 16 n., 19 n. Dawydoff, 423 Dead men's fingers (= Alcyonium digitatum, 349) Death, 11; by diffluence, granular disintegration or solution, 14 f.; by desolution, 15; necessary, of colonial cells of Volvox, 128; in Volvox and in Metazoa, compared, 130 Deep-sea deposits (Foraminifera), 70 Degen, on functions of contractile vacuole, 15 n. Degeneration, senile, among Ciliata, 148 Deglutition in Podophrya trold, 159 —see also Ingestion of food Deiopea, 419 Deiopeidae, 419 Delage, on protoplasm, 3 n.; on syngamy, 34 n.; on motion of flagella, 114 n.; on Sponges, 168, 174, 226; and Hérouard, on Protozoa, 46 Delap, M. J., 311 n. Deltoid plate of Blastoidea, 599 Demospongiae, 195, 209 f. Dendoryx, 224 Dendrite, 444 Dendrobrachia, 409 Dendrobrachiidae, 409 Dendroceratina, 209, 220, 221 Dendrochirota, 568, 569, 572, 577, 578 Dendrocometes, 159, 160, 161 f. Dendrograptidae, 281 Dendrograptus, 281 Dendrophyllia, 404 Dendy, 188 n., 192, 274, 275 Depastrella, 321 Depastridae, 320, 321 Depastrum cyathiforme, 321 Depressor muscles of compasses of Echinus esculentus, 527 Dercitus bucklandi, 221 Dermal, gill—see Papula; membrane, 170 Dermalia, 201 Dermasterias, 471 Desma (the megasclere which forms the characteristic skeletal network of the Lithistida, an irregular branched spicule), 215, 224 Desmacella, 224 Desmacidon, 222 Desmophyes, 307 Desmophyinae, 307 Desmothoraca, 71 Desolution of protoplasm, 11 f. Deutomerite, 98 Development, of Sponges, 226; of Scyphozoa, 316; of Alcyonaria, 341; of Zoantharia, 373; of Echinodermata, 601 f. Dextrin, 15 Diadematidae, 531, 532, 538 f., 558 Diadematoid type of ambulacral plate, 531, 539 Dialytinae, 192 Diancistra (a spicule resembling a stout sigma, but the inner margin of both hook and shaft thins out to a knife edge and is notched), 222 Diaphorodon, 59; shell of, 60 Diaseris, 404; asexual reproduction, 388 Diatomaceae, skeleton of, 84; symbiotic with Collosphaera, 86 Diatomin, 86; (?) in coloured Flagellates, 115 n. Dichoporita, 598, 599 Dicoryne, 268, 270 Dictyoceratina, 220 Dictyocha, 110 Dictyochida (= Silicoflagellata, 110), 79; in Phaeocystina, 86 f. Dictyocystis, 137; test of, 152 Dictyonalia, 201 Dictyonema, 281 Dictyonina, 202 Dictyostelium, 90 Dicyclica, 594 Dicymba, 308 Dicystidae, 97 Didinium, 137; trichocysts of, 143 Didymium, 90; D. difforme, 92 Didymograptus, 282 Diffluence, 14 f. Difflugia, 52; D. pyriformis, 55; test of, 55 Digestion, 9, 15 f.; of reserves in brood-formation, 33; in Carchesium, 147; in Starfish, 440 Digestive system—see Alimentary Canal Dileptus, 137, 152 n. Dill, on Chlamydomonas, etc., 119 n. Dimorpha, 70, 73, 75 n., 112 Dimorphism of chambered Foraminifera, 67 f. Dinamoeba, 51; test of, 53 Dinenympha, 111, 115; undulating membranes of, 123 Dinobryon, 110, 112 Dinoflagellata, 110, 113, 130, 131, 132; plastids of, 40; nutrition of, 113 Dinoflagellate condition of young Noctiluca, 134 Diphyes, 303, 307 Diphyidae, 306 Diphyopsinae, 307 Diplacanthid, 457 Dipleurula, definition, 605; forms of, 605-608 Diplocyathus, 277 Diplodal, 210 Diplodemia, 223 Diploëpora, 346 Diplograptus, 281, 282 Diplomita, 111 Diplopore, 597, 599 Diploporita, 598, 599 Diprionidae, 282 Directives, 367 Disc, of Vorticellidae, 155, 158; of Ophiothrix fragilis, 484 Discalia, 309 Discohexaster, 200 Discoidea, 77 Discoidea, 558 Discomedusae (= Ephyropsidae, 322 + Atollidae, 322 + Discophora, 323) Discomorpha, 137 Discooctaster, 200 Discophora, 310, 316, 323 f. Discorbina, 59, 63; reproduction of, 69 Discosomatidae, 383 Diseases, produced by Coccidiidae, 102; by Acystosporidae, 103 f.; by Flagellates, 119 f.; by Trypanosomes, 119 f.; Protozoic organisms of, 43 f. Dissepiments, 385, 387 Dissogony, 419 Distichopora, 284, 286 Distomatidae, 110 Distribution of Protozoa, 47; of Sponges, in space, 239 f.; in time, 241 Disyringa dissimilis, 209, 214, 215 Diverticulum—see Caecum Division, binary, 10; reduction-, 75 n. Dixon and Hartog on pepsin in Pelomyxa, 16 Dobie, 167 Doederlein, 193 n. Doflein, 46; on parasitic and morbitic Protozoa, 94 n.; on syngamy of Cystoflagellates, 135 Dohrn, on carnivorous habits of Sphaerechinus, 516 Dolichosporidia (= Sarcosporidiaceae), 98, 108 Doramasia, 306; D. picta, 303 Dorataspis, 78; skeleton, 80 Dorocidaris—see Cidaris Dorsal elastic ligament of Antedon rosacea, 587 Dorso-central plate of Echinarachnius parma, 543 Dourine, disease of horses and dogs, 119 Drepanidium (= Lankesterella), 97, 102 Dreyer, on genera and species of Radiolaria, 87 f.; on skeleton of Radiolaria, 82 n. Dropsy, ascitic, associated with Leydenia, 91 Drysdale and Dallinger, on organisms of putrefaction, 44 f., 116 f. Dual force of dividing cell, 26 f. Duboscq, Léger and, sexual process in Sarcocystis tenella, 108 n. Duerden, 261, 369 n., 371, 373, 374, 389, 397 n., 400 n., 403, 405, 406 Dujardin, on sarcode (= protoplasm), 3; on Protozoa, 45; on true nature of Foraminifera, 62 f.; on Sponges, 167 Dust, containing cysts of Protozoa, 47; of Flagellata, 118 Dysentery, in Swiss cattle, caused by Coccidium, 102; tropical, caused by Amoeba coli, 57 Dysteria, 137, 153; oral apparatus, 145; shell, 141

Earthworm, Monocystis parasitic in, 95 Echinanthidae, 549 Echinarachnius, 548, 549; E. parma, 542 f., 543, 544, 545, 547; shape, 542; sphaeridia, 545; internal skeleton, 545; habits, 546; alimentary canal, 546; Aristotle's lantern, 546; tube-feet, 547 Echinaster, 439, 462 Echinasteridae, 455, 458, 462 Echinating, 217 Echinidae, 539, 558 Echininae, 539 Echinocardium, 549; E. cordatum, 549 f., 551, 552; habitat, 549; shape, 550; spines, 550; sphaeridia, 551; alimentary canal, 551; tube-feet, 551; habits, 552; stone-canal, 552; E. flavescens, 555; E. pennatifidum, 555 Echinoconidae, 558 Echinocyamus, 548, 549; E. pusillus, 549 Echinocystites, 557 Echinodermata, 425 f. Echinoid stage in the development of a Holothuroid, 615 Echinoidea, 431, 503 f.; compared with Holothuroidea, 560; with Blastoidea, 580; mesenchyme of larva, 604; development of, 607, 608, 609, 613, 614; phylogeny of, 622 Echinolampas, 554 Echinometra, 542 Echinomuricea, 356 Echinoneus, 553, 553 Echinonidae, 553 Echinopluteus, 607, 608; metamorphosis of, 613, 614 Echinosphaerites, 598; E. aurantium, 598 Echinothuriidae, 530, 531, 532, 535, 558, 560 Echinus, 533, 539; E. esculentus, 504 f. 505, 507, 511-515; locality, 504; spines, 506; pedicellariae, 506; corona, 511; periproct, 513; peristome, 513; alimentary canal, 516; water-vascular system, 516 f.; nervous system, 518 f.; sphaeridia, 524; perihaemal spaces, 524 f.; genital system, 528; blood-system, 529; larva, 507; E. acutus, 540; pedicellariae, 509; E. alexandri, pedicellaria, 510; E. elegans, 539, 540; pedicellariae, 510; E. microtuberculatus, 540; E. miliaris, 540, 542, 549; E. norvegicus, 539, 540 Economic uses of Foraminifera, 69 f. Ectocoele, 367 Ectoderm, 246 Ectoplasm (= ectosarc), 6, 46 f., 50; of Amoeba, 5; of Rhizopoda, 51 f.; of Heliozoa, 71 f.; of Radiolaria, 79 f. (see also Extracapsular protoplasm); regeneration of, in Radiolaria, 35; of Collozoum inerme, 76; of Gregarines, 96 f.; of Ciliata, 141 f.; of Stylonychia, 140; of Suctoria, 159; of Trachelius ovum, 153; of Vorticella, 156 Ectopleura, 268 Ectosarc—see Ectoplasm Ectosome, 170 Ectyoninae, 217 Edrioasteroidea, 580, 596 Edwardsia, 328, 366, 368, 376; E. allmani, 377; E. beautempsii, 376, 377; E. carnea, 377; E. goodsiri, 377; E. tecta, 377; E. timida, 376, 377 Edwardsia stage of Zoantharia, 367 Edwardsiidae, 377 Edwardsiidea, 367, 371, 375, 395 Egg, fertilised, 31; of Metazoa, 32 f.; of bird, 32; various meanings of, 34; of affected Silkworm moths transmitters of pébrine, 107 Ehrenberg, on Protozoa, 45 f.; on skeletons of Radiolaria, 87 f.; on Ciliata, 146; on Suctoria, 162 Eimer and Fickert, on classification of Foraminifera, 58 n. Elasipoda, 569, 571, 577, 578 Electric, currents, stimulus of, 19, 22; shock, action on Amoeba, etc., 7 Eleutheria, the medusa of Clavatella, 265 Eleutheroblastea, 253 Eleutheroplea, 279 Eleutherozoa, 430, 560, 577, 579, 583; development of, 602 f.; larva of, 605; phylogeny of, 621, 622 Elevator muscles of compasses of Echinus esculentus, 527 Ellipsactinia, 283 Ellis, 167 Embryonic type of development, 601 Encystment, 37, 39; of animal cells, 37; of vegetal cells, 37, 39; growth during, 37; of zygote, general in Protista, 34; of Rhizopoda, 57; temporary, of Rhizopoda, 57 (see also Hypnocyst); of Heliozoa, 72 f.; of Actinophrys, 72; of Actinosphaerium, 73 f.; of Proteomyxa, 88, 89 of Myxomycete zoospores, 90 f.; of Sporozoa, 96 f.; of zygote of Sporozoa, 95 f.; of Gregarines, 95 f., 98; of Lankesteria, 95; of Monocystis, 96; of Coccidiidae, 97 f.; of Coccidium, 100, 101; of archespore or pansporoblast of Myxosporidiaceae, 107; of Flagellates, 115, 117 f.; of zygote of Bodo saltans, 117; of Opalina, 123 f.; of oosperm of Volvocaceae, 127 f., 129 f.; of Dinoflagellates, 131; of Ciliata, 147; of Colpoda cucullus, 147, 153 Endocyclica, 529, 530 f., 556, 559 Endoderm, 246 Endogamy, in Amoeba coli, 57; in Actinosphaerium, 73 f., 75 (diagram); in Stephanosphaera, 128 Endogenous budding in Suctoria, 160 f., 162 Endoparasitic Suctoria, 86, 160 f. Endoplasm (= endosarc, q.v.), 6 —see also Intracapsular protoplasm (Radiolaria) Endoral, cilia, 139; undulating membrane, 139 Endosarc (= endoplasm), 6; of Gregarines, 95 f.; branching, of Noctiluca, 110, 133; of Loxodes and Trachelius, 144, 153; of Ciliata, 143 f.; of Stylonychia, 140; of Suctoria, 161 Endosphaera, 159, 161 Energy, changes of, in living organism, 8, 13; sources of, 13 f. Entocnemaria, 394 Entocoele, 367 Entosolenia, 66 Entz, Geza, on Choanoflagellates, 121 n.; on structure of Vorticella, 157 n. Eocene Foraminifera, 70 Eolis (= Aeolis), 248 Eophiura, 501 Eozoon, 70 n. Epaulettes, 315 Epenthesis, 281 Ephelota, 159, 160; E. bütschliana, cytological study of, 162 Ephydatia, 217, 225; E. fluviatilis, structure, etc., 174 f., 176, 177, 178, 179 Ephyra, 317 Ephyropsidae, 322 Epiactis (usually placed in the order Zoanthidea, 404); E. marsupialis, 379; E. prolifera, 379 Epibulia, 308 Epidemic, of pébrine among Silkworms, 107; among Fish, due to Costia necatrix, 119; to Myxosporidiaceae, 107; to Icthyophtheirius, 152 —see also Diseases, Fever Epigonactis fecunda, 379 Epimerite of Gregarines, 97, 98 f. Epineural canal, of Ophiothrix fragilis, 481; of Echinus esculentus, 515 Epiphysis, of jaw, of Echinus esculentus, 526; of jaws of Diadematidae, 531; absent in Cidaridae and Arbaciidae, 531 Epiphytic Protozoa, 48 Epiplasm (= cytoplasm of a brood-mother-cell remaining over unused in brood-formation), 96 Epistrelophyllum, 403 Epistylis, 138, 158; E. umbellaria, nematocysts of, 249 Epitheca, 386 Epizoanthus, 406; on Hyalonema, 204; E. glacialis, infested by Gregarines, 99; E. incrustatus, 406; E. paguriphilus, 406; E. stellaris, 406 Epizoic, Protozoa, 48; Ciliata, 158; Suctoria, 158, 162 —see also Symbiosis Equatorial plate (= the collective chromosomes at the equator of the spindle in mitosis), 25, 27 Equiangular, 185 Errina, 284, 286; E. glabra, 286; E. ramosa, 286 Ersaea, 306; E. picta, 303 Esperella, 225, 231 Esperiopsis, 225 Euaster (a true aster in which the actines proceed from a centre, contrasting with the streptaster), 184 Eucalyptocrinus, 596 Eucharidae, 420 Eucharis, 420; E. multicornis, 416, 418 f., 420 Enchlora, 417 Eucladia, 502 Euclypeastroidea, 549 Eucopidae, 277, 280 Eudendrium, 269, 270 Eudiocrinus, 594 Eudorina, 111, 128 f. Eudoxia, 306; E. eschscholtzii, 303 Euglena, 110; barotaxy of, 20; nutrition of, 113; E. viridis, 124 Euglenaceae, 110, 124; pellicle of, 113 Euglenoid motion, 124; of Sporozoa, 50 Euglypha, 52; in fission, 29; test, 29, 54 Eunicea, 356; spicules, 335, 336 Eunicella, 356; spicules, 335, 336; E. cavolini, 356 Eupagurus prideauxii, 378, 381; E. bernhardus, 378 Eupatagus, 553 Euphyllia, 401 Euplectella, 204; E. aspergillum (Venus's Flower-Basket, 197); E. imperialis, 206; E. suberea, 202, 204, 205, 221 Euplexaura, 356 Euplokamis, 418 Euplotes, 138 Eupsammiidae, 402, 404 Eurhamphaea, 419 Eurhamphaeidae, 419 Euryalidae, 501 Eurypylous, 210 Euspongia, 221 Eutreptia, 110; E. viridis, 124 Evacuation of faeces by mouth in Noctiluca, 133 Evans, 179 n., 217 Excretion, 13 f.; in Sponges, 172; in Asterias rubens, 437; in Echinus esculentus, 527, 528; in Antedon rosacea, 587 Excretory, granules, 6; of Ciliata, 144; pore of contractile vacuole of Flagellates, 110; of Trachelius ovum, 153 Exogametes of Trichosphaerium, 54 Exogamy, 34 n.; in Rhizopoda, 56 f.; in Foraminifera, 68 f. Expansion of Amoeboid cell, 16 f. Exsert, septa, 398, 399 Extracapsular protoplasm, of Phaeodaria, 76; of Radiolaria, 79 f. (see also Ectoplasm) Eye of Asterias, 445 f., 446; of Echinoidea, 512 Eye-spot of coloured Protista, 21, 125 f.

Fascicularia, 348 Fasciole, of Echinocardium, 550, 555; of Spatangoidea, 553; of Spatangus, 553; of Eupatagus, 553; of Spatangidae, 555 Fats, fatty acids, 15; in Flagellates, 110, 115; formation of, 36 Fauré-Fremiet, on attachment of Peritrichaceae, 141 n. Faurot, 368 Favia, 373, _401 Favosites_, 344 Favositidae, 344 Feather-star, 581 Feeding, of Noctiluca, 133, 144; of Peritrichaceae, 145 —see also Food Feeler, of Holothuria nigra, 561 f., 566; of Holothuroidea, 568; of Dendrochirota, 568, 572; of Synaptida, 568, 575; of Molpadiida, 568, 575 Female gamete, 33; of Pandorina, 128 f.; of Acystosporidae, 104 f.; of Peritrichaceae, 151, 157 —see also Megagamete, Oosphere Ferment, required for germination, brood-formation, etc., 32 f. —see also Zymase Fermentation, organisms of, 43 f. Fertilisation, 33 f.; "chemical," 32 n. Fertilised egg, 31 —see also Oosperm, Zygote Fertilising tube of Chlamydomonas, 125 Fever, intermittent, malarial, 103 f.; relapsing, 121; remittent, 105; Texas-, Tick, 120; Trypanosomic, 119 f. Fewkes, 268 n. Fibularidae, 549 Fibularites, 559 Fickert, Eimer and, on classification of Foraminifera, 58 n. Ficulina, 219, 224, 230; F. ficus, 219 Filoplasmodieae, 90 f. Filopodia, 47 n. Filosa, 29, 50, 52 f.; resemblance to Allogromidiaceae, 59 Finger, 580; of Cystoidea, 597; of Blastoidea, 599, 600 Firestone of Delitzet contains fossil Peridinium, 132 Fischer, on fixing reagents, 11; on structure of flagellum, 114 Fish, rheotaxy of, 21; epidemics of, due to Myxosporidiaceae, 107; to Costia necatrix, 119; to Ichthyophtheirius, 152 Fission, 10, 23 f.; equal, 10; Spencerian, 23; multiple, 30 f. (see also Brood-division); of Heliozoa, 72 f.; of Radiolaria, 84 f.; radial, in Volvocaceae, 110; transverse, in Craspedomonadidae, 115 n.; longitudinal and transverse, of Bodo saltans, 117; of Opalina, 123; of Euglenaceae, 124; of Eutreptia viridis, 124; of Noctiluca, 133; of Ciliata, 147 f.; of Stentor polymorphus, 156; of Vorticellidae, 157 f. —see also Bud-fission Fissiparantes, 387, 400 Fixing protoplasm, 15 Flabellum, 375, 386, 398; protandry of, 370 Flagella, flagellum, 17 f., 47; of Protozoa, 47; formed by altered pseudopodia in Microgromia, 60; of Heliozoa, 73; of sperms of Coccidiidae, 102; of Acystosporidae, 105; of Flagellata, 109, 114 f.; of Trichonymphidae, 114; Delage on mechanism of, 114 n.; of Bodo saltans, 117; of Trypanosoma, 121; of Euglenaceae, 124 f.; of Maupasia, 124; of Eutreptia viridis, 124; of Sphaerella, 126; of Dinoflagellata, 130, 131; of Peridinium, 131; of Polykrikos, 132; of Noctiluca, 132, 133 f. —see also Sarcoflagellum Flagellar pit, in Flagellates, 110, 124 f. Flagellata, 17 f., 40, 48 f., 50, 109 f.; barotaxy of, 20; galvanotaxy of, 22; chemiotaxy of, 23; nutrition of, 40, 113; of putrefying liquids, 44, 116 f.; studied by botanists, 45; as internal parasites, 48, 119 f.; relations with Acystosporidae, 106; shell of, 113; stalk of, 113; life-history of, 116 f.; literature of, 119; saprophytic, 119 f. Flagellate stage, of Sarcodina, 56 f., 60, 109; of Heliozoa, 74; of Radiolaria, 85 f. —see also Flagellula Flagellated chamber, 170 Flagellula, 31; of Proteomyxa, 88, 89; of Myxomycetes, 91, 92; of Didymium, 92 —see also Zoospores Flagellum—see Flagella Fleming, 168 n. Flexible Corals, 326 Flint, 219, 241 Floricome, 203 Floscelle, of Echinocardium cordatum, 551; of Cassidulidae, 554 Flowering plants, male cells of, 38 Flowers of tan (= Fuligo varians), 92 f.; peptic ferment in, 16 Foam structure, 6 Folliculina, 137; tube of, 152 Food, 35 f. (see also Ingestion); of Higher Animals, 38; absorption of, by Plants, 38; in relation to life-cycle of Ciliata, 147 f.; of Sponges, 237; of Hydra, 256 and n.; of Millepora, 261; of Siphonophora, 304; of Charybdea, 319; of Alcyonium, 339; of Zoantharia, 373; of Asterias rubens, 439; of Ophiothrix fragilis, 486; of Ophiolepididae, 496; of Echinus esculentus, 516; of Echinarachnius parma, 546; of Echinocardium cordatum, 552; of Holothuria nigra, 561; of Dendrochirota, 572; of Synapta inhaerens, 577; of Antedon rosacea, 583 Food-vacuole, of Actinosphaerium eichornii, 72; of Ciliata, 145 f.; of Carchesium, 146 Foot-plate, of young Pentacrinidae, 592; of larva of Antedon rosacea, 619 Foraminifera, 40, 49, 50, 58 f.; relations of, 49; shell of, 49, 59 f., 60, 61, 63, 65; habitat of, 59 f.; literature of, 58 n.; marine, 60 f.; nuclei of, 62, 67 f.; nutrition of, 40, 62; streaming of granules in, 17; chromidia of, 62, 68 f.; collection of, 62; dimorphism of, 66, 67; reproduction of, 67 f.; economic uses of, 69 f.; palaeontology of, 69 f. Forbes, 338 Force, dual, of dividing-cell, 26 n. Forcepia, 223 Forceps, 222 Forcipulata, 462, 473 f. Forcipulate pedicellaria, 456, 473 Formative vacuole of contractile vacuole, in Flagellata, 110, 115; in Ciliata, 143 Fossil, Foraminifera, 69 f.; Radiolaria, 87 f.; Dinoflagellata, 132; Peridinium, 132; Sponges, 192 f., 207 f., 215, 241; Coelenterates, 270, 281 f., 343 f., 346, 393 f., 406; Asteroidea, 475 f.; Ophiuroidea, 501 f.; Echinoidea, 556 f.; Crinoidea, 594 f.; Thecoidea, 596; Carpoidea, 596 f.; Cystoidea, 597 f.; Blastoidea, 599 f. Fowler, 293 n., 382, 400, 404 Framboesia, 121 n. France, epidemic of pébrine in, 107 Francé, on structure of funnel of Choanoflagellates, 115 n., 121 n.; monograph of Choanoflagellates, 123, 182 n.; on Polytomeae, 119 n. Freetown, prophylaxis of malaria at, 106 Fringing reef, 390 f. Frog's blood, Lankesterella in, 102 Frondicularia, 59, 63 Fructification, of Mycetozoa, 90 f.; of Acrasieae, 90; of Myxomycetes, 49, 91 f. Fry, E. and A., on Myxomycetes, 93 n. Fuligo, 90; F. varians, 92 f.; pepsin in, 16 Fungacea, 402 Fungi, cell connexions in, 37 f.; in relation to Protista, 40; Gasteromycetous, 91 Fungia, 403; asexual reproduction of, 388, 389; F. crassitentaculata, 403 Fungiidae, 403 Funiculina, 359, 362; F. quadrangularis, 362 Funiculinidae, 362 Funnel, of Craspedomonadidae or Choanoflagellates, 111, 121, 122, 182; of Phalausteridae, 111; of choanocytes of Sponges, 171 Fusion of larval Sponges, 174 Fusion-nucleus of Ciliata, 150 —see also Reproduction, Syngamy, Zygotonucleus Fusulina, 59

Galaxea, 400; G. esperi, 400 Galeolaria, 307; G. biloba, 304 Galeolarinae, 307 Galerites, 558 Gamble, 312 n.; and Keeble, 175 n. Gametes, 33 f.; of Trichosphaerium, 54; of certain Protomastigaceae, 116 n.; of Volvocidae, 127 f.; of Pandorina (of three sizes), 128, 129 Gametocyte of Acystosporidae, 104 f. Gametogonium (= parent-cell of gametes), male, of Acystosporidae, 105 Gametonuclei (= nuclei capable of syngamous fusion), 34 Ganeria, 464 Ganeriidae, 454, 464 Gardiner, 345, 370, 375, 392 n., 404 Garveia, 270 Gasteromycetous fungi, 91 Gastral layer, 171 Gastralia, 201 Gastropores, 257, 258 Gastrozooids, of Millepora, 259, 260; of Hydractinia, 264; of Siphonophora, 299; of Antipatharia, 408 Gastrula, definition of, 603 Gaule, misinterpretation of nature of Haemosporidae, 102 Gegenbaur, 302 Gellius 217, 223; G. varius, development, 172 f., 173, 174 Gemmantes, 400 Gemmaria, 405 Gemination = Budding, q.v. Gemmiform, pedicellariae, of Echinus esculentus, 506; of E. acutus, 509; of E. elegans, 510; of Cidaridae, 534; of Echinarachnius parma, 544; of Echinocardium cordatum, 550 Gemmule, 177, 178, 179, 230 Generation, spontaneous, 42 f. Generations, alternation of, 44, 250 Genital base of Holothuria nigra, 567 Genital bursa, of Ophiothrix fragilis, 485 compared with hydrospires of Blastoidea, 600 Genital canal of Antedon rosacea, 586 Genital organs (including ducts), of Asterias rubens, 451 f.; of Ophiothrix fragilis, 490; of Ophiarachna, 491; of Ophiuroidea, 494; of Amphiura squamata, 494; of Echinus esculentus, 528; of Echinocardium cordatum, 552; of Hemiaster philippi, 552; of Holothuria nigra, 567; of Antedon rosacea, 586 Genital plate, of Ophiothrix fragilis, 485; of Echinus esculentus, 512, 513 Genital rachis, of Asterias rubens, 452; of Ophiothrix fragilis, 490; of Echinus esculentus, 528; of Antedon rosacea, 586 Genital scale of Ophiothrix fragilis, 485 Genital stolon, of Asterias rubens, 451; of Ophiothrix fragilis, 489; of Echinus esculentus, 528; of Holothuria nigra, 567; of Antedon rosacea, 585, 586; of larva of A. rosacea, 619 Geodia, 211 Geographical distribution of Protozoa, 47 Geotaxy (= barotaxy), 20 Gephyra dohrnii, 382, 408 Gephyrea, 577 Gerarde, 167 Gerardia savalia, 406 Gerbillus indicus infested by a Haemosporidian, 102 n. Germinal spot (= nucleole of ovum), 7 Germinal vesicle (= nucleus of ovum), 7 Germination, 32; of Myxosporidian spores, 107 Germ-plasm, 28 f.; continuity of, 172 Germ theory, 44 Germs, invisible air-borne, 43 Geryonia, 290, 295 Gilchrist, 338 Gill of Echinus, 514, 527 Gill-cleft, of Echinus, 514; of Sphaerechinus, 540 f.; of Strongylocentrotus, 541 Ginkgo, spermatozoa of, 38 Glaucoma, 137, 153; G. scintillans, rate of fission of, 147 f. Glauconite, 70 Globiceps, 272 Globiferae of Centrostephanus longispinosus, 532 Globigerina, 59, 63, 242; spines of, 61, 66; -ooze, 61 f.; G. bulloides, 68, 69 Glossina morsitans, intermediate host of Trypanosoma brucei, 119; G. palpalis, intermediate host of T. gambiense, 120 Glossograptus, 282 Glycerin, 15 Glycogen, of Ciliata, 144; -vesicles of Pelomyxa palustris, 53 Gnat (Anopheles), intermediate host of Haemamoeba and Laverania, 103 f.; (Culex) intermediate host of Haemoproteus, 103; of Trypanosoma, 120 Golgi, on relation of Acystosporidian life-cycle and stages of intermittent fever, 103 Gonactinia, 371, 372, 377 Gonangium, 276 Goniaster, 471; fossil, 475 Goniastraea, 375, 401 Goniocidaris, 534; G. canaliculata, 535 Gonionema, 288, 291; G. murbachii, 232, 290, 291, 292 Gonium, 111 Gonophore, of Gymnoblastea, 265; of Calyptoblastea, 277; of Stylasterina, 284; of Siphonophora, 302 Gonotheca, 276, 281 Gonozooids, of Siphonophora, 302; of Antipatharia, 408 Gorgonacea, 350 f. Gorgonella, 357; spicule, 336 Gorgonellidae, 337, 357 Gorgonia, 356; G. cavolinii, 340; G. flabellum, 357; G. verrucosa, 356 Gorgoniidae, 334, 337, 356 Gorgonocephalus, 491, 501 Gosse, 273 Goto, 291, 293; on development of Bipinnaria, 612 Grammaria, 278 Granatocrinus, 599; G. norwoodi, 600 Grant, 167 Grantiidae, 192 Grantiopsis, 191 Granular disintegration of Protista, 14 f. Granules, in protoplasm, 6; excretory, 6, 144; aleurone, 37; basal, of cilia, etc., 138 n., 141 (see also Blepharoplast); proteid, of Suctoria, 161 Graphiohexaster, 203 Graptolitoidea, 281 Grassi, on malarial parasites, 103 Gravity, stimulus of, 19 f. Greasy film, outer clear layer of protoplasm behaves like, 17 Greeff, on Protozoa, 46 Green Flagellates, relations of, 48 Greensand, 70; Cambridge, 208 Green water often due to Euglena viridis, 124 Greenwood, M., on peptic digestion in Protozoa, 16; on feeding of Carchesium polypinum, 45 f., 146 f. Gregarina, 97, 98, 99; G. blattarum, 98 Gregarines, habitat, 99; syngamy, 99 Gregarinidaceae, 95 f., 97 f. Gregory, 346 Grew, 166 Grey chalk, 61 Gromia, 52; G. oviformis, 59 n. —see also Allogromia Grooves, longitudinal and transverse, of Dinoflagellata, 110, 130, 131, 132; of Peridinium, 131; of Polykrikos, 132; oral, of Noctiluca, 133 Grosvenor, 249 n. Growth, 19 f.; Spencer's limit of, 23, 31 Gruber, on regeneration in Protozoa, 35 n.; on diffused nucleus in marine Ciliata, 144 n.; on tubicolous marine Ciliata, 152 Gruppe, deposit of Radiolaria, 87 Guinea Coast, 106 Gullet (= pharynx) of Paramecium caudatum, 151 Gut, supposed, of Ciliata, 145 —see also Alimentary canal Gutter, oral, of Vorticellidae, 156, 158 Gymnamoebae, 51 n. Gymnasteridae, 471 Gymnoblastea, 262 f. Gymnodinium, 110; G. pulvisculus, parasitic in Appendicularia, 132 Gymnomyxa, 49 n. Gymnophrys, 58 Gymnosphaera, 70, 73 Gymnostomaceae, 137; predaceous, trichocysts of, 143; mouth and pharynx of, 145; noteworthy members of, 152 Gyractis, 380

Häcker, on skeleton of Radiolaria, 82 n. Haddon, 382 Haeckel, 168, 185, 192, 237, 308; on Monera, 4 n., 89 n.; on Protista, 40 f.; on Protozoa, 46; on Heliozoa, 71; on classification of Radiolaria, 76; on functions of porocone in Radiolaria, 81; on enumeration of Radiolaria, 87 f.; on Myxobrachia, 83; on Sponges, 168, 192; on phylogeny of Echinodermata, 622 Haeckeliana, 79, 85 Haemamoeba, 97, 103 f.; H. malariae, parasite of quartan fever, 104 f.; H. vivax, parasite of tertian fever, 104 f. Haematochrome, 125 Haematococcus (= Sphaerella, 111), 125, 126 Haemoflagellates (= Trypanosoma, etc., q.v.), 119 n. Haemoglobin, 103; in water-vascular system of Ophiactis virens, 499 Haemogregarina, 97 Haemomenas (Ross's name for parasite of pernicious fever = Laverania, 97), 105 Haemoproteus, 97; parasitic in birds, 103 Haemosporidae, 97, 102 Haimea hyalina, 342; H. funebris, 342. Haimeidae, 342 Halcampa, 366, 380; H. chrysanthellum, 380 Halcampidae, 375, 380 Halecium, 277, 280 Haleremita, 256 Halicalyx, 291 Halichondria, 217, 223; H. panicea, structure, etc., 168 f., 169, 170, 211 Halichondrina, 216, 217 Haliclystus, 320, 321; H. auricula, 320 Halicnemia, 216, 224 Haliomma, 77 Haliphysema, 59 Halisarca, 196, 225 Halomitra, 404 Halteria, 137, 152, 155 Halteridium, 97; sexual fusion in, 103, 105; regarded by Schaudinn as a state of Trypanosoma, 103 n., 120 Hamacantha, 223 Hamann, on supposed cavities in the body-wall of Asteroidea, 449; on classification of Zygophiurae, 495 n. Hanitsch, 168 n. Hapalocarcinus, 402 Hardy, on structure of protoplasm and clearing, 11, 12 n. Hartea elegans, 342 Hartlaub, 269 n., 274, 297 n. Hartog, on Protozoa, 1 f.; on structure of protoplasm, living and dead, 11; on function of contractile vacuole, 15 n.; on intracellular digestion, 16; on brood-division (multiple cell-division), 16 n.; on dual force of dividing cell, 26 n.; on syngamy, etc., 34 n.; and Dixon, on pepsin in Pelomyxa, 16 Harvey, "omne vivum ex ovo," 42 Hastigerina, 59, 66 Hauerina, 59 Heart, of Asterias rubens, 450 Heart-urchins = Spatangoidea, q.v. Heat—see Temperature Heat-rigor, 22 Heleopera, 52; test of, 55 Heliaster, 474 Heliasteridae, 453, 454, 474 Heliolites, 346 Heliolitidae, 346 Heliopora, 330, 334, 337, 345 f. Helioporidae, 346 Heliozoa, 50, 70 f.; streaming of granules, 17; regeneration, 35; habitat, 48; locomotion, 73; various forms of, 74; marine, 75; distribution of, 75; resemblance of Suctoria to, 159 Hemiaster, 556; H. philippi, 552, 555, 602, 603 Hemichordata, 616 Henneguy, on protoplasm, 3 n.; on syngamy, 34 n. Henneguya, 98 Henricia—see Cribrella Hérouard, Delage and, on Protozoa, 46 Herpetolitha, 404 Herpetomonas, 115 Hertwig, R., on Protozoa, 46; on chromidia in Sarcodina, 52 n.; on Heliozoa, 71; on Radiolaria, 88; on Suctoria, 161 n., 162 Heteractinellida, 208 Heterastridium, 283 Heterocentrotus, 532, 542 Heterocoela, 187 f. Heterophrys, 71 Heteropidae, 192 Heterotrichaceae, 137, 153 f.; fission of, 147 Heteroxenia, 333, 335, 348 Hexactine (a triaxon in which all six actines are developed), 184 Hexactinellida, 194, 195, 197 f., 228, 240 Hexadella, 196 Hexamitus, 115 Hexaster (a hexactine with secondary or terminal rays = Carter's "rosette"), 203 Hexasterophora, 203 f. Hickson, on interchange of cytoplasm in conjugating Infusoria, 149 n.; on conjugation in Suctoria, 161 f.; on Coelenterata, 243 f.; on Millepora, 259 n.; on Stylasterina, 286 n.; on Alcyonaria, 329 n., 351 n., 352 n., 359 n.; on Antipatharia, 408 n.; on Ctenophora, 412 f. Hieronymus on Chlamydomyxa, 90 n. Hincks, 268 n. Hinde, 193, 207 Hippasterias, 471 Hippopodius, 307 Hippospongia, 221 Holectypoidea, 558 Holophytic, Algae and Fungi, zoospores of, 5; nutrition, 37; Flagellates, 113 Holopodidae, 592 Holopus, 588, 589, 594 Holothuria, 570; H. nigra, 561 f.; shape, 561; feelers, 561; body-wall, 562; alimentary canal, 562; respiratory trees, 563; water-vascular system, 564; nervous system, 566; calcareous ring, 566; blood system, 567; genital organs, 567; H. cinerascens, 567; H. fusco-rubra, 567; H. aspera, 570; H. intestinalis, 570; H. tremula, 570 Holothuroidea, 431, 537, 560 f., 583; mesenchyme of larva, 604; development of, 609, 614, 615; phylogeny of, 622 Holotrypasta (= Porulosa), 76 Holozoic, 35 f.; Flagellates, 113; Dinoflagellates, 131 Holt, 311 n.; on burrowing habits of Strongylocentrotus lividus, 541 n. Homaxonic (= symmetrical about a centre along an indefinite number of equivalent axes), 76 Homocoela, 185 f. Homoeonema, 294 Homostichanthus anemone, 383 Honey-bees, alleged spontaneous generation of, 42 Hormiphora, 418; H. plumosa, 413 Human diseases, produced by Coccidiaceae, 102 f.; by Amoeba histolytica, 57; by Trypanosomids, 119 f. Huxley, on Protozoa, 45; first description of a living Radiolarian, 88; on Cystoflagellates, 135 Hyalonema, 203, 204; H. sieboldi, 206; H. thomsoni, 204, 221 Hyalopus, 52; H. dujardini, 59 n. Hyalosphenia, 52; H. lata, 55 Hyboclypus, 558; H. gibberulus, 558 Hybocodon (Corymorphidae, 273), 265 Hydatina senta, often found with Euglena viridis, 124 Hydra, 253 f., 255; nematocysts of, 247; species of, 256; specific gravity of, 13 n.; host of Kerona and Trichodina, 158; Zoochlorella in, 126, 256; H. oligactis (= fusca), 253, 256; H. pallida, 256 n.; H. viridis, 253, 256; H. vulgaris, (= grisea), 253, 256; nematocyst, 247 Hydractinia, 263, 265, 268, 270 Hydrallmania falcata, 278 Hydrichthys mirus, 268 Hydroceratinidae, 279 Hydrocladia, 276 Hydrocoel (including left hydrocoel), 428; of Antedon rosacea, 585; development of, 608 f., 609; development in Asterina gibbosa, 611; in Auricularia, 615; in Antedon rosacea, 619 Hydroctena salenskii, 423, 424 Hydrolaridae, 273 Hydrophyllium, 297, 300 Hydrorhiza, 262 Hydrosome, 250, 251 Hydrospire, of Blastoidea, 580, 599; of Codaster, 599; of Pentremites, 599; of Granatocrinus, 599 f. Hydrotheca, 275 Hydrozoa, 249 f.; hydrosome, 250; life-history, 250; medusome, 250, 251 f.; sense-organs, 252 Hydrurus, 110; theca of, 113 Hymedesmia, 222 Hymenaster, 466; H. pellucidus, 465 Hymeniacidon, 224 Hymeraphia, 223 Hyocrinidae, 590 Hyocrinus, 588, 589, 590, 590; H. bethellianus, 590 Hyperia (Amphipod), parasitic in Radiolaria, 87 Hyphalaster, 471; H. moseri, 459 Hypnocyst, of Rhizopoda, 57; of Proteomyxa, 88 f.; of Pseudospora, 89; of Myxomycetes, 90 f. Hypolytus peregrinus, 262, 271 n. Hypophare, 210 Hypostome, 250 Hypotrichaceae, 137, 138 f., 158 n.

Ianthella, 220 Ichthyophtheirius, 137; noxious parasite of fish, 152 Iciligorgia, 351 Idioplasm, 29 Ijima, 199, 206, 231, 234 Ileonema, 137, 152 Ilyanthus mitchellii, 380 Ilyodaemon, 571, 572; I. maculatus, 571 Imperforate, Foraminifera, 58 f.; Corals, 371 Inadunata, 595 Incurrent canal, 170 India, diseases of Trypanosomic origin, 119 f. Induction shocks, action on Protozoa, 7, 22 Infero-marginal ossicle of Asteroidea, 436 Inflammation, 8 Infra-basal plate, of Crinoidea, 588; of fossil Crinoidea, 594; of larval Antedon rosacea, 619 Infundibulum, 415 Infusions, appearance of organisms in, 42 f.; organisms of, 136 Infusoria, 40, 48, 50, 136 f.; specific gravity of, 13 n.; zygote does not encyst, 34. Ingestion, of food, by Amoeba limax, 9; by Choanoflagellates, 122; by Dinoflagellates, 131; by Carchesium, 146; by Coleps, 150 —vacuole of, in Flagellates, 113; in Oikomonas, 112; in Choanoflagellates, 122 Inner perihaemal ring-canal, of Asterias rubens, 448; development of, in Asterina gibbosa, 612 Inoculation of malarial fever in man through a mosquito, 105 f. Insectivorous plants, 38 Insects, metamorphoses of, 44; as hosts of Trichonymphidae, 123 Interambulacral area, of Echinarachnius parma, 544; of Echinocardium cordatum, 550 Interambulacral plate, of Echinus esculentus, 511; of Cidaridae, 533 f.; of Echinarachnius parma, 544 f. Interbrachial septa—see Interradial septa Interchanges between cell and medium, 14 Intermediate dorsal process of ciliated band of Auricularia, 608 Intermediate (= supplemental) skeleton of Perforate Foraminiferal shell, 63, 66 Intermittent fever, malarial, produced by Acystosporidae, 103 f. Internal budding of Suctoria, 160 f., 162; of Ephydatia, 177 Internal gills—see Stewart's organs Internal movements of protoplasm, 17 Interradial plates, of calcareous ring of Holothuria nigra, 566; of Holothuroidea, 569; of Synaptida, 569; of Dendrochirota, 569; of calyx of Crinoidea, 589; of Thaumatocrinus, 589; of Hyocrinus, 590; of Rhizocrinidae, 591; of corona of Echinoidea—see Interambulacral plate Interradial septa, of Asterias rubens, 437; of Heliasteridae, 474; absent in Brisingidae, 475 Interradius, 428; of Asterias rubens, 434; of Echinus esculentus, 504; of Holothuria nigra, 562 Interstitial growth, 10 Intestine, 415; of Echinus esculentus, 516; of Holothuria nigra, 563; of Antedon rosacea, 583; of Actinometra, 589; of Dipleurula, 605; of Protocoelomata, 616 Intracapsular protoplasm of Radiolaria, 80 f. Intramolecular respiration, 14 n. Intranuclear spindle of Euylypha, 29 Invertebrata, hosts of Gregarines, 97 f. Iodine, 239 Iophon, 223 Iridogorgia, 355 Isaurus, 405 Ischadites, 207 Ischikawa, on syngamy of Cystoflagellates, 135; on structure of Ephelota, 162 Isidae, 337, 353 Isidella, 354 Isis, 353 Ismailia, prophylaxis of malaria at, 106 Isochela (a chela divisible by each of two planes into two equal parts, the two ends being equally developed), 222 Isocrinus—see Pentacrinus Isogamy, 33 f.; of Rhizopoda, 56 f.; of Stephanosphaera, 128 —see also Syngamy Isospores, 85; of Radiolaria, 76; of Collozoum inerme, 76

Jaekel, on Silurian Asteroidea and Ophiuroidea, 501; on classification of Crinoidea, 589, 595; on classification of Cystoidea, 598 James-Clark, on Protozoa, 46; on Choanoflagellates, 121, 123; on Sponges, 167 Jaw, of Ophiothrix fragilis, 482; of fossil Ophiuroidea, 502; of Echinus esculentus, 526 Jelly, forming theca in Flagellates, 113 Jelly-fish, 249, 297, 323 Jennings, on protoplasmic movements, 4 n., 16 n.; reaction of Protista to repellent stimuli, 20 n., 21 n. Jensen, on density of living protoplasm, 13 n.; on protoplasmic movements, 16 n. Joblot, on organisms of putrefaction, 43; on Protozoa, 45 Joenia, 111 Johnson, 352 n. Juncella, 330, 335, 357 Jung, 253 n. Jungersen, 359 n.

Karyogamy, 34 n. —see also Syngamy of Ciliata Karyokinesis, 25, 26, 27; function of, 28 f.; of micronuclei of Ciliata, 144 f. —see also Mitosis Karyolysus, 97 Karyosome, 24 Keeble, 175 n. Keller, 233 Kemna, on stylopodium of Foraminifera, 60 Kent, Saville, on Choanoflagellates, 122 f., 182; on Infusoria and Flagellates, 136 n. Keroeides, 351 Kerona, 138; K. polyporum, 158 n. Kieselguhr, 87 Kirkpatrick, 215 Kishinouye, 313 n., 321 n., 333, 352 Klebs, on Flagellates, 119; on Dinoflagellates, 130 Koch, von, on methods of cultivation of lower organisms, 44; on malarial parasites, 103 Kölliker, on Sporozoa, 94 f. Kophobelemnon, 362 Kophobelemnonidae, 362 Köppen, on Sticholonche and its parasite, Amoebophrya, 87 n. Korethraster, 453, 463 Kowalevsky, 341, 422 Krukenberg, on pepsin in a Myxomycete, 16 Kükenthal, 363

Labbé, on Protozoa, 45; monograph of Sporozoa, 102 n. Labial plexus of Antedon rosacea, 587 Labyrinthine shell-wall of arenaceous Foraminifera, 59, 66 Labyrinthula, 90 f. Lachmann, Claparède and, on Protozoa, 45; on Suctoria, 162 Lacrymaria, 137, 152 n.; encystment, 147 Lafoea, 280; L. dumosa, 280 Lafoëina (Campanulariidae, 280), 277 Laganum, 548, 549 Lagena, 59, 63, 66 f.; fossil, 70 Lagenaceae, 59 Lagoon, 390 f. Lamblia, 111; L. intestinalis, conjugation, 116 n. Lampetia, 418 Lancet-plate, 599 Lang, on syngamy, etc., 34 n.; on Protozoa, 46; on distinctions of pseudopodia, 47 n. Lankester, on Protozoa, 45 f.; on classification of Protozoa, 49 n.; on Proteomyxa, 89; on Sporozoa, 94; on Haemosporidae, 102; on pigment of Stentor coeruleus, 154 n.; on Torquatella, 155 n.; on chlorophyll of Ephydatia, 175; on Limnocodium, 292 Lankesterella, 97, 102 Lankesteria, 97; L. ascidiae, life-cycle of, 95 Lantern-coelom of Echinus esculentus, 524; represented by buccal sinus of Holothuria nigra, 566 Lanuginella pupa, 198 Lar, 273; L. sabellarum, 266, 267, 268 Larcoidea, 77 Larva, of sponges, 180, 226, 227; "asexual," 228; of Tubularia, 271; of Stylasterina, 284; of Trachomedusae, 290; of Narcomedusae, 295; of Velella, 302; of Scyphozoa, 317; of Alcyonaria, 341; of Renilla, 360; of Zoantharia, 373; of Zoanthidae, 405; of Cerianthidea, 411; of Ctenophora, 416, 419; of Cribrella, 462; of Luidia, 605; of Asterina gibbosa, 463, 610, 611, 612; of Ophiuroidea, 606; of Echinus, 607; of Synapta, 608; of Antedon rosacea, 618, 619, 620 Larval brain, of Echinopluteus, 607; of Antedon rosacea, 619 Larval type of development, 601 Lateral mouth-shields of Ophiothrix fragilis, 485 Lauterborn, on sapropelic organisms, 48; on budding in Rhizopods, 56 n. Laveran, on Sporozoa, 94; on Acystosporidae, 102 Laverania, 97; parasite of bilious or pernicious fever, 104 f. Lebrunia, 382; L. coralligens, 373 Lecqueureusia, 52; L. spiralis, test of, 55 Lee, A. Bolles, on action of clearing reagents, 11 n. Leech, host of Haemogregarina, for sexual process, 102 Leeuwenhoek, on organisms of putrefaction, 42 f. Léger, on Protozoa, 45; on Sporozoa, 94; on sperms of Pterocephalus, 99 n.; and Duboscq, on Sarcocystis tenella, 108 n. Leidy, on Protozoa, 46 Leiopathes, 368, 409 Leiopathidae, 409 Leiosella, 225 Leipoldt, on the madreporic vesicle of Echinoidea, 528 Lelapia australis, 192 Lembadion, 137; caudal cilia of, 141 n. Lembus, 137; caudal cilia of, 141 n. Lemnalia, 349 Lendenfeld, von, 218, 220, 220 n. Lepidogorgia, 355 Leptobrachiidae, 325 Leptodiscus, 110, 132, 134 Leptogonaster, 456, 467 Leptogorgia, 340, 357 Leptopenus, 404 Leptophyllia, 404 Lesser, Hertwig and, on Heliozoa, 71 Lesueuria, 419 Lesueuriidae, 419 Leucandra, 191, 192, 209, 221 Leucilla, 191, 191 Leucin, 15 Leuckart, 245 Leucocyte, 4 f.; movements of, 7 f. Leucophrys, 137 Leucosin, 115 Leucosolenia, 221; collar-cell, 186; larva, 227 f.; spicule, 232; L. botryoides, buds, 228, 229 Leucosoleniidae, 185 f. Levander, on Caenomorpha, Metopus, etc., 154 n. Leydenia, 90 f. Liberation of sporozoites of Acystosporidian parasite in relation to fits of fever, 103 Lice, supposed spontaneous generation of, 42 Lichen compared to Radiolarian with symbiotic holophytic organisms, 86 Lichnophora, 138; adoral wreath, 138 n. Lieb, Calkins and, on rhythm in life-cycle of Ciliata, 148 n. Lieberkühn, 167, 178, 237 n. Lieberkühnia, 59, 61 Life-cycle, life-history, of Trichosphaerium sieboldi, 54, 56; of Polythalamic Foraminifera, 67 f.; of Lankesteria ascidiae, 95 f.; of Coccidium schubergi, 99 f., 101; of malarial parasites, 103, 104 f.; of Flagellata, 116 f.; of Ciliata, 147 f. Light, stimulus of, 19, 21 f.; function of, in carbohydrate formation, 36; effect on Euglena, 125 Lillie, on regeneration in Protozoa, 35 n. Limicolous Protozoa, 48 Limit of growth, Herbert Spencer's, 23 f., 31 Limnocnida, 293; L. tanganyicae, 293 Limnocodium, 293; L. sowerbyi, 292 Linantha, 322 Linckia, 459, 471 Linckiidae, 461, 471 Lindström, 346 Linerges (allied to Atollidae, 322), 316 Linin, 6, 24 f.; of ovum of Sea-urchin, 7 Linuche, 322 Lionotus, 137, 152 n. Lipochrome, 39 Liriantha appendiculata, 291, 295 Liriope, 288, 290, 295; L. rosacea, 289 Lissodendoryx, 224 Lissomyxilla, 225 Lister, A., on Myxomycetes, 93 n. Lister, J. J., on Foraminifera—reproduction, 67 f.; dimorphism, 67; palaeontology, 70; classification, 58 f.; on Astrosclera, 194 n. Lithistida, 194, 212, 215 Lithobius forficatus, host of Coccidium schubergi, 99 Lithocercus, 78; L. annularis, 82 Lithoninae, 193 f. Lithostrotion, 394 Littoral Protozoa, 48 Lituaria, 364 Lituola, 59 Lituolidaceae, 59 Living beings, characters of, 16 f.; criterion of, 11 Lizzia, 265, 270 Lobata, 414, 416, 418 f. Lobophytum, 333, 347, 349 Lobopodia, 47 n. Locomotion, in Heliozoa, 73 Loeb, Jacques, on "chemical" fertilisation, 32 n.; on polarity in regeneration, 229 f. Loftusia, 59, 70, 283 Lohmann, on Silicoflagellates, 114 n. Loisel, 237, 238 Longitudinal band of cilia of Dipleurula, 604; of Tornaria, 616 Longitudinal fission of Eutreptia viridis, 124; of Flagellates, 109, 115; of Bodo saltans, 117 f.; of Craspedomonadidae, 122 Longitudinal flagellum and groove in Dinoflagellata, 130, 131 Longitudinal section, of a young Asteroid, 445; of a young Ophiuroid, 486; of a Holothuroid, 563; of Antedon, 584; of free-swimming larva of Antedon, 618 Lophocalyx philippensis, 229 Lophoctenia, 418 Lophohelia, 399; L. prolifera, 399 Lophomonas, 111, 123 Lophophore, 579 Lophophyllum, 406 f. Louse, host for sexual process, etc., of Haemosporidian, 102 n. Loxodes, 137, 144, 152 n. Loxophyllum, 137, 152 Lucernaria, 320, 321; L. campanulata, 321 Lucernariidae, 320 Ludwig, on the blood-system of Asteroidea, 449; on the axial sinus of Ophiuroidea, 487; on the classification of Holothuroidea, 570 Lühe, figures of Lankesteria, 95 Luidia, 467 f., 471, 477; fossil, 475; larva of L. ciliaris, 605 Luminosity or phosphorescence of sea, due to Cystoflagellata, 132, 134 f.; to Dinoflagellata, 132 Lunule, 548 Lychnorhiza, 325 Lychnorhizidae, 325 Lytocarpus (Plumulariidae, 279), 277

Maas, 168, 189 n., 228 n., 230, 231 n., 232 n., 233, 324 MacBride, E. W., on Echinodermata, 425 f. MacBride, Massee, on Myxomycetes, 93 n. MacCallum, on malarial parasites, 103 M'Dougall, on motile reaction of Protozoa, 19 n. M'Intosh, 370 n. MacMunn, 169 Macrocnemic, 405 Macrocneminae, 405 Macrogonidia of Volvox, 126, 127 Macro-, prefix misused to mean "large," usually replaced here by "mega," q.v. Madrepora, 368, 373, 387, 389, 395; M. forma cervicornis, 395; M. forma palmata, 395; M. forma prolifera, 395 Madreporaria, 369, 371, 384 f. Madrepores, 326 = Madreporaria, q.v. Madreporic vesicle (or right hydrocoel) of Asterias rubens, 448; of Ophiothrix fragilis, 490; of Echinus esculentus, 528; development in Dipleurula, 609 Madreporidae, 395 Madreporite, 428; of Asterias rubens, 434; of Ophiothrix fragilis, 487; of Ophiuroidea, 493; of Cladophiurae, 493; of Echinus esculentus, 512, 517; of Echinocardium cordatum, 562; of Holothuria tubulosa, 564; of Elasipoda, 571; of Pelagothuriida, 572; in older fossil Pelmatozoa, 583; in Thecocystis sacculus, 596 Magosphaera, 89 Maidenhair tree, spermatozoa of, 38 Malacogorgia, 334, 357 Malarial fever produced by Acystosporidae, 103 f. Mal de Caderas (= falling sickness of cattle), 119 Male gamete, 33; motile in Lower Plants, Higher Cryptogams, Cycads, and Ginkgo, 38; of Pandorina, 128 f.; of Eudorina, 129; of Peritrichaceae, 151 —see also Sperm, Spermatozoon Malignant tumour, associated with Leydenia, 91 Mammals, syngamy in, 34; contain Sarcosporidiaceae in muscles, 108 Man, host of Amoeba, 57; of Coccidiaceae, 102 f.; of Sarcocystis tenella, 108 n.; of Trichomonas vaginalis, 119; of Trypanosomes, 119 f.; of the Ciliata Nyctotherus and Balantidium, 152 Manicina (Fam. Astraeidae, 399), 373; M. areolata, 370, 389 Mann, on function of nucleus, 24 n. Manson, on relation of Filarial disease to gnats or mosquitos, 103 Manson, the subject of inoculation experiments with malarial parasites, 106 Manubrium, 251 Margelis ramosa, 269 Margelopsis, 270, 274 f. Marginal, anchors, 320; cirrhi, 139 f. Marginaster, 464 Marine, Foraminifera, 60 f.; Heliozoa, 75 Marrow, red, of bones, habitat of resting states of malarial parasites, 106 n. Marshall, on amphidiscs, 179 Marshall, on Pennatulacea, 359 n.; on the physiology of the nervous system of Antedon rosacea, 585 Marsigli, 167 Marsupifer valdiviae, 379 Marsupites, 588 Maryna, 137; M. socialis, tube, 152 Massee, on Myxomycetes, 93 n. Mastigamoeba, 109, 112 Mastigophora (Bütschli's name for Flagellata), 109 Mastigophrys, 71, 75 n. Maturation of schizont of Acystosporidian parasite in relation to fever-fit, 103 Maupas, on Protozoa, 45; on life-cycle of Ciliata, 147 f. Maupasia, 111, 124 Mayer, 312 Meandrina, 388, 401; M. labyrinthica, 370 Mechanical stimuli, 19 f. Median dorsal process of ciliated band of Bipinnaria, 606 Medium gametes in Pandorina, 128 f. Medusa, 250; of Millepora, 259 f.; of Gymnoblastea, 262 f.; of Calyptoblastea, 277 f.; in Trachomedusae, 288 f.; in Narcomedusae, 295 f.; fresh-water, 292 f.; of Siphonophora, 302, 309; in Scyphozoa, 310 f. Medusome, 250, 251, 252 Megagamete, 33; see also Female gamete, Oosphere Megalactis griffithsi, 384 Megalosphere, megalospheric, 67 f. Megamastictora, 183, 184 f. Meganucleus, 136, 139 f., 144, 149 f.; degeneration of, in conjugation, 148 f.; new formation of, in conjugation, 148, 151; of Stylonychia mytilus, 139 f.; of Carchesium, 146; of Paramecium caudatum, 148, 151; of Trachelius ovum, 153; of Stentor, 154; of S. polymorphus, 156; of Suctoria, 160 f., 162; conjugation of, in Dendrocometes, 161 Megazooid of Vorticella, 157 Megazoospores, 85 Meissner, on classification of Spatangoidea, 554 n. Melanin, 103 Melitodes, 333, 351, 353; M. chamaeleon, 338; M. dichotoma, 338, 351 Melitodidae, 337, 351 Mellita, 548, 549 Melobesia, 422 Melonitidae, 557 Membrana reticularis, 199, 200 Membrane, undulating, of Flagellata, 110, 115, 123; of Trypanosoma, 115; of Trichonymphidae, 123; of Ciliata, 137, 139 f., 145, 156 f.; of Stylonychia mytilus, 139; of Pleuronema, 145; of P. chrysalis, 153, 154; of Caenomorpha uniserialis, 155; of Vorticella, 156, 157 Membranella, 137, 139 f., 145; of Stylonychia mytilus, 139 f.; of Metopus sigmoides, 154; of Caenomorpha uniserialis, 155; of Vorticella, 156 Meresjkowsky, 238, 274 Merozoite, 97; of Coccidium schubergi, 99 f., 101; of Haemosporidae, 102; of Acystosporidae, 103, 104 f. Mertensia, 417; M. ovum, 417; stage of Lobata and Cestoidea, 414 Mertensiidae, 417 Mesenchyme, 604 Mesenteric filaments, Alcyonaria, 331, 333; Zoantharia, 369 Mesenteries, of Alcyonaria, 329, 334; of Zoantharia, 329, 366 f., 368; of Asterias rubens, 439; of Holothuria nigra, 562; of Antedon rosacea, 585, 586 Mesnil, on Sporozoa, 94; Caullery and, on Actinomyxidiaceae, 98 n. Mesodinium, 137, 152 Mesogloea, 246; of Alcyonaria, 330 Metabolic, metabolism, 13 Metacnemes, 367 Metacrinus, 588, 591 Metallogorgia, 355 Metamorphosis, of Insects, 44; of Dipleurula, 610 f. Metamp, 168, 169 Metaphytes, 41 —see also Plants, Higher Metazoa, 40 f.; rheotaxy of, 21; origin of, from Protozoa, 40 f.; flagellate sperms of, 109; hosts of Polymastigidae, 111 —see also Animals, Higher Method of study of the life-cycle, of organisms of putrefaction, etc., 44; of Flagellata, 116; of Ciliata, 147 Metopus, 137; M. pyriformis, 154; M. sigmoides, 154 Metridium, 381 (= Actinoloba, q.v.) Metschnikoff, 167, 178, 237 n., 296 Microbes, 44 Microciona, 225 Microgamete, 33; of certain Coccidiaceae, 101 —see also Sperm, Spermatozoon Microgromia socialis, 59 f., 60 Microhydra, 256 Micromastictora, 183, 195 f. Micronuclei, micronucleus, 136, 139, 144 f., 148 f., 151 f., 155, 157, 159, 160 f.; of certain Flagellata, a blepharoplast, 109 n.; relations of Trypanosomic blepharoplast to, 121; of Stylonychia mytilus, 139; of Paramecium caudatum, 148, 151; in conjugation, 148 f.; numerous, of Stentor, 154; of Vorticella, 157; of Suctoria, 160 f.; of Podophrya, 160; of Acineta jolyi, 160 Micropyle, 230 Microscleres, 176 Microsolena, 404 Microsphere, microspheric, 67 f. Microzooid of Vorticella, 157 Microzoospores, 85 Miescher's tubes, 108 Migratory pairing nucleus, 149 f.; of Peritrichaceae, 151 f. Miliola (Quinqueloculina), 65 Miliolidaceae, 59 Miliolina, 59, 66, 70 Milleporina, 257 f., 258, 260, 282; nematocysts of, 247, 259 Milleporina, 257 Mimicry among Gymnostomaceous Ciliata, 152 n. Minchin, on Sporozoa, 94 f.; on Sponges, 168, 172 n., 185, 186 n., 227 n., 232, 316 n. Minnows prey on Anopheles, 106 Minous inermis, 268 Minyadidae, 328, 366, 377, 383 Miserly cells, 32 f. Mithrodia, 464 Mithrodiidae, 464 Mitosis, 25, 26, 27 f.; functions of, 28 f.; of micronuclei in Ciliata, 144 Mitrophanow, on trichocysts, 142 n. Mitrophyes, 306 Miyajima, 273 Mnemia, 420 Mnemiidae, 420 Mnemiopsis, 420 Mnestra (position undetermined), 269 Mohl, von, on protoplasm, 3 Mole-cricket, host of Lophomonas, 123 Molluscs, hosts of Gregarines, 98 Molluscum contagiosum, 102 Molpadiida, 568, 569, 575, 576, 577, 578 Monacanthid, 457 Monadidae, 111 Monadineae, applied to Proteomyxa by Cienkowsky and Zopf, 89 Monads, a name for the lowest, simplest Flagellata, 109, 116 n. Monas, 111, 119; M. dallingeri, gametes of, 116 n. Monaxon, 183, 184, 232 Monaxonic (= symmetrical about one single axis), 76 Monaxonida, 211, 216 f. Moniliform meganucleus of Stentor, 156 Monobrachiidae, 274 Monobrachium, 274 Monocaulus, 263, 273; M. imperator, 269, 273 Monocyclica, 594 Monocystis, 97 f. Monograptus, 282 Monophyes, 303, 306 Monophyidae, 306 Monoprionidae, 282 Monopylaea (= Nassellaria), 76 Monorhaphis, 197 Monosiga, 111, 122 Monosiphonic, 275 Monotrypasta (= Osculosa), 76 Monoxenia darwinii, 342 Monstrous Foraminiferal shells, possible formation of, 69 Montipora, 390, 396 Moore, 293 Mopsea, 353 Morgan, on regeneration, 35 n. Morphological contrast of Animals and Plants, 38 f. Mortensen, on classificatory value of pedicellariae, 532; on classification of Cidaridae, 534; of Echinothuriidae, 536 Moseley, 258, 333, 338, 345, 411 Mosquito (= gnat), 103 f.; dappled-wing-, intermediate hosts of Acystosporidae, 103 Mosquito-netting, a prophylactic against malarial fever, 103 Moss-dwelling Protozoa, 48 Mosser, F., 418 n. Motile organs, 17 f. Motile reactions of Protozoa, 19 f. Motility, 9 Motion, ciliary, 18; gliding, of protoplasm, 47 n. Moulting of cuticle or cell-wall in Dinoflagellata, 130; of Dendrocometes, 161 Mouth, of Flagellata, 113; absent from Opalinidae, 123; of Maupasia, 124; excreta expelled by, in Noctiluca, 133; of Ciliata, 137, 145 f.; of Gymnostomaceae, 137, 143, 145, 152; of Stylonychia mytilus, 139 f.; of Dysteria, 145; of Pleuronema, 145; of P. chrysalis, 153; of Paramecium caudatum, 148, 151; trichocysts of, in Gymnostomaceae, 143; of Trachelius ovum, 153 Mouth-angle of Ophiothrix fragilis, 482 Mouth-frame, of Asteroidea, 436, 483; of Ophiothrix fragilis, 482; of Ophiuroidea, 483, 492 f.; of Ophiarachna incrassata, 484; of Ophiacantha, 492; of Ophioscolex, 492; of Ophiothrix, 492 Mouth-papilla, of Ophiuroidea, 483, 492; of Ophiocoma, 493 Movements, amoeboid, 5 f., 125 n.; of Protista, 16 f.; of Higher Plants, how produced, 38; springing, of Bodo saltans, 114; of Euglena, 124 f.; euglenoid, 125 f.; metabolic, 125 n.; of Sporozoa, 125 n.; of Stylonychia, 138; springing, of tailed Ciliata, 141 n.; of Halteria, 155; of Suctorian tentacles, 159 f. Muggiaea, 306; M. atlantica, 304; M. kochii, 303 Müller, J., on recognition of Echinoid larva, 518; on the name Pluteus, 607 Müller, O. F., on Protozoa, 45 Multicilia, 109 Multinucleate Amoeba (Pelomyxa), 16; Protozoa, regeneration of, 35 Multiple budding, in Suctoria, 160 f. Multiple fission, 30 f. —see also Brood-division Murbach, 248 n., 288 Muricea, 356 Muriceidae, 330, 355 Muscle of Vorticella, 157 Muscle-cell, 19 Muscular contraction, physical explanation of, 19 —see also Myonemes Mussa, 401 Mycetozoa (= Myxomycetes, q.v.), 50, 90 f.; in relation to Fungi, 40; studied by botanists, 45; relations of, 49 Myocyte, 96, 98 Myonemes, 19, 96; of Trypanosoma, 120 f. of Stylonychia, 140; of Ciliata, 142; of Vorticella, 157 Myophrisks, 80 Myriophrys, 71 Myriothela, 269, 274 Myriothelidae, 274 Myxaster, 466 Myxasteridae, 464 Myxastrum, 70, 73 Myxidium, 98; M. lieberkühnii, 107 Myxilla, 225 Myxobolus, 98; spores of, 107 Myxobrachia, 83 Myxogasteres, Myxogastres, 90 f. Myxoidea, 89 Myxomycetes, 90 f.; rheotaxy of plasmodium in, 21 —see also Mycetozoa Myxospongiae, 196 Myxosporidiaceae, 98, 106 f.; spores, 107

Nagana disease of hoofed quadrupeds, 119 Naked Protozoa, 51 n. Narcomedusae, 288, 295 f. Nardoa, 455, 456, 471 Nassellaria, 76, 78; skeleton of, 83; geological occurrence of, 88 Nassoidea, 78 Nausithoe, 322; Scyphistoma of (= Spongicola fistularis), 317; N. punctate, 322; N. rubra, 322 Nectocalyces, 297, 298, 305 Needham on spontaneous generation, 43 Nematocyst, 246 f., 247; of Actinomyxidiaceae, 98; of Myxosporidiaceae, 98, 107; of Myxobolus mülleri, 107; of Polykrikos, 131, 249; of Epistylis, 249; of Aeolis, 248; of Hydra, 247; of Millepora, 247, 259; of Siphonophora, 300; of Scyphozoa, 312; of Alcyonium, 247; of Sarcophytum, 248; of Cerianthus, 247 Nematodes parasitic in blood, 103 Nematophores, 277 Nemocera (= gnats or mosquitos), 103 n. Neohelia, 399 Neolampas, 554 Neosporidia, 97, 106 Nephthya, 341, 349 Nephthyidae, 349 Neresheimer, on neurophane fibrils in Ciliata, 143 n. Nerve-ring, of Asterias rubens, 444, 447; of Ophiothrix fragilis, 488; of Echinus esculentus, 518, 521, 527; of Antedon rosacea, 583; outer, of A. rosacea, 585 Nervous fibrils in Ciliata, 143 Nervous system, in Animals, not in Plants, 39 f.; of Asterias rubens, 444 f.; of Ophiothrix fragilis, 488; of Echinus esculentus, 518 f.; of Holothuria nigra, 566; of Antedon rosacea, 583 f. Neuron, 444 Neurophane (= supposed nervous fibrils in Ciliata), 143 n. Newts, Trichodina parasitic in, 158 Nitriles in relation to nutrition, 36 Noctiluca, 110, 132 f.; endosarc, 144; N. miliaris, 133 Nodosaria, 59, 63, 66 f. Nosema, 98; N. bombycis, 107; organism of pébrine, 107 Nubecularia, 59 Nuclear apparatus, of Infusoria, 48, 136; of Ciliata, 139 f., 144 f.; of diffused granules, in marine Ciliata, 144 n.; of Suctoria, 159 —bipartition in Trichosphaerium, 54 —reduction of Actinosphaerium, 75 n.; of Monocystis, 96; of Coccidiaceae, 100, 104 f.; of Acystosporidae, 104 f.; of Myxosporidiaceae, 107; of Flagellates, 116 n. —divisions, in spores of Lankesteria, 95 —see also Mitosis, Karyokinesis Nuclearia, 70 Nuclein mass (= karyosome), 24 Nucleinic acid, 7 n. Nucleole, nucleolus, 7, 24, 25 f., 27; of Sea-urchin ovum, 7; of Sphaerella, 126 Nucleolidae, 554 Nudeolites, 554 Nucleoplasm, 6 Nucleoproteids, 12 Nucleus, 6; of cell, 6 f.; of Amoeba, 5 f.; of A. polypodia, 10; resting, function of, 24 n —in mitosis, 25 f., 27 f.; —of Euglypha, 29; of Paramecium caudatum, 148 —pairing state of, 34; of Ciliata, 150 f.; of Paramecium caudatum, 148 —of Rhizopods, 52; of Pelomyxa, 52; of Microgromia socialis, 60; of Foraminifera, 62; of mega- and microspheric forms of Foraminifera, 68 f.; of Heliozoa, 71, 72, 74; of Clathrulina, 74; of Radiolaria, 76; of Collozoum inerme, 76; of Myxomycetes, 92; of Sporozoa, 95 f.; of Gregarines, 95 f., 98 f.; of Bodo saltans, 117; kineto-, of Trypanosoma noctuae, 120, 121; trophic, of T. noctuae, 120; of Choanoflagellates, 122; of Opalina, 123; of Maupasia, 124; of Sphaerella, 126; of Volvox, 126; of Noctiluca, 133 —fusion- or zygote-, 150; of Paramecium caudatum, 148 —see also Meganucleus, Micronucleus, Gametonuclei, Nuclear apparatus Nuda, 423 Nummulitaceae, 59 Nummulites, 59, 63, 70 Nussbaum, on regeneration in Protozoa, 35 n.; on Hydra, 254 Nutrition, 9; animal and vegetal, 35 f.; of Flagellates, 110 f., 113; of Dinoflagellates, 130 f.—see Holozoic, Holophytic, Saprophytic —of Alcyonaria, 339 Nutritive function of granular cytoplasm of muscle-cell, 19 Nuttall, history of discoveries on Acystosporidae, 103 Nutting, 276, 280 n. Nyctotherus, 137; habitat of, 152

Obelia, 280 Oceanapia, 223 Ocellus, 252 Octactine, 200 Octactinellida, 208 Octotremacis, 346 Ocular plate of Echinus esculentus, 512 Oculina, 399 Oculinidae, 399 Ocyroe, 420; O. crystallina, 419 Ocyroidae, 420 Odinia, 474, 475 Oecology of Protista, 43 Oesophagus, of Asterias rubens, 438; of Echinus esculentus, 516; of Holothuria nigra, 562; of Antedon rosacea, 583; of Dipleurula, 605 Ogilvie, M., 401 n. Oikomonadidae, 111 Oikomonas, 111, 112 Oil-drops, of Radiolaria, 79 f.; luminous, 80 Oil-globules, 37; of Ciliata, 144 Oleocyst, 305 Oligotrichaceae, 137, 155 Olindias, 291; O. mülleri, 291 Olindiidae, 289, 291 Olindioides, 291; O. formosa, 291 Olynthus, 185 Omne vivum, ex ovo, 42; ex vivo, 44 Onychaster, 203 Onychaster, 502 Oocyte (a cell which by unequal divisions or mere nuclear divisions becomes converted into an oosphere), 100 Oogamete of Coccidiaceae, 100 f. Ookinete (active zygote) or oosperm, of Acystosporidae, 104 f.; of Trypanosoma noctuae, 120 Oolitic limestones, nucleus of concretions of, 70 Oosperm, 34; of Sporozoa, 96 f.; of Volvox globator, 127 f. Oosphere, 31; formation of, in Metazoa, 75 n.; of Gregarinidaceae, 99, 100; of Coccidiaceae, 100 f.; of Acystosporidae, 104 f. Oospore (= zygotospore), from bisexual syngamy, 100; of Volvox globator, 127 f. Ooze, Globigerina, 61; Radiolarian, 87 Oozooid, 358 Opalina, 111; galvanotaxy, 22; ciliiform flagella, 114; species, 124 n.; nuclei, 144 n.; systematic position of, 144 n., 145 n.; O. ranarum, 123 Opalinidae, 111, 123 f. Opalinopsidae, 145 n. Opercularia, 138, 158 Operculum of central capsule of Phaeodaria, 76, 82 Ophiacantha, 492, 499; mouth-frame, 492; O. chelys, 499 Ophiactis, 498; O. balli, 498; O. virens, 491, 498 Ophiarachna, 481, 499 Ophicephalous pedicellariae, of Echinus esculentus, 508; of E. acutus, 509; of E. elegans, 510; absent in Cidaridae, 534; of Echinarachnius parma, 544 Ophidiaster, 471 Ophiocoma, 493, 499; O. nigra, 499 Ophiocomidae, 499 Ophiodermatidae, 495 n. Ophiodes, 277, 280 Ophiogeron, 494 Ophioglypha—see Ophiura Ophiohelus, 481, 491, 494; O. umbella, skeleton, 493 Ophiolepididae, 495 Ophiomusium, 497; O. pulchellum, 497, 498 Ophiomyxa, 493, 494; O. pentagona, 494 Ophiopholis, 491, 499; O. aculeata, 499 Ophiopluteus, 606, 608; metamorphosis of, 613 Ophiopsila, 499 Ophiopteron, 492, 500 Ophiopyrgus, 493, 497 Ophioscolex, mouth-frame, 492 Ophioteresis, 481, 491, 494 Ophiothrix, 493, 499; mouth-frame, 492; O. fragilis (pentaphyllum), 478, 479; arm of, 479; vertebra, 480, 491; podia, 479; mouth-frame, 482; disc, 484; genital bursa and respiratory movements, 485; alimentary canal, 485; water-vascular system, 486; axial sinus, 487; perihaemal spaces, 488; nervous system, 488; genital organs, 489 Ophiura (Ophioglypha), 496; O. albida, 497; O. bullata, 495, 496; O. ciliaris, 485 n., 497 Ophiuroidea (Brittle Stars), 431, 477 f., 561; mesenchyme of larva, 604; development of, 606, 606, 608, 613; phylogeny, 622 Ophlitaspongia, 225 Ophrydium, 138, 158 Ophryocystis, 97 Oplorhiza (Campanulariidae, 280), 277 Oractis, 377 Oral apparatus, of Ciliata, its atrophy and regeneration during conjugation, 151 Oral blood-ring, of Asterias rubens, 450; of Ophiothrix fragilis, 488; of Holothuria nigra, 567 Oral cleft or groove of Noctiluca, 132 f. Oral coelom of Antedon rosacea, 585 Oral plates, of Crinoidea, 588; of Thaumatocrinus, 589; of Hyocrinus, 588, 590; of Holopus, 588, 592; of Rhizocrinus, 589, 591; absent in adult Antedon, 589; of Rhizocrinidae, 590, 591; of Bathycrinus, 591; of Cystoidea, 598; of Blastoidea, 599; of young Antedon rosacea, 619 Oral spots of Protomastigaceae, 110 Oral valves, of Antedon rosacea, 581; of young A. rosacea, 619 Orbicella, 373, 375, 400 Orbiculina, 59, 66 Orbigny, A. d', on Foraminifera, 62 Orbitoides, 59 Orbitolites, 59, 66; pylomes, 64; dimorphism, 67; monstrous shell, 69 Orbulina, 59, 66; O. universa, 68 Orbulinella, habitat, 75 Organ-pipe Coral, 343 Organella, 44 n. Organic compounds, their function in nutrition, 35 f. Organoid, 44 n. Oriental sore, 121 Ornamentation of shell-wall in Foraminifera, 66 Oscarella, 196, 213, 225; A. lobularis, 230 Osculosa (Monotrypasta), 76 Osculum, of Radiolaria, 76; of Phaeodaria, 76, 82; of Sponges, 169, 171, 174, 188, 189 Ossicles of Holothuroidea, 569 Ostium, 169 Otocysts, of Elasipoda, 571; of Synaptida, 576 Outer perihaemal ring, of Asterias rubens, 448; development of, in Asterina gibbosa, 612; represented by lantern-coelom of Echinus esculentus, 524; by buccal sinus of Holothuria nigra, 566 Ovary of gnat infected by Trypanosoma germs, 120 Ovoid gland of Ophiothrix fragilis, 489 Ovum of Sea-urchin, 7; of Sarcocystis tenella, 108 n.; of Volvox globator, 127 f. —see also Oosphere, Oosperm, Egg Owl, blood parasites of, 120 Oxea, 183, 224 Oxyaster (an aster with a small centrum and oxeate actines), 222 Oxytricha, 138 Oxytylote (a rhabdus of which one actine is oxeate, the other tylote or knobbed, the latter directed towards the surface of the Sponge), 224

Pachychalina, 223 Pachymatisma, 215; P. johnstonia, 215, 222; P. normani, 215 Pairing in Trichosphaerium, 54 Pairing-cells, 31, 33 f.; in Lankesteria, 95 —see also Gametes, Syngamy Pairing nuclei, state of, 34; of Ciliata, 150; of Paramecium, 148 Palaeaster, 476 Palaeocoma, 476 Palaeodiscus, 557 Palaeoechinoidea, 556 Palaeoechinus, 557 Palephyra, 322 Pali, 370, 385, 387 Palmella state of Zooxanthella, 86 Palmipes, 461, 464; P. membranaceus, 464 Pamphagus, test of, 59 f. Panceri, 339 Pandorina morum, 111, 129 Pansporoblast of Myxosporidiaceae, 107 Pantostomata, 109 Papula (including dermal gill), 432, 457; compared to diplopore of Cystoidea, 599 Paractinopoda, 570 Paragaster, 187 Paragastric canals, 416 Paraglycogen (= paramylum), 95 Paragorgia, 333, 336, 351 Paralcyonium, 349 Paramecium, 137, 143 n., 151, 153; specific gravity of, 13 n.; thigmotaxy of, 20; reaction to repellent stimuli, 21 n.; thermotaxy of, 22; galvanotaxy of, 22; chemiotaxy of, 23; trichocysts of, 143, 151; contractile vacuoles of, 143 n., 151; P. bursaria, 153; P. caudatum, 151; in conjugation, 148 Paramoeba, 51 n., 110; nutrition of, 113; formation and regeneration of chromatophores in, 115; P. eilhardii, 116 n.; reproduction of, 116 n. Paramuricea, 356; spicule, 336 Paramylum (= paraglycogen), 37, 95, 115; in Gregarines, 95; in Flagellates, 115; in Ciliata, 144 Parangi, 121 n. Parapyle, 81 Pararchaster, 466 Parasites, in relation to brood-formation, 33; internal, belonging to Metazoa, nutrition of, 38; of man, 57, 103 f., 108 n., 119 f., 152; of Radiolaria, 86 f.; of Sticholonche, 86, 161; of plants, 88 f.; of Acantharia, 86, 161; of Crucifers, 89; of Crustacea, 89; of earthworm, 95; of centipedes, 99; of Epizoanthus glacialis, 99; of Lithobius forficatus, 99; of cold-blooded Vertebrates, 102; of rabbit, 102; of cattle, 102, 119 f.; of frog, 102, 124; of birds, 103; of fish, 107; of silkworm, 107; of fish, 107, 119, 152; of sheep, 108 n.; of insects, 111, 123; of Amphibia, 111, 123 f., 158; of dog, 119; of horse, 119; of ox, 119; of Rodents, 119; of owl, 120 f.; of cockroach, 123; of mole-cricket, 123; of Termites, 123; of Metazoa, 152; of Ruminants, 152; of Heliozoa, 155; of Raphidiophrys, 155; of Hydra, 158; of newts, 158; of Ciliata, 159 Parasitic, Proteomyxa, 48, 88 f.; Sporozoa, 48, 94 f.; Flagellata, 48, 111, 119 f., 123; Rhizopoda, 57; Ciliata, 152, 158; Suctoria, 161; Hydrozoa, 268 f. Parasmilia, 401 Parazoa, 181 Parazoanthus, 406; P. anguicomus, 406; P. separatus, 406; P. tunicans, 406 Parenchymalia, 201 Parenchymula, 227 Parisis, 351 Parker, 371 Parkeria, 283 Paroral cilia, 139; of Vorticella, 156 n. Parthenogenesis, of malarial parasites, conjectured, 106 n. Pasteur, on organisms of fermentation and putrefaction, 43; on nature of pébrine (Nosema bombycis), 107 Patellina, 59; reproduction of, 69 Patina, 580; of Antedon rosacea, 582; of Thaumatocrinus, 589; of Hyocrinus, 590; of Rhizocrinidae, 590; of Pentacrinidae, 591 Paulinella, 52; test of, 54; pylome of, 54 Pavonia (Fungiidae, 403), 390 Paxilla, 455; evolution of, 466; relation to granules of Valvata, 471 Paxillosa, 461, 466 f.; restriction of papulae to dorsal surface, 469 Peachia, 366, 380; P. hastata, 370 Pébrine, 107 Pectinate pedicellariae, 456, 466 Pectyllidae, 294 Pectyllis, 294 Pedal laceration, 372 Pedal nerve, of Asterias rubens, 455; of Ophiothrix fragilis, 488; of Echinus esculentus, 518; of Holothuria nigra, 566 Pedicellaria, of Asterias rubens, 432; of A. glacialis, 434; of Asteroidea, 456; alveolate, 456; pectinate, 456; pincer-shaped, 456; valvate, 456; forcipulate, 433, 434, 456, 462; representatives in Ophiuroidea, 492; in Ophiothrix fragilis, 492; in Ophiohelus, 492, 493; of Echinus acutus, 509; of E. esculentus, 506 f., 507; tridactyle, 506, 509, 510; gemmiform, 506, 509, 510; trifoliate, 508, 509, 510; ophicephalous, 508, 509, 510; function of, 508 f.; of Endocyclica, 532; of Cidaridae, 532; of Echinothuriidae, 532, 535; of Centrostephanus longispinosus, 532; of Echinarachnius parma, 544, 545; of Echinocardium cordatum, 550; absent in Pelmatozoa, 582 Pedicellaster, 474 Pedicellasteridae, 456, 474 Pegantha, 296 Peganthidae, 296 Pekelharing, 187 n., 234 n., 237 Pelagia, 311, 312, 315, 316, 323; P. noctiluca, 311; P. perla, 323; P. phosphora, 311, 323 Pelagic, Foraminifera, 61, 66, 69; Radiolaria, 76; Dinoflagellates, 131 Pelagiidae, 323 Pelagohydra, 263, 274; P. mirabilis, 274 Pelagohydridae, 274 Pelagothuria, 568, 569, 572; P. natans, 572 Pelagothuriida, 572, 577, 578 Pellicle, of Protozoa, 46; of Flagellates, 109 f., 113; of Noctiluca, 133; of Ciliata, 139, 141, 142; of Coleps, 141, 152; of Dysteria, 153; of Vorticella, 157; of Suctoria, 159; of tentacles of Suctoria, 161 —see also Cuticle Pelmatozoa, 430, 579 f.; phylogeny of, 621 Pelomyxa, 51; P. palustris, 52 f.; pepsin in, 16 Penard, on Heliozoa, 71; on Rhizopoda, 58 n. Peneroplis, 59, 66; pylomes of, 64 Peniagone, 572 Pennaria, 272 Pennariidae, 272 Pennatula, 361; P. grandis, 361; P. murrayi, 359, 362; P. naresi, 362; P. phosphorea, 338, 361 Pennatulacea, 333, 335, 337, 358, 358, 359, 363 f. Pentaceros, 472 Pentacerotidae, 457, 458, 459, 471 Pentachogon, 294 Pentacrinidae, 588, 589, 591 f. Pentacrinoidea, 595 Pentacrinus (Isocrinus), 591 f.; P. asteria, 592; P. maclearanus, 593 Pentagonaster, 471; P. japonicus, 472 Pentagonasteridae, 455, 471 Pentremites, 599 Pepsin, 16 Peptic, digestion, 16; juice in Carchesium, 147 Peptones, 15 Perforate, Corals, 371; Foraminifera, 58 f. Peribolaster, 453, 463 Peribranchial spaces of Asterias rubens, 449 Pericolpa, 322 Peridiniales, synonym of Dinoflagellata used by Schütt, 119, 132 Peridinium, 110; fossil, 132; P. divergens, 131 Perigonimus, 265, 266, 269 Perihaemal spaces (or canals), of Asterias rubens, 448; of Ophiothrix fragilis, 481, 488; of Echinus esculentus, 524; of Holothuria nigra, 566 Peripatus, segmentation of, 32 n. Periphylla, 311, 314, 322; P. regina, 322 Periphyllidae, 310, 322 Periproct, of Echinus esculentus, 504, 507, 512, 513, 534; of Endocyclica, 530, 534, 538; of Cidaridae, 530, 533, 534; of Arbaciidae, 530; of Echinothuriidae, 535; development of, in young Echinoid, 613 Peripylaea (= Spumellaria), 76 Perisarc, 251, 263 Perisiphonia, 277, 280 Peristalsis of intestine of Holothuria nigra, 563 Peristome, of Ciliata, 137 f.; in fission, 147; of Peritrichaceae, 155 f.; of Vorticellidae, 155 f., 157; of Asterias rubens, 434; of Echinus esculentus, 505, 513, 514; of Asteroidea, 514; of Cidaridae, 514, 530, 533; of Endocyclica, 530; of Echinothuriidae, 535; of Asthenosoma hystrix, 537; of Saleniidae, 537; of Arbaciidae, 538; of Diadematidae, 538; of Echinidae, 539; of Echinocardium cordatum, 550; of Spatangoidea, 553; of Palaeostomatidae, 554 Peristomial area, 139; of Caenomorpha and Metopus, 154; of Bursaria, 155 Peristomial collar, 142, 156, 157 Peristomial plate, of Ophiothrix fragilis, 483; of Endocyclica, 530; of Cidaridae, 530, 533; of Echinothuriidae, 530, 535; of Saleniidae, 537; of Arbaciidae, 538; of Echinus microtuberculatus, 540 Peritoneum, of Asterias rubens, 437; of Holothuria nigra, 567 Peritrichaceae, 138; pellicle, 141; myonemes, 142; trichocysts, 143; contractile vacuole and reservoir, 145; pharynx, vestibule, mode of feeding, 145; fission, 147; conjugation, 151; peristomial collar, 156, 157 Perkins, 232 n., 290 Peronella, 549 Peronium, 295 Perrier, on classification of Asteroidea, 461 Persian Tick, 121 Petal, of Echinarachnius parma, 545; of Fibularidae, 549; of Echinanthidae, 549; of Echinocardium cordatum, 551 Petalocrinus, 595 Petasidae, 294 Petasus, 294 Peters, 414 n. Petrostroma, 193; P. schulzei, 193 Pfeiffer, on Sporozoa, 94 Phacella, 314 Phacotus, 111; shell, 113 Phaeoconchia, 79, 85 Phaeocystina, 79, 82, 87 Phaeodaria (Cannopylaea, Tripylaea), 76, 79; skeleton, 82, 84, 85; central capsule, 82, 84; fission, 85 Phaeodium, 76, 81, 82 Phaeogromia, 79 Phaeosphaeria, 79 Phakellia, 224 Phalangopora, 284, 286 Phalansteridae, 111 Phalansterium, 113 Phanerocodonic, 253, 265 Phanerozonate, 454 Pharetronidae, 192 Pharyngella, 79, 85 Pharynx, of Stylonychia mytilus, 139; of Ciliata, 145; of Gymnostomaceae, 145; of Paramecium caudatum, 151; of Caenomorpha uniserialis, 155; of Peritrichaceae, 145; of Carchesium polypinum, 146 f.; of Vorticella, 156, 157 Pharynx-tube of Euglenaceae, 124 f. —see also Flagellar Pit Pheronema, 204; P. carpenteri, 204, 205, 221 Phialidium temporarium, 281 Pholidaster, 474 Phoriospongia, 220 Phosphorescence, of Dinoflagellata, 132; of Cystoflagellata, 132, 134; of Noctiluca, 132, 134; of Scyphozoa, 311; of Alcyonaria, 338; of Pennatulids, 361; of Ctenophores, 414 Phosphorescent oil-drops in Radiolaria, 80 Photopathy, 21 Phototaxy, 21; of Euglena, 125 Phycochromaceae, 39 Phycomycetes Zoosporeae related to Flagellata, 109 Phycomycetous Fungi, relations of, 48 Phylactocarp, 276 Phyllactidae, 382 Phyllangia, 400; P. americana, 374 Phyllode, 553 Phyllograptus, 282 Phyllophorus, 573; P. rugosus, 567; P. urna, 574 Physalia, 300, 302, 304, 308 Physiological contrast of Animals and Plants, 38 Physiology, of cell and protoplasm, 3 f.; of Sponges, 234 f.; of nervous system of Echinoidea, 519 f. Physonectidae, 301, 307 Physophora, 301, 308; P. borealis, 304 Physophorae, 307 Physophorinae, 308 Pigment, of Stentor, 154; of Sponges, 169, 238; -granules, of Phaeodaria, 76, 80 f. Pinacocyte, 170, 213, 237 Pincer-shaped pedicellariae, 456 Pineau, on spontaneous generation, 43 Pinnule, of Antedon rosacea, 581, 583; of A. eschrichtii, 594; of Hyocrinus, 590; of Metacrinus, 592; of fossil Crinoidea, 595 Pinulus (a pentactine triaxon in which the unpaired actine bears lateral spines and projects beyond the bounding surface), 204 Piroplasma, 120 f. Placosmilia, 401 Placospongia, spicules of, 233 Plakina, 212, 213; P. monolopha, 210, 212, 213 Plankton, Protozoa of, 48; Foraminifera of, 61; Radiolaria of, 75 Planorbulina, 59, 63 Plant(s), definition, 39; Animals and, discussion on, 35 f.; Higher, movements of, 38; insectivorous, 38; -Protists, relations of, 48; -cells, wall of, 37; protoplasmic connexions of, 37 —see also Metaphytes Planula, 341 Plasmodiophora, 89 Plasmodium, 30; rheotaxy, 21; of Myxomycetes, 50, 90 f.; of Proteomyxa, 88; of Didymium, 92 Plasmodium, a generic name given to Acystosporid Coccidiaceae producing malarial fever, 103 f.—see Haemamoeba, Laverania Plastid, 21, 36 f.; of Paulinella, 54 n.; of Flagellates, 110, 112 f.; of Trachelomonas, 112 —see also Chromoplasts, Chromatophore, Chromoplastid Plastogamy, 30, 34 n.; of Rhizopods, 56; of Foraminifera, Discorbina and Patellina, 69; temporary, in Actinophrys sol, 72; of Myxomycetes, 90 f. Plastron, of Echinocardium cordatum, 550; of Sternata, 554 Plate, on Dendrocometes, 162 Plates, siliceous, of shell of Rhizopods, 29, 53 f.; ctenophoral, 141, 412 f. Platt, Julia B., on density of living protoplasm, 13 n. Platybrissus, 554 Platyctenea, 413, 416, 421 Platyhelminthes, bladder of, 14 n. Plectinia, 193 Plectoidea, 78 Plectroninia, 193, 193; P. halli, 193 Plesiofungiidae, 403 Plesioporitidae, 404 Pleurobrachia, 418; P. pileus, 416, 417, 418; P. rhodopis, 418 Pleurobrachiidae, 418 Pleurocorallium, 352 Pleurocoralloides, 352 Pleurogorgia, 355 Pleuronema, 137; P. chrysalis, 153, 154 Plexaura, 356 Plexauridae, 356 Plimmer and Rose Bradford, on Trypanosoma, 121 Pliobothrus, 284, 286 Plocamia, 223 Plumohalichondria, 225 Plumularia, 279; P. echinulata, 276; P. halecioides, 276; P. profunda, 275; P. setacea, 276 Pluteus, 607 Pneumatophore, 300 f., 307 f. Pneumatopyles, 309 Pneumotaxy, 23 Pocillon, 223 Pocillopora, 375, 402, 402; P. septata, 402 Pocilloporidae, 401 Podium, 428; of Ophiothrix fragilis, 479 f., 487; of Holothuria nigra, 561; of Elasipoda, 571 f.; of Molpadiida, 575; of Antedon rosacea, 582 Podocoryne, 270 Podocorynidae, 270 Podoplast, 19 n. —see also Blepharoplast Podostoma, 52; transition between pseudopodium and flagellum in, 47 n. Poecillastra compressa, 213, 222 Polar body, in Heliozoan syngamy, 72, 74 Polar fields, 415 Polian vesicle, of Asteroidea, 458; of Ctenodiscus, 458; of Solasteridae, 463; of Ophiothrix fragilis, 487; of Echinus esculentus, 525; of Holothuria nigra, 566 Polyaxon, 184 Polycanna, 278 Polycystineae (= Radiolarian skeletons), 87 Polycyttaria (= colonial Radiolaria), 76, 84 f. Polygastrica (Ehrenberg's name for Ciliata), 146 Polykrikos, 110, 113 n., 131 f. Polymastia, 224 Polymastigidae, 111 Polymitus form of male gametogonium of Acystosporidae liberating sperms, 104 f. Polymorphina, 59 Polyoeca, 111; stalk of, 113 Polyorchis, 278 Polyphyes, 307 Polyphyidae, 307 Polypodium, 257 Polyps, 245, 246; alternation of generations in, 44, 250 Polysiphonic, 276 Polystomella, 59; dimorphism and life-history of, 67 f. Polythalamia (= Foraminifera with more than one chamber to shell), 64 Polytoma, 111; brood-division of active, 115; P. uvella, gametes of, 116 n. Polytomeae, Francé on, 119 n. Polytrema, 59; shell substance of, 62 Polytremacis, 346 Polyzoa, 428, 579; Entoprocta, 621 Pontosphaera, 110 Porania, 455, 464; P. pulvillus, 464 Poraniidae, 464 Porcellanaster, 471; P. pacificus, 459; P. caeruleus, 470 Porcellanasteridae, 455, 459, 470 Porcellanous Foraminifera, 58, 59, 62 Pore(s), in test of Foraminifera, 64; in central capsule of Radiolaria, 76; of contractile vacuole, 14; of Ciliata, 143; of Trachelius ovum, 153; of embryonic cavity of Suctoria, not seen in Choanophrya, 161 n.; of Sponges, 186, 187, 188, 189, 198 Pore-canal, of Asterias rubens, 441; of Ophiothrix fragilis, 486, 487; of Echinus esculentus, 517; of Echinocardium cordatum, 552; of a larval Holothuroid, 564; of Elasipoda, 571; of Antedon rosacea, 583; of its larva, 619; of Dipleurula, 608; of larva of Asterina gibbosa, 612; of Balanoglossus, 617 Pore-plate, of Echinus esculentus, 512; of Strongylocentrotus droëbachiensis, 512; of Endocyclica, 530 f.; of petals of Echinarachnius parma, 544 Pore-rhomb, 597, 598 Porifera, 163 f.; definition, 180; systematic position, 181 —see also Sponges Porites, 368 f., 373, 387, 388, 397 Poritidae, 396 Porocone, 81 Porocyte, 186, 199, 231 Porosphaera, 193, 282 Porpita, 309 Porta, on reproduction of Radiolaria Acantharia, 86 n. Porulosa (Holotrypasta), 76 f. Portuguese Man-of-War, 300, 308 Post-abdomen = fourth chamber of Monaxonic Radiolarian shell, 84 Posterior dorsal process, of ciliated band, of Bipinnaria and Ophiopluteus, 606; of Echinopluteus, 607; of Auricularia, 608 Posterior lateral process, of ciliated band, of Bipinnaria, Ophiopluteus, and Ophiothrix fragilis, 606; of Echinopluteus, 607 Posterior wreath, of Peritrichaceae, 138; of Vorticella, 156, 157; of Trichodina, 158 Post-oral process, of ciliated band, of Bipinnaria and Ophiopluteus, 606; of Echinopluteus, 607 Potato, rest and germination of, 32 Poteriodendron, 111 Potts, 180 Pouchet (the elder), on spontaneous generation, 43 Pouchet, Georges, on Protozoa, 45 Pouchetia, 110 Pourtalesia, 554; P. jeffreysi, 554 Pourtalesiidae, 554 n. Prae-oral process, of ciliated band, of Bipinnaria and Ophiopluteus, 606; of Echinopluteus, 607 —see also Pre-oral Pratt, E. M., 339, 348 n., 399 n. Praya, 300, 306. Prayinae, 306 Pre-Cambrian Echinodermata, 623 Precious Corals, 326, 352 Pre-oral, cilia, 139; ridge, 139; undulating membrane, 139 —see also Prae-oral Preyer, on the response of Asteroidea to stimuli, 446 f.; on the intelligence of Ophiuroidea, 488 f. Primary spine, of Echinus esculentus, 506; of Cidaridae, 532; of Arbaciidae, 532; of Echinothuriidae, 532, 535; of Colobocentrotus, 532; of Heterocentrotus, 532; of Echinocardium cordatum, 550 Primnoa, 354; P. lepadifera, 338 Primnoidae, 330, 335, 354 Pringsheim, on exogamy in Pandorina, 34 n. Prionastraea (Astraeidae, 399), 375 Proboscis, of central capsule of Phaeodaria, 76 Progamic brood-division (= a brood-division to produce gametes), 96, 100 Proheliolites, 346 Promachocrinus, 594 Proper wall of Perforate Foraminiferal shell, 59, 63, 66 Prophylaxis, against mosquitos and malarial fever, 103, 106; against pébrine in silkworms, 107 Prosodus, 210 Prosopyle, 170 Prostalia, 201 Protanthea, 377 Protantheidae, 377 Protaspidochirota, 578 Protechinoidea, 623 Proteid(s), 12; digestion of, 15; formation of, 36; crystals, 37; reserves in Flagellates, 110; granules or spherules of Ciliata, 144; of Suctoria, 161 Proteleia, 218 Proteomyxa, 48 f., 50, 88, 89 f.; relations of, 40; studied by botanists, 45; parasitic in plant-cells, 48; distinctions from Flagellates, 109 Proteoses, 15 Proterospongia, 111, 113, 122, 181 f.; P. haeckeli, 182 Protista, 3 f.—see Protozoa Protoalcyonacea, 329, 342 Protoclypeastroidea, 548 Protocnemes, 367 Protocoelomata, 616, 617 Protodendrochirota, 578 Protoholothuroid, 577 Protoholothuroidea, 578 Protohydra, 256 Protomastigaceae, 110 f., 112; external plasmatic layer of, 113 Protomerite, of Gregarines, 97, 98 Protomyxa, 89 Protopelmatozoa, 623 Protophytes, 3 n. Protoplasm, 3 f.; structure of, 6; refractive index of, 6, 11 n.; movements of, 7; specific gravity of, 13 n.; of Protozoa, 46 f.; of Radiolaria, 79 f.; of Stylonychia, 140 Protospongia fenestrata, 207, 207 Prototheca, 385, 386 Protozoa, 1 f., 44 f.; characters, 40; parasitic, 40, 46; literature, 45 f.; geographical distribution, 47 f.; habitat, 47; classification, 50 Protractor muscles of Aristotle's lantern, 526 Protriaene (a triaene in which the cladi [branches] point forwards or in the opposite direction to the rhabdome or shaft), 224 Prouho, on transverse fission in Gonactinia, 371 n.; on gemmiform pedicellariae of Echinoidea, 509; on habits of Dorocidaris papillata, 535 Prunoidea, 77 Prunophracta, 78 Psammocora (Fungiidae, 403), 390 Pseudambulacrum, 599 Pseudaxonia, 350, 353 Pseudomonocyclic, 594 Pseudonavicella, 96 Pseudophellia arctica, 379 Pseudopodia (um), 4 f., 17, 47, 49, 50 f.; streaming of granules in, 17; Lang's classification of, 47 n.; transition to flagella, 47 n.; of Rhizopoda, 49, 50 f., 52; of Foraminifera, 49, 50, 60, 61, 65; of Microgromia, 59, 60; of Lieberkühnia, 61; of Allogromia, 65; of Miliola, 65; of Rotalia, 65; of Squamulina, 65; of Heliozoa, 49, 50, 71, 72 f.; of Radiolaria, 49, 50, 79, 80; of Lankesteria, 96 n.; of Flagellates, 109, 110; transitory, in Flagellates, 109; of Stentor, 152, 154; of young Gellius varius, 173, 174 Pseudopodiospores, 68 f. Pseudospora, 89; P. lindstedtii, 89 Psilaster, 470; P. acuminatus, 469 Psolus, 569, 573; P. ephippifer, 574, 575, 602 Psychropotes, 572 Pteraster, 455, 466; P. stellifer, 465; P. militaris, 466 Pterasteridae, 455, 466 Pterocephalus, 97 Pteroeides, 359, 361 Pteroeididae, 361 Puffballs, 91 Pulsatile vacuole, 14; = Contractile vacuole, q.v. Pulsellum, 18, 114 Punjab, dourine disease in, 119 Pupa, of Holothuroidea, 615 Pure cultures, 43 Putrefaction, organisms of, 42 f., 116 f. Pycnolithus, 346 Pycnopodia, 453, 474 Pygaster, 558, 559 Pygastrides, 548, 558; P. relictus, 548 Pylome, 53; of Rhizopods, 53 f.; double, in monstrous Rhizopods, 55; of Diaphorodon, 60; of Foraminifera, 64; of Radiolaria, 83; of Sphaeropylida, 77 n.; of Nassellaria, 83 Pyloric caeca (and duct), of Asterias rubens, 439; of Porcellanaster pacificus, 459; absent in Hyphalaster moseri, 459 Pyloric sac of Asterias rubens, 438 Pyramids, building-stone of, 70 Pyrenoid, 37, 115; of Sphaerella, 126 Pyrocystis, 110; P. fusiformis, 132 Pyrsonympha, 111; flagella of, 114 Pytheas, 223 Pythonaster, 464 Pythonasteridae, 464 Pyxicola, 138, 158