Letter XXXI…

Letter XXXI

STATES OF INSECTS.

PUPA STATE.

We have now traced our little animals through their egg and larva states, and have arrived at the third stage of their existence, the Pupa State. This, to include all, can only be defined,--that state intervening between the larva and imago, in which the parts and organs of the perfect insect, particularly those of sex, though in few cases fully developed, are prepared and fitted for their final and complete development in the last-mentioned state; and in which the majority of these animals are incapable of locomotion, or of taking food.

Pupæ, like larvæ, may be separated into two great divisions:--

I. Those which, in general form, more or less resemble the larvæ from which they have proceeded.

II. Those which are wholly unlike the larvæ from which they have proceeded.

I. To the first division belong, with some exceptions[562], the Dermaptera, Orthoptera, Hemiptera, and most Aptera, with the neuropterous tribes of Libellulina, Ephemerina, and the genus Termes, in the class Insecta; and the majority of the Arachnida. This, like the first division of larvæ, may be subdivided into two corresponding smaller sections; the first including those pupæ which resemble the larvæ, except in the relative proportion and number of some of their parts; and the second those that resemble them, except in having the rudiments of wings, or of wings and elytra.

i. The first subdivision will include the pupæ, if they may be so called[563], of insects of the Aptera order, and of the class Arachnida: as, lice, Poduræ, Lepismidæ, centipedes, millipedes, mites, harvest-men, spiders, scorpions, &c. These mostly differ from their larvæ only in that the relative length or number of their legs, the number of the segments of the body in some, or the development of their palpi, more nearly approach the characters of the perfect insect; and in that while in their larva state they have two or more skins to cast, previously to their assumption of the imago, in their pupa state they have but one. In fact, this last circumstance is the only one which, strictly speaking, characterizes the pupæ of this subdivision; as the changes which take place in the number and proportion of the organs are partly produced with each change of the larva's skin. And hence, as it is not easy to ascertain what number of skins a spider, for example, has yet to cast, and as both the larva and pupa differ so little from the perfect insect, it is very difficult to determine in what state insects of this division are. From this difficulty has probably arisen the too great multiplication of species in some of these tribes, particularly the Arachnida, the larva and pupa having been mistaken for perfect insects. The pupæ of this subdivision were named by Linné complete, from the near resemblance which they bear to the imago.

ii. The second subdivision will include the pupæ of the Dermaptera, Orthoptera and Hemiptera orders, with few exceptions; as likewise the Libellulina, Ephemerina, and Termitina? amongst the Neuroptera: including the well-known tribes of earwigs, cockroaches, crickets, grasshoppers, locusts, lanthorn-flies, froghoppers (Cicada L.), bugs, plant-lice, dragon-flies, day-flies, white ants, &c. Of these, as in the former subdivision, the pupæ are equally capable of eating and moving with the larvæ, which they resemble, except in having the rudiments of wings, or of wings and elytra. The pupæ of the three orders first enumerated differ from those of the Neuroptera in resembling the perfect insect in most instances, both as to shape and the organs for taking their food; and in all other respects, except in not having their wings and elytra fully developed[564]. The resemblance of the pupæ of the Libellulina and Ephemerina to the perfect insects is more distant, and the above organs in the two states are very dissimilar; for the pupæ of the former are furnished with a prehensory mask similar to that of the larvæ before described[565], which the perfect insect has not; and those of the latter with the usual oral organs of masticating insects, of which the imago has scarcely the rudiments.

I have applied the term rudiments to the wings and elytra in this state, not in a strict sense, but merely to denote their appearance; for in fact the wings, &c. are complete, but only folded up longitudinally and transversely, and inclosed in membranous cases, which when the last change takes place remain attached to the puparium or pupa-case. The tegmina or hemelytra in this state usually cover the wings, and the upper wings the under; but in the Libellulina both are usually visible. Though commonly very small compared with the instruments of flight in the perfect insect, some of these rudiments, contrasted with the majority, are of considerable magnitude. This is the case with those of some species of Chermes, as we learn from De Geer[566].

II. The second grand division comprises by far the largest number of pupæ: those of all coleopterous, strepsipterous, lepidopterous, hymenopterous, dipterous, and aphanipterous, and by far the majority of neuropterous insects, as well as the hemipterous genus Aleyrodes, and one sex of Coccus of the same order. These pupæ, however, though agreeing in the circumstance of being unlike the larvæ from which they proceed, differ from each other in several respects, and require to be divided into three great sections, as under:--

i. Those pupæ in which the parts of the future insect, being folded up under a membranous skin closely applying to each, are distinctly visible. To this head belong generally, the pupæ of coleopterous[567] and hymenopterous insects; those of the neuropterous genera Myrmeleon and Hemerobius, &c.; the Trichoptera; amongst the Diptera, Culex, Tipula L., Tabanus, Bombylius, &c.; and that of the flea (Pulex). These were the incomplete pupæ of Linné.

ii. Those pupæ in which the parts of the future insect, being folded up under a harder skin, are less distinctly discoverable. To this subdivision belong the pupæ of all Lepidoptera, and of them alone. These are what Linné termed obtected pupæ.

iii. Those pupæ which are inclosed in the thick and opaque skin of the larva, through which no trace of the perfect insect can be discovered. These, which Linné termed coarctate pupæ, include a large proportion of the dipterous genera; as Œstrus L., Musca L., Empis L., Conops L., &c. &c.[568]

I shall next advert, chiefly to the pupæ of the grand division last described, under the distinct heads of substance, figure, and parts; colour, age, sex, motions, and extrication of the perfect insect.

* * * * *

i. As to their substance--at first interiorly all pupæ consist of a milky fluid, in which the unformed members of the future perfect insect may be said to float, and in which they may be discerned, and separated with the point of a pin[569]. In proportion as these acquire consistency, and are more and more developed by the absorption of the surrounding fluid, they occupy its place, and fill up the cavity of the puparium. The rest of this fluid passes off by transpiration[570]. Reaumur is of opinion that it is from the epiploon, or corps graisseux, that this matter is prepared, which he regards as analogous to the white of an egg[571]. In coarctate pupæ the included animal, or the pulp that contains its germes (in which the limbs and body at first are not discernible), fills at this period the whole skin-cocoon; but in proportion as the above evaporation takes place, and the consolidation of the body and parts proceeds, it shrinks at each end, so that when near assuming the imago, a considerable cavity appears both at the head and tail of the cocoon[572]. At this period of its existence, from the quantity of fluid included in the puparium, the animal weighs usually considerably more than it does when become a perfect insect[573].

The exterior integument or skin of pupæ, which is usually lined with a very thin white pellicle, is of different consistence in different orders. In the Coleoptera and Hymenoptera it is, with a few exceptions, of a soft and membranous texture; in the Lepidoptera (especially those that are not defended by cocoons), and Diptera, it is more rigid and harder, being either coriaceous or corneous. Lepidopterous pupæ, however, are not excluded from the last skin of the larvæ with this hard covering. At the moment of this change the envelope is nearly as soft and membranous as in the order first mentioned. But they are besides covered with a viscous fluid, which appears to ooze out, chiefly from under the wings, and which very soon drying, forms the exterior hard shell[574]. At first the antennæ, wings, and legs, like those of Coleoptera and Hymenoptera, can be each separated from the body; and it is only after these parts have been glued together by the fluid just mentioned, which takes place in less than twenty-four hours[575], that they are immoveably attached to the body of the pupa, as we usually see them. In fact, the essential difference between incomplete and obtected pupæ seems to be, that in the former the limbs and body are only covered each with a single membranous integument, whereas in the latter they are besides glued together by a substance which forms an additional and harder envelope. It is not easy to explain the alteration that takes place in the texture of the skin of such dipterous pupæ as retain the skin of the larva. In the latter this is generally a transparent and very fine membrane: yet the very same integument becomes to the pupa an opaque and rigid case.

The surface of the skin of the greater number of pupæ is smooth, but in those of many Papilionidæ it is rugose and warty: this you may see, particularly in that of Papilio Machaon. In many of the hawkmoths (Sphinx L.) it is covered with impressed puncta. In Attacus Io the upper side of the channels that separate the intermediate segments of the abdomen are curiously striated with transverse striæ, formed of very minute granula, the lower side being transversely sulcated. In some few instances, as in Arctia Salicis, Laria pudibunda and fascelina, the skin of the pupa is clothed with hair[576]: as is also that of Hesperia Bixæ, according to Madame Merian[577]. De Geer has described a little beetle under the name of Tenebrio lardarius (Latridius Latr., Corticaria Marsh.), the pupa of which is beset with very fine hairs, terminating in a spherical or oval button[578].

ii. I shall include under the same head both the figure or shape, and parts of pupæ, as the latter in most kinds are either the same or nearly the same as those of the larva, or merely incasing those of the imago, so as not to require that detailed notice that I judged necessary when treating of the parts of larvæ.

With regard to incomplete pupæ, nothing further can be said of their extremely various figure, than that it has a general resemblance to that of the perfect insect. The head, trunk, abdomen, and their respective external organs, are alike visible in both; but in the pupæ, the latter, instead of occupying their natural situation, are all closely folded under the breast and abdomen: or, as in the case of the long ovipositors of some Ichneumons, laid along the back. In a specimen of some coleopterous insect now before me, the following is the order of the arrangement of the parts:--The head is inflexed; the mandibulæ are open; between them are seen the labium and labial palpi; these appear to cover and conceal the maxillæ, and the maxillary palpi extend on each side beyond them; the antennæ pass above the thighs of the two anterior pair of legs, and then turning down over the breast between them and the posterior legs, repose upon the base of the wings; which also are turned down between the intermediate and posterior pair of legs, and rest upon the latter; the tibiæ are bent in and folded upon the thigh, and the tarsi turn outwards[579]. In another coleopterous species, the wings and elytra are placed under the hind-legs. In Hymenopterous pupæ the antennæ appear usually to lie between the legs[580]. In many Tipulæ the long legs are bent into three folds in the pupæ; but the tarsi are extended, and lie close to each other, the anterior pair being the shortest[581]. In a specimen belonging to this tribe in my cabinet, which I think contained Ctenocera pectinicornis, the six leg-cases are of the same length, exactly parallel and adjacent, and being annulated wear the appearance of tracheæ[582]. These parts have each their separate case, so that a pin may be introduced between them and the body: which cases, as well as the general envelope, are usually formed of a fine soft transparent membrane; but sometimes, as in the lady-bird (Coccinella), the tortoise-beetle (Cassida), the crane-fly (Tipula), &c. it is harder and more opaque, so that though it is usually easy for a practised Entomologist from an examination of the pupa, particularly in the Hymenoptera, to predict to what genus the insect to be disclosed from them will belong, yet in these cases the organs being not so conspicuous, a less experienced examiner might be perplexed, and unable to come to a conclusion.

Although hymenopterous pupæ have usually no parts but what are afterwards seen in the perfect insect, this is not the case with several coleopterous and dipterous ones, which are furnished with various temporary appendages, indispensable to them to bring about their final change, or for other purposes. Thus, the pupa of the male of Lucanus Cervus has two short, jointed anal processes[583]. That of Hydrophilus caraboides has a pedunculated lunulate one; and moreover, the sides of the abdominal segments, and the top of the thorax, are beset with hairs, which are not seen in the perfect insect[584]. The abdomen of many, also, is armed with spines. That, the arrangement of whose organs I lately described, has a quadruple series in the back of this part; viz. on each of the first five segments, 3, 2, 2, 3. The five first ventral segments also have on each side three spines; the inner are incurved, the intermediate nearly upright, and the outer one recurved. These spines, except those of the innermost ventral series, terminate in a bristle. In another coleopterous species the back part of the head is armed with a pair of lateral spines, and that of the thorax with three processes, the external ones armed with a single spine, and the intermediate one with a pair. De Geer has figured the pupa of an Asilus, the head of which is armed with eight spines--two robust ones in front, and three smaller ones, connected at the base on each side. The abdominal segments, also, are fringed with spines[585]. The abdomen of the pupa of Ctenocera pectinicornis is armed with several strong conical spines, pointing mostly towards the tail, which is likewise the case with that of Tipula lunata[586]. As the above pupæ are usually subterranean or subcortical, the spines assist in pushing them out of the ground, &c. The respiratory horns that proceed from the thorax of the pupæ of many of the aquatic gnats will be noticed in another place. Those of Corethra culiciformis and of some other aquatic gnat-like Diptera, have their anus furnished with a pair of oars, or natatory laminæ, by which they rise to the surface[587].

The figure of obtected pupæ, or chrysalises, is more uniform. They are commonly obtuse at the anterior extremity, and gradually contracted to a point at the posterior, or tail. The outline usually inclines to a long oval or an ellipse; but in some, as Attacus Io and Luna, the pupa is shorter and more spherical. In Geometra sambucaria it represents an elongated cone, and in Hepialus it is nearly cylindrical. In the butterfly tribe (Papilio L.) the outline is frequently rendered angular by various protuberances.

In all these pupæ may be distinguished the following parts:--first, the Head-case (Cephalo-theca), or anterior extremity; secondly, the Trunk-case (Cyto-theca), or intermediate part; and thirdly, the Abdomen-case (Gastro-theca).

1. The Head-case covers and protects the head of the inclosed imago. From its sides behind proceed the antennæ-cases (Cera-theca); and before from the middle, the tongue-case (Glosso-theca). Just below the base of the antennæ-case you may discern the eye-cases (Ophthalmo-theca), surrounded on their inner side by a crescent-shaped lævigated piece, which may perhaps transmit some light to the inclosed prisoner.

2. The Trunk-case, divided into the thorax, or upper surface, extending from the head to the dorsal segments of the abdomen, and consisting of three pieces, answering to the prothorax, mesothorax, and metathorax of the perfect insect: the first answering to the prothorax small, the second covering the mesothorax very large, and the two next representing the metathorax, at first appearing to belong to the abdomen, but having no spiracle; and the breast (pectus) or under-surface reaching from the head to the ventral abdominal segments, from which proceed the wing-cases (Ptero-theca) and leg-cases (Podo-theca), which organs, with the antenna-cases and tongue-case, entirely cover, or rather form, the breast. The arrangement of the whole is as follows:--The wing-cases, which are more or less triangular, and exhibit the larger nervures of the wings, are a lateral continuation of the mesothorax, which turn downwards from the sides of the breast, and cover, or replace, the three first ventral segments of the abdomen. The antenna-cases, united to the anterior portion of the head just behind the eye-cases, repose immediately next to those of the wings running parallel with their inner margin. Then follow the legs, the tibiæ forming an angle with the thigh, and the case of the anterior pair being innermost, and representing the breast-bone in the pupa. The tongue lies over the forelegs, except in the case of some sphinxes, which I shall notice afterwards: so that the glosso-theca covers both them and it.

3. The abdomen-case consists of nine segments when viewed on the back, and of only six when viewed below; so that it might be said to have ten dorsal and six ventral segments: but the fact is, that the place of the three anterior ventral segments, or rather ventral portions of the segments, (for they form complete rings without any lateral suture,) are replaced by the wings and other organs: in consequence of this, the fourth segment, which is less covered than the three first, at its posterior margin forms an annulus or ring. In counting the abdominal segments of a pupa, you must be careful not to include the piece that represents the metathorax, which looks as if it belonged to the abdomen[588]. In the pupæ of butterflies you will discover evident traces of ten dorsal segments; but in many moths, and some hawk-moths, you will perceive at first only eight, or even seven, but a closer examination will enable you to discover the line that marks out the others; and if you divide the puparium longitudinally, and inspect its internal surface, you will see very visible sutures between them. The intermediate segments are sometimes separated from each other and the preceding and subsequent ones by deep channels. In the pupa of Papilio Machaon there is one such channel between the third and fourth segments. In Bombyx regalis the channel is between the sixth and seventh, and in B. imperatoria there are three, namely, a channel between the third and fourth, and fourth and fifth, and fifth and sixth segments. The way in which insects with an exserted sting fold it in the pupa seems not to have been noticed; but from an observation of De Geer upon one species of Ichneumon, it appears to be turned up over the back of the abdomen[589].

These little animals, thus swathed and banded, exhibit no unapt representation of an Egyptian mummy; though Lamarck applies the term Mumia to incomplete pupæ[590], to which it seems less happily applicable.

Chrysalises, as to the modifications of their general figure, may be conveniently divided into two great classes: first, those that have no angular projections, the anal mucro of some excepted, on different parts of their body; and secondly, those which have such projections. Each of these classes affords variations in its peculiar characters which require to be noticed.

1. The first of these are called angular pupæ[591], and are confined to the Butterfly or diurnal tribes. In some the head projects into one short conical protuberance: this you may see in the chrysalis of the common cabbage butterfly (Pieris Brassicæ), and others of the same genus[592]; in the brimstone-butterfly (Colias Rhamni[593]), and in the beautiful purple emperor or high-flier (Apatura Iris F.[594]): though in this last it is not conspicuous. But the most remarkable instance of a single eminence from the head is exhibited by the pupa of a tropical butterfly (Morpho Idomeneus Latr.), figured by Madame Merian. In this the head projects into a long incurved obtuse horn[595]. In others the head is armed with two mucros, or conical eminences. This is the case with the common butterfly of the nettle (Vanessa Urticæ F.[596]), and with that of the beautiful Papilio Machaon[597]. In these the prominences are trigonal. These processes, which in some, as in the peacock-butterfly (Vanessa Io), stand upright[598], and in others diverge (Papilio Machaon), form the eye-cases of the included imago; and in their outer base is planted the crescent-shaped piece I lately mentioned, which seems intended to convey light into it. In many the prothorax, besides a lateral angular projection, has in the middle another triangular or trigonal one, somewhat resembling a Roman nose; on each side of which is a smaller elevated black point: so that it requires no great stretch of imagination to find out in it a sort of resemblance to the human face, which, though not quite so striking as honest Goedart figures it[599], is however very considerable. In the pupa of Morpho Menelaus, figured by Madame Merian[600], this nasiform prominence of the prothorax is extended into a long arched horn, reaching to the middle of the abdomen. The pupa of the silver-washed fritillary (Argynnis Paphia F.), and others of the same genus, exhibit beneath this nasiform prominence a very deep depression, itself beset with one or more series of smaller angular elevations. The back of the abdomen is often furnished with two rows of protuberances, in some species larger, in others smaller[601]; sometimes sharp and conical, and sometimes flat, and in some instances resembling the fins of fishes[602]. These bosses usually decrease in size towards the tail.

2. The second kind of chrysalises are denominated conical[603]. These, which include the crepuscular and nocturnal Lepidoptera, and the butterflies with onisciform larvæ, have no protuberances, and are less variable in their form--their anterior extremity being almost constantly oval and rounded, and their posterior conical and acute. An exception to this form is met with in the pupa of a moth long celebrated (Lasiocampa Pithyocampa)[604], which has the head acute and the tail obtuse, and armed with two points[605]. Another occurs in that of the Cossus, which has two points on the head, by which it makes an opening in its cocoon: when it assumes the imago, one of these is placed below the other[606]. And some few have the anterior end nearly flat instead of rounded. The pupa of the orange-tip butterfly (Pieris Cardamines) seems intermediate between the angular and conical kinds: it is somewhat boat-shaped, and distinguished by a fusiform process from the head and tail[607]. Other modifications of the usual figure are met with, but are for the most part so slight as not to require notice. One or two, however, should not be passed over. The pupæ of many hawk-moths (Sphinx L.) have the anterior piece of the head-case elongated into a sort of cylindrical proboscis, which is incurved beneath the breast: you will find this formation in S. Convolvuli and Ligustri[608]. In some, as in a species figured by Madame Merian, that feeds upon the Annona squamosa, it is rolled up like a serpent in many folds[609]. In Noctua Linariæ the tongue-case turns upwards, and is prominent laterally beyond the body[610]. This singular appendage is one of those beautiful instances of compensating contrivances, as Dr. Paley calls them, which perpetually occur in the insect tribes. The tongue of these hawk-moths is of very great length, often three inches, while the pupa itself is scarcely two; it could not possibly, therefore, have been extended at length, as it is in common cases, but is coiled up within the above protuberance. When the tongue is but a little longer than the breast, the ordinary plan is adhered to, but the apex of the breast projects a little over the abdomen into a sort of nose, in which the end of the tongue is contained. This conformation may be seen in the pupa of Noctua Gamma, Verbasci, and many other species. Sometimes, as in N. Linariæ F., this projection is recurved into a short horn.

I have before adverted to the adminicula or short spines looking towards the anus, with which the dorsal segments of the abdomen of some pupæ are armed; and by which, when the time for their exclusion is arrived, they are enabled to push themselves upwards or outwards from their several places of confinement[611]: you will find these in the pupa of the great goat-moth (Cossus ligniperda); and in the cylindrical pupa of the moth called the ghost (Hepialus Humuli F.) there are two rows of sharp triangular spines on the back of each segment. These are not laid flat, but, as they do also in the Cossus, form an acute angle with the body; which gives them greater power of resistance. Those that constitute the row nearest the base of the segment are longer than the anterior row, the middle spines than the lateral ones. The first and last segment are without them, and the last segment but one has a sharp ventral transverse ridge, armed with many sharp teeth[612]. The abdominal spines lately mentioned, of semicomplete pupæ, are also adminicula.

The tail of this description of pupæ is in many instances armed with a mucro, or sharp point, emerging from its upper side. You will see this in most hawk-moths. In the pupa of Hesperia Proteus the mucro is truncate at the apex; in that of Bombyx imperatoria it is long, and terminates in two diverging points. In the majority of chrysalises of both descriptions the tail is acute, and usually furnished with hooks of different kinds. These are so various in shape and number, &c. that they would probably afford good characters for discriminating many allied species. In some there are but two or three, in others five or six, in others they are more numerous[613]. Sometimes they are quite straight[614], but most commonly recurved, so as to form a hook. The hawk-moths, and a few others, as Bombyx Pini, Cerura Vinula, &c., have no anal hooks whatever. Under this head I shall observe, that in many conical pupæ below the anal angle or mucro, is the appearance of a vertical foramen or passage: this is particularly conspicuous in Hepialus, in which it is surmounted by a bifid ridge, and has under it a pair of minute black tubercles.

A pretty accurate judgement of the division to which the perfect insect when disclosed will belong, may usually be formed from the figure of its chrysalis. All the angular ones, with scarcely any exception, inclose butterflies. The converse, however, does not hold; for some that are not angular, as those of Parnassius Apollo and Mnemosyne, and most of the Linnean Plebeii urbicolæ, also inclose flies of that description. With these exceptions, all conical chrysalises give birth to moths or hawkmoths. An idea even of the family or genus under which the perfect insect will arrange, may be generally formed from the figure of the chrysalis; less distinctly, however, in the conical or rounded, than in the angular kinds, in which the prominences of the head and trunk, as before explained, usually vary in different families. Even the sex of some moths may be judged from the pupæ: those of females being thicker; and those also of the females that have no wings, or only the rudiments of them, will of course vary somewhat from the ordinary form: but there is a still more striking difference in that of Callimorpha? vestita F., and others of the singular tribe before noticed[615], called by the Germans Sacktrager (sack-bearers), from the sack-like cases in which the larva resides. The females of these having not only no wings, but no antennæ, and legs not longer than those of the larva, their pupa more resembles that of a dipterous than of a lepidopterous insect, it being not easy to determine which is the head and which the tail[616].

In these too we can often learn from the outline of the wing-cases, whether the inhabitant of the chrysalis has these organs indented or intire. If the former, the margins of these cases are sinuate, as in that of Vanessa C. album; if the latter, they are intire, as in Pieris Brassicæ. Even in conical pupæ,--the size, the shape of the antennæ, which may be distinguished through the skin that covers them, and slight modifications of the ordinary form,--give indications of the genus of the included insect sufficiently conclusive to a practised eye.

The true figure of coarctate pupæ when they are mature, the parts of the future fly being very visible, and each being included in a separate case[617], is that of those that belong to the incomplete division; but as this is a character not cognizable without dissection, it is customary, in speaking of pupæ of this description, to refer solely to the shape of the exterior covering, which is in fact a cocoon formed of the dried skin of the larva moulded into a different form. In this sense the figure of coarctate pupæ is extremely various. The majority of them are more or less oval or elliptical, without any distinct parts, were it not that they usually retain traces of the segments which composed the larva's body[618]. Of this figure are the pupæ of the common cheese-maggot[619], and many other flies. Others (Sepedon Latr.) have the pupa shaped like a boat. That of Scæva Pyrastri F. assumes the figure of a flask; or, according to Reaumur's more accurate comparison, of a tear[620]. The tail of many of these pupæ, particularly of aquatic species, is elongated into a sort of beak, either simple or forked, or is beset with spines variously arranged. The pupa of Stratyomis Chamæleon, and other allied species, differs from all the rest of this subdivision in retaining the exact form of the larva[621]; and hence constitutes an exception to the general character of our second great Division.

iii. There is much less variety in the colour of pupæ than in that of larvæ. The majority of coleopterous and hymenopterous pupæ are white, or whitish; of lepidopterous and dipterous, brown of various shades, often verging on black in the former and on red in the latter. The angular lepidopterous ones, however, are more gaily decorated. Some, Pieris Brassicæ, are of a greenish yellow, marked with spots of black; others are of a uniform green, Apatura Iris, Pieris Cardamines; others, reddish, Vanessa C. album; others again red with black spots, Urania Leilus[622]. A still greater number shine as though gilded with burnished gold--either applied in partial streaks, Vanessa Cardui; or covering the entire surface, Vanessa Urticæ. It was from this gilded appearance in some obtected pupæ that the terms Chrysalis and Aurelia were applied to the whole. The alchemists mistook this for real gold; and referred to the case as an argument in favour of the transmutation of metals. But Reaumur has satisfactorily shown, that in this instance the old proverb is strictly applicable--"All is not gold that glitters." He found that this appearance is owing to the shining white membrane immediately below the outer skin, which being of a transparent yellow gives a golden tinge to the former; in the same way that tinfoil, when covered with a yellow varnish, assumes the metallic appearance which we see in gilt leather. He mentions, too, that for the production of this effect--it is essential that the inner membrane be moist: whence may be explained the disappearance of the gilding as soon as the butterfly is ready to escape from the pupa. The shade of colour in these gilded chrysalises is various: some are of a rich yellow, like pure gold; others much paler; and some nearly as white as silver. That of Hipparchia Cassiæ F. is red with silver spots[623].

Though by far the greater number of the chrysalises of moths are of an uniform chestnut, brown, or black,--a few are of other colours; as that of Geometra alniaria, which is of a glaucous blue; of Noctua sponsa, lilac; and of Noctua pacta, of a lovely blue, caused by a kind of bloom, like that of a plum, spread upon a brown ground. A similar bloom is found on that of Parnassius Apollo, and on the anterior part of that of Platypterix cultaria and sicula; in which last, Kliemann observed it to the be renewed when rubbed off[624] Many pupæ have the sheaths of the wings of a different colour from that of the rest of the body; a few are variegated with paler streaks or bands, as Clostera Anastomosis, which has two red longitudinal stripes down its dark-brown back; and that of the common gooseberry and currant moth, which may be found in every garden, has alternate rings of black and yellow[625].

A few pupæ vary in their colour, as the painted lady-butterfly (Vanessa Cardui), some of which are light-brown with gray streaks and golden dots, others wholly of a golden yellow or brown, others of a light green[626].

Almost all at their first assumption of the pupa state have a different colour from that which they take a few days afterwards. This last they retain until the disclosure of the perfect insect; except some that have transparent skins, which a few days previously to this period exhibit the colours of the included animal.

iv. There is as great variety in the length of the age of Insects in their pupa as in their larva state. Some species continue in it only two or three days (Aleyrodes Chelidonii Latr., Tinea proletella L.); others, as many weeks, or months, or even years. Each, however, has in general a stated period, which in ordinary circumstances it neither much exceeds nor falls short of. The only general rule that can be laid down is--that small pupæ continue in that state a shorter time than those of larger bulk. Thus, amongst coleopterous genera, the more minute species of Curculio L.; amongst the Hymenoptera, the Ichneumones minuti L.; amongst the Lepidoptera, the subcutaneous tribes; and the majority of the Diptera,--remain as pupæ only a few days or weeks: while the larger species in all these orders commonly exist in the same state several months--many even upwards of two years. There are, however, numerous exceptions to this rule; for some large pupæ are disclosed in a much shorter time than some others not a twentieth part of their bulk.

The reasons both of the rule and of the exceptions to it are sufficiently obvious. And first, as to the rule:--If you open a pupa soon after its assumption of that state, you will find its interior filled with a milky fluid, in the midst of which the rudiments of its future limbs and organs, themselves almost as fluid, swim. Now the end to be accomplished during the pupa's existence is, the gradual evaporation of the watery parts of this fluid, and the development of the organs of the inclosed animal by the absorption and assimilation of the residuum. Reaumur, by inclosing a pupa in a stopped glass tube, collected a quantity of clear and apparently of pure water, equal to eight or ten large drops, which had evaporated from it, and was condensed against the sides of the tube, and it was found to have lost an eighteenth part of its weight[627]. It is plain, therefore, that this necessary transpiration, other circumstances being alike, must take place sooner in a small than in a large pupa. Next, as to the exceptions:--Since the more speedy or more tardy evaporation of fluids depends upon their exposure to a greater or less degree of heat, we might à priori conclude, that pupæ exposed to a high temperature would sooner attain maturity, even though larger in bulk, than others exposed to a low one:--and this is the fact. The pupa of a large moth, which has assumed that state in the early part of summer, will often disclose the perfect insect in twelve or fourteen days; while that of an Ichneumon, not one hundredth part of its size, that did not enter this state till late in autumn, will not appear as a fly for seven or eight months. But this is not the whole. The very same insect, according as it has become a pupa at an earlier or later period of the year, will at one time live but a few weeks, at another several months, in that state. Thus, if the caterpillar of Papilio Machaon, one of those which has annually a double brood, becomes a pupa in July, the butterfly will appear in thirteen days: if not until September, it will not make its appearance until the June following; that is, not in less than nine or ten months: and the case is the same with the pupæ of Noctua Psi, and of a vast number of other insects. To put beyond all doubt the dependence of these remarkable variations on temperature merely, it was only necessary that they should be effected, as Lister long ago advised[628], by artificial means. This Reaumur accomplished. In the month of January he placed the chrysalises of several moths and butterflies, which would not naturally have been disclosed until the following May, in a hothouse: the result was, that the perfect insects made their appearance in less than a fortnight, in the very depth of winter; and by other numerous and varied experiments he ascertained, that in this heated atmosphere five or six days hastened their maturity more than as many weeks would have done in the open air. The disclosed insects were in every respect perfect, and the females, after pairing, laid their eggs, and then died, just as if they had not been thus prematurely forced into existence. The converse of this experiment equally succeeded:--by keeping pupæ the whole summer in an icehouse, Reaumur caused them to produce the fly one full year later than their ordinary period[629].

This extraordinary fact leads us to a very singular and unexpected conclusion--that we have the power of lengthening or shortening the life of many insects at pleasure; that we can cause one individual to live more than twice as long as another of the same species, and vice versâ. Had Paracelsus made this discovery, it would have led him to pursue his researches after the elixir of immortality with redoubled confidence, and would have supplied him with an argument for the possibility of prolonging the life of man beyond its usual term, which his sceptical opponents would have found some difficulty in rebutting. Even the logical Reaumur seems inclined to infer from it, that this object of the alchemists was not so chimerical as we are wont to conclude[630]. He confesses, however, if it were to be attained only by the same process as effects the extension of an insect's life--by prolonging its state of torpor and insensibility,--that few would choose to enjoy it on such conditions. The man of pleasure, blunted by excess of use to all modern stimuli, might perhaps not object to a sleep of a hundred years, in the hope of finding something new under the sun when he waked; and an ardent astronomer would probably commit himself with scientific joy to a repose as long and as sound as that of the seven sleepers, for the chance of viewing his predicted return of a comet, on stepping out of his cave: but ordinary mortals would consign themselves to the perils of so long a night with reluctance, apprehending a fate no better than what befel the magician, who ordered himself to be cut in small pieces and put in pickle, with the expectation of becoming young again[631].

The duration, then, of an insect's existence in the pupa state, depends upon its bulk, upon the temperature to which it is exposed, and upon a combination of these two circumstances. This experiment appears very simple. We seem to ourselves to have accomplished what is so often undertaken in vain--to have found an entrance into the cabinet of Nature, and to have made ourselves masters of the contents of one of the pages of her sealed and secret book. We deceive, ourselves, however: this book, when it seems most legible, is often interlined with sympathetic inks, if I may so speak, which require tests unknown to us for their detection. If you lay up a considerable number of the pupæ of a moth now called Eriogaster lanestris, the larva of which is not uncommon in June on the black-thorn, selected precisely of the same size, and exposed to exactly the same temperature, the greater number of them will disclose the perfect insect in the February following; some not till the February of the year ensuing, and the remainder not before the same month in the third year[632]. Mr. Jones of Chelsea, a most acute lepidopterist, in one of his excursions captured a female of Arctia mendica, another moth, which laid a number of eggs, thirty-six of which produced caterpillars: all these fed, spun their cocoons, and went into the pupa state in the usual manner, but at the proper season only twelve produced the fly. As this was no uncommon circumstance, he concluded that the rest were dead: to his great astonishment, however, in the next season twelve more made their appearance; and the following year the remainder burst into life, equally perfect with the foregoing[633]. In this extraordinary result, which also occasionally has been observed to take place in the emperor-moth (Saturnia pavonia), the privet-hawkmoth (Sphinx Ligustri), and that of the spurge (S. Euphorbiæ)[634], and other species,--it is clear that something besides mere size and temperature is concerned: for, these circumstances being precisely alike, one pupa arrives at maturity in six months, and another of the same brood requires between two and three years. We can guess, that the end which the All-wise Creator has in view, in causing this remarkable difference, is the prevention of all possibility of the destruction of the species. Eriogaster lanestris and Arctia mendica, &c., for instance, are doomed, for some reason unknown to us[635], to be disclosed from the pupa in the cold and stormy months of February and March, almost every day of which in certain years is so ungenial that few insects could then survive exposure, much less deposit their eggs and ensure the succession of a progeny. Now, were all these to make their appearance in the perfect state in the same year, it might happen that the whole race in a particular district would be destroyed. But this possibility is effectually guarded against by the beautiful provision under consideration, it being very improbable that three successive seasons should be throughout unfavourable; and without such occurrence, it is clear that some of the race of this moth will be preserved. In the case of other moths, whose pupæ though disclosed in the summer are governed by the same rule, the prevention of the extinction of the species, by any extraordinary increase in a particular year of their natural enemies, seems the object in view[636]. But though the intention be thus obvious, the means by which it is effected are impenetrably concealed. What physiologist would not be puzzled with the eggs of a bird, of which one-third should require for their hatching to be sat upon only a fortnight, another third a month, and the remainder six weeks? Yet this would be an anomaly exactly analogous to that observed by Mr. Jones with respect to the pupæ of A. mendica. Reaumur found that when the skin of pupæ was varnished, so as to prevent absorption, the appearance of the fly happened nearly two months later than in ordinary circumstances. Are we to conjecture that those of the moth just mentioned, or of E. lanestris, that are latest matured, from a greater degree of viscidity in the fluid that forms them[637], have thicker and more impervious skins than those disclosed at an earlier period? Or are we to refer the difference to some unknown peculiarity of organization? On any supposition, the fact remains equally wonderful; and I know of none the illustration of which is more worthy of the patient investigation of the physiologist.

As the period of maturity of the perfect insect is thus in some cases not fixed even to years, and as in many it seems dependent upon such variable causes; nothing appears more improbable than that it should ever be so strictly determined, that even the week in which the fly will leave its pupa-case can be pretty accurately predicted. Such, however, is the fact with regard to the Ephemera so interestingly described by Reaumur, the myriads of which that issue from the banks of the Seine all appear in two or three days, somewhere between the 10th and 18th of the month of August[638] in every year; at which time the fishermen regularly expect them. A like regularity attends the appearance of those described by Swammerdam, which every year, for three days about the feast of St. John, issue in clouds from the Rhine[639]--Not only is the week fixed, but in several instances even the hour. The Ephemeræ observed by Reaumur appear at no other time than between eight and ten o'clock in the evening; and so unalterably is their exclusion fixed, that neither cold nor rain can retard it. Between these hours, in the evenings on which they appear, you may see them fill the air, but an hour before or after, you will in vain look for one[640]. So also the silkworm-moth and the hawkmoth of the evening primrose (Sphinx Œnotheræ) constantly break forth from the pupa at sunrise: and the hawkmoth of the lime (Smerinthus Tiliæ) as certainly at noon[641]. Schroeter states, that of sixteen specimens of the death's-head-hawkmoth (S. Atropos) which he bred, every one was disclosed between four and seven o'clock in the afternoon[642].

Before I conclude this head, I must observe, that after a caterpillar or gnat has spun its cocoon, it sometimes remains for a considerable period before it incloses itself in the pupa-case, and casts off the form of a larva. Thus the little parasite (Ichneumon glomeratus L.) that destroys the caterpillar of the common cabbage-butterfly, remains a larva in its cocoon for many months, but it becomes a perfect insect a few days after it has put on its puparium[643]; and the caterpillars of the great goat-moth (Cossus ligniperda), if they spin their cocoon in the autumn, remain in it through the winter in the larva state; whereas, if they inclose themselves in the month of June, they assume the pupa, so as to appear as flies in three or four weeks[644]. It is not therefore easy to state precisely the age of those pupæ which are produced from larvæ that spin cocoons.

v. I have not much to say with regard to the sex of pupæ. The male is probably to be distinguished from the female by being smaller; but in the first great division of pupæ, those which resemble the larvæ, and are locomotive, the female in numerous cases may be known by the Ovipositor, or instrument for depositing her eggs in their proper station: and the male also has his anal instruments. Sometimes in this state the animal is so matured, as to be capable of continuing its kind. I have found the pupæ both of a Gryllus L. and of a Cimex L. in coitu.

vi. Though the pupæ of the second great division are usually not locomotive, yet I must not omit some notice of their motions. As the legs of insects in this state are folded within a common or partial integument, of course none of the pupæ now under consideration, with the exception of those of the Trichoptera order, can walk: coarctate ones are even incapable of the slightest motion, and exhibit no symptom whatever of animation. Some of those that are termed incomplete, however, and most chrysalises, have the power of communicating to their bodies a slight movement, extending more or less in different species, which is effected by the abdominal segments solely. The latter, during the first twelve hours of being pupæ, when their skin is soft, frequently turn themselves, that the side on which they lie may not be flattened; afterwards by far the majority merely wriggle or twist their abdomen when touched, or in any way incommoded or disturbed. We learn from De Geer, that the pupa of the ghost-moth (Hepialus Humuli), the cocoon of which is more than twice the length of the chrysalis, moves in it from one end to the other[645]. Bonnet observed one of a moth (perhaps Lasiocampa Quercus), which alternately fixed itself at the top and bottom of its spacious and obliquely-fixed cocoon; descending slowly, but ascending as quickly, and almost in the same manner, as a chimney-sweeper in a chimney[646]. The pupa of the weevil of the water-hemlock (Lixus paraplecticus) will move from one end of the interior of a branch to another by means of its adminicula, aided by the motion of its abdominal segments[647]. But the most locomotive of pupæ of the second division are those of gnats, and many Tipulidans, which pass this state in the water. These will move from the bottom to the surface, and back again, with great facility and velocity. I have before mentioned several other motions of pupæ[648], which I shall not repeat here, by which they extricate themselves from their several places of intermediate repose, before they leave the puparium: if the imago were to be disclosed in the interior of a tree, or in the earth, its wings would be materially injured in forcing its way out. The object of several of the above motions may be to alarm insects that might attack these defenceless beings. The twirling motion in particular, formerly noticed[649], in some species, by causing a rustling against the sides of the cocoon, makes a considerable noise--so singular in that of a red underwing-moth (Noctua pacta), that Rösel tells us, (who by the by was more timid than becomes a philosopher,) that the first time he heard it, he had nearly thrown away the box that contained it, in his fright[650].

vii. We are next to consider The extrication of the perfect insect from the puparium, or pupa-case, and from the cocoon. The period when the pupa has attained maturity, and the inclosed insect is ready to burst the walls of its prison, may be often ascertained. Just at this time the colour frequently undergoes an alteration, the golden or silver tint of the gilded chrysalises vanishes; and those which are transparent, usually permit the form and colours of the insect within and the motions of their limbs to be distinctly seen through them. In the Libellulina the eyes become more brilliant[651]. The mature pupæ of the moth lately mentioned (Eriogaster lanestris) have a particular swell of the abdominal segments, not apparent in those that are to continue till another season, or longer[652]. Those of the case-worms (Trichoptera) push off the grates from the cases which they have hitherto inhabited, and swim about[653]. Other signs and motions doubtless predict the approach of this great change in other species, which have not been recorded.

The mode in which insects make their way out of the puparium differs in different orders. In obtected pupæ, the struggles of the included butterfly or moth first effect a longitudinal slit down the middle of the thorax, where there is usually a suture for the purpose. The slit rapidly extends along the head, and down the parts which compose the breast, and the insect gradually withdraws itself from its case. It is not, however, from the outer skin merely that it has to disengage itself, but also from a series of inner membranous cases, which separately inclose the antennæ, proboscis, feet, &c., as a glove does the fingers; and similar cases inclose the parts of the perfect insect in pupæ of all the other orders. This is sometimes a work of difficulty, but ordinarily it is effected with ease.

Incomplete and semicomplete pupæ undergo nearly the same process, save that in them the body is not swathed up in a common case; and therefore they have only to liberate themselves from the partial cases that envelop the several parts of their body.

In coarctate pupæ, as those of Muscidæ, Syrphidæ, Œstridæ, &c., the process is different. Their outer-case is ordinarily more rigid and destitute of the sutures, which in the former tribes so easily yield to a slight effort. Yet in these, at the anterior end under which the head of the fly lies, and from which it always issues, there is commonly a sort of lid, joined by a very indistinct suture to the rest, which can be pushed off, leaving a sufficient opening for the egress of the insect. In the pupæ of many of this tribe this lid is composed of two semicircular pieces, which can be separately removed. Many species seem to be able to force off the lid of their puparium, by merely pushing against it with their heads: but the common flesh-fly and many other Muscidæ, which are perhaps too feeble to effect this, or whose puparia are stronger than ordinary, are furnished with a very remarkable apparatus for this express and apparently sole purpose. They are gifted with the power of introducing air under the middle part of the head, to which the antennæ are fixed, and of inflating that part into a sort of membranous vesicle as big as the head itself; by the action of which against the end of the pupa-case, the lid is soon forced off. So powerful is this singular lever, that it is even sufficient to rupture the fibrous galls in which the pupæ of the gay-winged Tephritis Cardui[654] are inclosed. That it is designed by Creative Wisdom to answer this sole purpose seems proved, from its disappearing soon after the disclosure of the fly, whose head shortly becomes all alike hard. Reaumur suspects that it may also be intended to promote the circulation of the insect's fluids; but to me his reasons appear not conclusive[655]. In one instance a mode still more unexpected obtains. The illustrious naturalist just named found that the fly which proceeded from one of the rat-tailed grubs (Elophilus Latr.) had actually the power of completely reversing its situation in its narrow case; and that it then employed its tail in pushing off the lid, which other species remove by means of their heads[656].

The extrication of insects whose pupæ are above ground, like those of butterflies, many beetles, flies, &c., is comparatively a simple operation. But what, you will ask, becomes of those species whose pupæ are concealed deep in the earth, or in the heart of the trees on which their larvæ have fed? Of this you shall be informed.--Coleopterous insects disclosed from pupæ thus circumstanced, wait until their organs have acquired strength, and their elytra are sufficiently hardened to protect their filmy wings from damage in forcing their way through the earth or wood which covers them. Thus Oryctes nasicornis, a rhinoceros beetle common on the Continent, is a full month before it reaches the surface of the earth, after quitting its puparium. But it is evident that no delay would enable lepidopterous or dipterous insects, which are without elytra, to make their way out of such situations, without irreparable injury to their delicate wings. Many of these, therefore, while still within the hard case of the pupa, have the precaution, a few days previously to their exclusion, to force themselves up to the surface of the earth, or, when they reside in the interior of trees, to the entrance of their hole. This is effected by a successive wriggling of the abdominal segments, which in several species, of the Coleoptera, Lepidoptera, and Diptera orders, for this purpose, as has been more than once observed[657], are furnished with sharp points (adminicula), admitting a progressive, but not a retrograde motion. The puparia of the great goat-moth (Cossus ligniperda) may be often seen projecting from orifices in willow-trees; and those of the common crane-fly (Tipula oleracea) from the surface of the earth, to which they have thus made their way from a depth of several inches.

In all the preceding instances the exclusion of the perfect insect is complete, as soon as it has withdrawn itself from the puparium. But to a very large number, even after this is effected, the arduous task still remains of piercing the cocoons of leaves, of thick silk, of tough gum, or even of wood, in which the pupæ are incased. We can readily conceive how the strong jaws of coleopterous and hymenopterous species may be employed to release them from their confinement. But what instruments can be used for this purpose by moths in a state of great debility, whose mouth has nothing like jaws--merely a soft membranous proboscis? How shall the silkworm-moth (B. Mori) force its way through the close texture of a silken ball, through which the finger could not be easily pushed? Or the puss-moth (Cerura Vinula) pierce the walls of its house of glue and wood, which scarcely yield to the knife? You will not doubt that these difficulties have been foreseen by INFINITE WISDOM, and provided against by INFINITE POWER. The egress of moths from their cocoons is secured in two ways;--either by some peculiarity in the first construction of the cocoon by the caterpillar, or by some process which the pupa or perfect insect is instructed to perform. As examples of each, several curious instances may be cited.

The larva of the moth which about 1760 made such havoc in the province of Angoumois in France, becomes a pupa in the interior of the grain of wheat which it has excavated; but the opening by which it first entered is not bigger than a pin's point, and is quite insufficient for the egress of the moth. How, then, is the latter to force its way through the tough skin which surrounds it? The larva, previously to assuming the pupa state, gnaws out a little circular piece at that end of the grain where the head of the future moth would lie, taking care not to detach it entirely. At this little door, which is sufficient to protect it from intruders, the moth has but to push, when it falls down, and leaves a free passage for its exit. A contrivance almost similar is adopted by a caterpillar which feeds in the interior of the heads of a species of teazel (Dipsacus L.), for a minute and interesting history of which we are indebted to Bonnet. This caterpillar previously to its metamorphosis actually cuts a circular opening in the head, sufficiently large for the egress of the future moth; but to secure this sally-port during its long sleep, it artfully closes it with fibres of the teazel, closely but not strongly glued together[658]. Another small caterpillar described by the same author, resides in the leaf of an ash curiously rolled up into a cone, and then assumes the pupa, which is inclosed in a silken cocoon, ingeniously suspended by two threads like a hammock in the middle of its habitation, and of so slight a texture that it presents no obstacle to the extrication of the moth. It is the closely-joined sides of its leafy dwelling that form a barrier, which, were it not for the precaution of the larva, would be impenetrable to so small and weak an animal. The little provident creature, before its change to a pupa, gnaws in the leaf a round opening, taking care not to cut through the exterior epidermis. This door is to serve the moth for its exit, like that formed by the wheat-caterpillar. But in proportion to its bulk its verdant apartment is of considerable size. How then shall the moth know the exact place where its outlet has been traced? How, without a clue, shall it discover in its dark abode the precise circle which requires only a push to throw it down? Even this is foreseen and provided against. Out of twenty positions in which its hammock might have been slung, the caterpillar has been directed so to place it, that the silken cord that suspends the head is fastened close to the side of the door which it has previously constructed; and the moth, guided by this filum ariadneum, at once makes its way out of an apartment which, but for this contrivance, might have been to it a labyrinth as inextricable as that of Minos[659].

The mode in which other caterpillars provide for their extrication, when become moths, from their silken cocoons, is not less ingenious. Those of Eriogaster lanestris (of which I have lately said so much,) and others, form oblong cocoons, which, viewed externally, you would at the first glance assert were of one solid piece: but on examining them more narrowly, you perceive one end of them to be a distinct lid, of a size large enough to permit the moth to issue out; and that it is kept in its place by a few slight threads, easily broken by pressure from within[660]. A few pages back[661] I mentioned a cocoon formed by the larva of Tortrix prasinana, of the shape of a boat reversed, composed of two inclined walls fastened together at the top and ends. In constructing this cocoon, it firmly glues to each other the top and one end, so as to form an impermeable suture; but the other end, at which the moth is to issue, though externally it seems as strong as the rest, is merely drawn close by a slender thread or two fastened on the inside, and easily broken from within. And, what is particularly singular in the construction of this ingenious habitation, the sides forming the end last mentioned, though originally requiring force to draw them into their required position, become so elastic as to close again when the moth has passed between them and made her escape; the cocoon preserving its usual shape, even when deprived of its inhabitant[662]. A similar cocoon is constructed by another leaf-rolling caterpillar, that of Tortrix chlorana[663]. Many similar proofs of contrivance in the construction of silken cocoons might be adduced, but I shall confine myself to one more only--I mean that furnished by the flask-shaped brown one of Saturnia Pavonia, and some other moths. If you examine one of these cocoons, which are common enough in some places on the pear-tree or the willow, you will perceive that it is generally of a solid tissue of layers of silk almost of the texture of parchment; but at the narrow end, or that which may be compared to the neck of the flask, that it is composed of a series of loosely-attached longitudinal threads, converging, like so many bristles, to a blunt point, in the middle of which is a circular opening[664]. It is through this opening that the moth escapes. The silk of its cocoon is of so strong a texture and so closely gummed, that had both ends been similarly closed, its egress would have been impracticable; it finds, however, no difficulty in forcing its way through the aperture of a sort of reversed funnel, formed of converging threads that readily yield to pressure from within. But an objection will here probably strike you. You will ask, Is not this facility of egress purchased at too dear a rate? Must not a chrysalis in an open cocoon be exposed to the attacks of those ichneumons of which you have said so much, and of numerous other enemies, which will find admittance through this vaunted door? Our caterpillar would seem to have foreseen your dilemma; at least, under heavenly guidance, she has guarded against the danger as effectually as if she had. If you cut open the cocoon longitudinally, you will see that within the exterior funnel-shaped end, at some distance she has framed a second funnel, composed of a similar circular series of stiff threads, which, proceeding from the sides of the cocoon, converge also to a point, and form a sort of cone exactly like the closed peristome of a moss; or, to use a more humble though not less apt illustration, like the wires of certain mousetraps[665]. In this dome not the slightest opening is left, and from its arched structure it is impenetrable to the most violent efforts of any marauders from without; whilst it yields to the slightest pressure from within, and allows the egress of the moth with the utmost facility. When she has passed through it, the elastic threads resume their former position, and the empty cocoon presents just the same appearance as one still inhabited. Rösel relates with amusing naïvété how this circumstance puzzled him the first time he witnessed it: he could scarcely help thinking that there was something supernatural in the appearance of one of these fine moths in a box in which he had put a cocoon of this kind, but in which he could not discover the slightest appearance of any insect having escaped from it, until he slit it longitudinally[666]. But from an observation of Meinecken, it appears that these converging threads serve a double purpose; being necessary to compress the abdomen of the moth as it emerges from the cocoon, which forces the fluids to enter the nervures of the wings, and give them their proper expansion. For he found, that when the pupa is taken out of the cocoon, the moth is disclosed at the proper time, but remains always crippled in its wings; which never expand properly, unless the abdomen be compressed with the finger and thumb, so as to imitate the natural operation[667].

I am next to give you some account of the second mode in which the release of the perfect insect from its cocoon is effected--that, namely, wherein its own exertions chiefly accomplish the work. I shall from a large number select only a few instances. The texture of the cocoon of the silkworm-moth is uniform in every part, and the layers of silk are equally thick at both ends. The moth makes its way out by cutting or breaking these threads at the end opposite to its head: an operation which, as it destroys the continuity of the silk, those who breed these insects are particularly careful to guard against, by exposing the cocoon to heat sufficient to destroy the included pupa. The question is--What instruments does the moth employ to effect this? And this we are not able to answer satisfactorily. Malpighi asserts that the animal first wets the silk with a liquid calculated to dissolve the gum that connects the threads, and then employs its lengthened head to push them aside and make an opening[668]. But, as Reaumur has observed, besides that so obtuse a part as the head of a moth is but ill fitted to act as a wedge, we find the threads not merely pushed to each side, but actually cut asunder. He therefore infers that the eyes, which are the only hard organs of the head, are the instruments by which the threads are divided--their numerous minute facets serving the purpose of a fine file[669]. It should be observed, however, that Mr. Swayne confirms Malpighi's assertion, that the silkworm does not cut, but merely pushes aside, the threads of its cocoon; and he informs us that he has proved the fact, by unwinding a pierced cocoon, the thread of which was entire[670]. Yet Reaumur's correctness cannot be suspected: and he affirms, that from observation there can scarcely be a doubt that most of the threads are broken[671]; which is further confirmed in an account of the breeding of silk-worms published in the American Philosophical Transactions: in which it is expressly stated, that cocoons out of which the fly has escaped, cannot be wound[672]. Analogy, it must be confessed, is against Reaumur's opinion; since other kinds of silkworms make their escape by means of a fluid. Thus we are informed by Dr. Roxburgh, that Attacus Paphia, when prepared to assume the imago, discharges from its mouth a large quantity of liquid, with which the upper end of the case is so perfectly softened, as to enable the moth to work its way out in a very short space of time,--an operation which, he says, is always performed in the night[673]. Perhaps the two opinions may be reconciled, by supposing the silkworm first to moisten and then break the threads of its cocoon. In those that are of a slighter texture, a mere push against the moistened end is probably sufficient: and hence we find in so many newly disclosed moths the hair in that part wet, and closely pressed down[674]. If it be apparently difficult for the silkworm-moth to effect an opening in its cocoon, how much harder must seem the task of the puss-moth (Cerura Vinula) to pierce the solid walls of its wood-thickened case? Here the eyes are clearly incompetent; nor could any ordinary fluid assist their operation, for the gum which unites the ligneous particles is indissoluble in aqueous menstrua. You begin to tremble for the fate of the moth incarcerated in such an impervious dungeon--but without cause: what an aqueous solvent cannot effect, an acid is competent to: and with a bag of such acid our moth is furnished. The contents of this she pours out as soon as she has forced her head through the skin of the chrysalis, and upon the opposite end of the cocoon. The acid instantly acts upon the gum, loosens the cohesion of the grains of wood, and a very gentle effort suffices to push down what was a minute ago so strong a barrier. How admirable and effectual a provision! But there is yet another marvel connected with it. Ask a chemist, of what materials a vessel ought to be to contain so potent an acid: he will reply,--of glass. Yet our moth has no glass recipient: her bottle is a membranous bag; but of so wonderful a fabric as not to be acted upon by a menstruum which a gum, apparently of a resinous nature, is unable to resist! This fact can only be explained by the analogous insensibility of the stomach to the gastric juice, which in some animals can dissolve bone,--and it is equally worthy of admiration. In both cases, the vitality of the membranous or fleshy receptacle secures it from the action of the included fluid; but how--who shall explain?

Ordinarily it is the moth that breaks the cocoon; but in the goat-moth and many Tortrices it is the pupa itself that performs the work, either wholly or partially. The pupa of the former is for this purpose furnished with sharp points upon the head, capable of effecting this object[675]. The locust-moth, another species of Cossus (C. Robiniæ Peck), whose history has been admirably detailed by Professor Peck, has a different process. "In the silk-moth," says he, "and all others which I have had opportunity to observe, the chrysalis bursts in the cocoon, and the fluid which surrounded the new insect in it escaping at the same time, so weakens or dissolves the fibre and texture of the silk, that the moth is able to extricate itself, leaving the chrysalis behind it; but this is not the manner in the locust-moth. After remaining till all its parts are fully grown and it is ready to quit its prison, a certain quantity of exercise is necessary, to break the ligaments which attach the moth to the shell of the chrysalis, and to loosen the folds of the abdomen. In taking this exercise, it can only move the abdomen in various directions: as one side of the rings is moved forward, the hooks in the serrated lines above mentioned (the adminicula) take hold of the silk, and prevent their sliding back; the next flexure brings forward the opposite side of the rings, which are prevented by the points on that side from slipping back in the same manner, and the chrysalis is forced out of the slightly woven extremity of the cocoon, and through the silk-lined cavity, till it is protruded for about one-third of its length out of the opening in the bark, and into the air[676]."

An exception to the general rule--that the rupturing of the cocoon is the business of the inclosed insect itself--is met with amongst ants; the workers of which not only feed the young, but actually make an aperture in their cocoons, cutting the threads with their mandibles with admirable dexterity and patience, one by one, at the time they are ready to emerge, the precise period for which these indefatigable nurses are well aware of, that they may meet with no obstacle. Without this aid, the young ant would be unable to force its way through the strong and dense coating of silk that infolds it[677]. And a proceeding somewhat akin to this was observed by the Hon. Captain Percy, R.N., who himself related it to me. Being fond of the study of insects, he was in the habit of attending to their motions; and in the beginning of September 1821 noticed those of a number of female Tipulæ, probably T. oleracea L., busily engaged in depositing their eggs amongst the roots of grass. While observing these proceedings, he at the same time saw one quitting its pupa-case, which had already by its own efforts got its head, thorax, and anterior legs out of it. It was then joined by two male flies; which, with their anal forceps and posterior legs taking hold of the pupa-case, appeared with their mouths and anterior legs to push the little prisoner upwards, moving her backwards and forwards; and as they kept raising her, shifting their hold of the skin till she was entirely extricated, when they left her to recover her strength by herself. Probably the extreme length of the two pair of hind-legs of these animals may render such assistance necessary for their extrication.

There remains yet to be explained under this head the manner in which the perfect insect is excluded from certain aquatic pupæ; such as those of Phryganeæ, gnats, and one of those Tipulidæ that resemble gnats. These pupæ (perhaps that they may be safe from the attack of birds) are destined to remain during the greater part of their existence in this state at the bottom of the water. But it is obvious that if the perfect insects were there to be disclosed, their wings would be wetted, and they would be drowned. It is the provision by which this result is obviated that now calls for your attention.

You have already been told that the larvæ of Phryganeæ inclose themselves in cases of different materials, open at each end[678]. You have also learned, that in becoming pupæ, they secure each end of their cases with a grating of silk[679]. When that change has occurred, they remain motionless at the bottom of the water. Now how are these pupæ, encased in tubes of a greater specific gravity than the surrounding fluid, to make their way to the surface when the time has arrived for their becoming denizens of the air? This they accomplish in the following manner:--The pupa is furnished with two strong exterior moveable mandibuliform processes, and has the power of moving its four anterior legs and antennæ while in the pupa-case. With these temporary jaws it makes an opening in one of the silken doors of its case, forces its way out at that end, and then by moving its legs, the cases of which in some species are ciliated for this very purpose, swims to the surface, where its skin splits, and discloses the included insect. That these jaws are given for the express and exclusive purpose of being thus applied, seems undeniable. The pupa eats nothing--they are therefore in every other point of view superfluous. They are given to it alone of all other similar pupæ, because unnecessary to all others; and they are cast off along with the rest of the puparium, the perfect insect having no vestige of jaws[680].

The gnat has to undergo its change on the surface of the water--How is it to accomplish this without being wetted? In the pupa state they usually remain suspended with the posterior end of the body turned downwards: but when the period for its change is arrived, it stretches it out upon the surface, above which its thorax is elevated. Scarcely has it been a moment in this position, than, swelling out the interior and anterior parts of the thorax, it causes it to split between the two respiratory horns. Through this opening the anterior part of the gnat then emerges. As soon as the head and trunk are disengaged, it proceeds with its labour, and gets out more and more; elevating itself so as to appear in the puparium like a mast in a boat. As it proceeds, the mast is more and more elevated and lengthened, till it becomes nearly perpendicular--just as the mast of a boat is gradually raised from a nearly horizontal to a vertical position: at this period a very small portion of the abdomen remains in the puparium. Neither its legs nor wings are of any use in maintaining it in this position. The latter are too soft, and, as it were, folded; and the former are stretched out along the abdomen--the segments of this last part are the only agents. The observer who sees how the little boat gradually sinks, and how its margin approaches the water, forgets the mischievous insect it contains, which at another time he would crush without remorse, and becomes interested for its fate; especially should wind agitate the water. A very little is sufficient to drive about rapidly the little voyager, since it catches the wind in some degree as a sail. If it should be upset, it would be all over with it;--and numbers do thus perish. The gnat, after having fixed itself thus perpendicularly, draws first its two anterior legs out of their case, and moves them forward, and next the two intermediate ones; then inclining itself towards the water, it rests its legs upon it, for water is to them a soil sufficiently firm and solid to support them, although surcharged with the weight of the insect's body. As soon as it is thus upon the water, it is in safety; its wings unfold themselves and are dried, and it flies away. All this is the work of an instant[681].

The pupæ of Chironomus plumosus proceed from those red worm-like larvæ so common throughout the summer in tubs of rain-water, &c., described by Reaumur[682]. They are not inclosed in cases, but are of a greater specific gravity than the water at the bottom of which they reside, until within a few hours of the exclusion of the fly. They have the power of swimming, however; and by moving the tail alternately backwards and forwards, can slowly raise themselves to the top of the water. But here occurs a difficulty. For the extrication of the imago it is necessary that they should remain quietly suspended at the surface; and moreover that the thorax, in which the opening for its exit is to be made, should be at least level with it: and this is precisely what takes place. If you watch one of these pupæ when it ascends from the bottom, you will see that as soon as it has reached the top it remains suspended there motionless; and that its thorax is the highest part of the body, and level with the surface. Now the question is, in what way this is accomplished? How can a pupa of greater specific gravity than water, remain suspended without motion at its surface? and how can its thorax, which is at its heaviest end, be kept uppermost?--By a most singular and beautiful contrivance, which I shall explain; the more particularly because it has escaped Reaumur, and, as far as I know, all other entomological observers. The middle of the back of the thorax has the property of repelling water--apparently from being covered with some oily secretion. Hence, as soon as the pupa has once forced this part of its body above the surface, the water is seen to retreat from it on all sides, leaving an oval space in the disk, which is quite dry. Now though the specific gravity of the pupa is greater than that of water, it is but so very slightly greater, that the mere attraction of the air to the dry part of the thorax, when once exposed to it, is sufficient to retain it at the surface; just as a small dry needle swims under similar circumstances. That this is a true solution of the phænomenon, I am convinced by the result of several experiments. If, when the pupa is suspended at the surface, a drop of water be let fall upon the dry portion of the thorax, it instantly sinks to the bottom,--the thorax, which belongs to the heaviest half, being the lowest; and if the pupa be again brought to the surface, so that the fluid is repelled from its disk, it remains suspended there without effort, as before. Just previously to the exclusion of the fly, the dry part of the thorax is seen to split in the middle. The air enters, and forms a brilliant stratum resembling quicksilver, between the body of the insect and its puparium; and the former pushing forth its head and forelegs, like the gnat, rests the latter upon the water, and in a few seconds extricates itself wholly from its envelope.

Before I close this letter, I must state a fact connected with the subject of it that deserves to be recorded. It is a general rule, that one pupa-case incloses only one insect; but Kleesius, a German entomologist, asserts that he had once two specimens of Gastropacha quercifolia produced from one pupa; which was large, being full two inches long, and one thick.

FOOTNOTES:

[562] In the Hemiptera the male Cocci (Reaum. iv. 32.) and Aleyrodes (Ibid. ii. 311.) belong to the second division.Return to passage

[563] The terms larva and pupa, applied to the insects of this subdivision, are perhaps not strictly proper.Return to passage

[564] The larvæ and pupæ of many of the homopterous section of Hemiptera differ often from the imago, not only in their fore-legs (PLATE XVI. FIG. 4.), but also in other respects. I have the larva of a Centrotus from Canada, given me by Dr. Bigsby, which has a long anal process or tail.Return to passage

[565] See above, p. 125--.Return to passage

[566] iii. 135.Return to passage

[567] The pupæ of Cassida, Imatidium, &c. seem to vary somewhat from this type, the upper part being neither membranous nor exhibiting distinctly the form of the inclosed imago.Return to passage

[568] The following arrangement of pupæ is perhaps in some respects better than that above given. But it is scarcely possible to propose one free from objections.Return to passage

I. Capable of eating and walking.

i. Like the perfect insect, except in proportion and number of parts.

1. Except in proportion (Lice, Poduræ, Mites, Spiders, Scorpions, &c).

2. Except in proportion and number (Centipedes, Millepedes).

ii. With rudiments of the organs of flight.

1. With oral organs resembling those of the perfect insect (Hemiptera).

2. With oral organs differing from those of the perfect insect (Libellula L., Ephemera L.).

II. Incapable of eating and walking.

i. Incomplete pupæ.

ii. Obtected.

iii. Coarctate.

Lamarck divides the pupæ of insects that undergo a metamorphosis into three kinds, which he names--Chrysalis, Mumia, and Nympha.

i. Chrysalis. Under this denomination he includes all inactive pupæ inclosed in an opaque puparium which entirely conceals them. These he further subdivides into two kinds.

1. Chrysalis signata. This term is synonymous with the Pupa obtecta of Linné, or the Chrysalis of Lepidoptera and some Diptera.

2. Chrysalis dolioloides. Equivalent to the Pupa coarctata Linn. peculiar to those Diptera that assume this state in the skin of the larva.

ii. Mumia. All inactive pupæ which are covered by a transparent skin, through which all the parts of the inclosed imago may be seen, subdivided also into two.

1. Mumia coarctata. Corresponding with the Pupa incompleta Linn., which includes the Coleoptera and most of the Hymenoptera.

2. Mumia pseudonympha, confined to the Pupa of Phryganea and some others. This might be named Pupa subincompleta.

iii. Nympha. Under this denomination are included all insects that undergo only a partial metamorphosis, and are active in their pupa state, corresponding with the Pupa semicompleta Linn. and also subsemicompleta MacLeay. See Anim. sans Vertebr. iii. 285--.

M. Latreille has started an ingenious idea on this subject with regard to these kinds of metamorphosis, which comprehends both larva and pupa under a distinct denomination: as thus--

1. Demilarve and Deminymph, synonymous with the Semicomplete Metamorphosis. 2. Larve and Nymph, answering to Incomplete Metamorphosis. 3. Caterpillar and Chrysalis, answering to Obtected Metamorphosis. 4. Vermilarve and Pupa, answering to Coarctate Metamorphosis. N. Dict. d'Hist. Nat. xvi. 272.

[569] N. Dict. d'Hist. Nat. vii. 57.Return to passage

[570] De Geer ii. 105.Return to passage

[571] Reaum. ii. 428--.Return to passage

[572] Swamm. Bibl. Nat. Engl. Tr. ii. 32. t. xli. f. 2. Comp. Reaum. iv. t. xxv. f. 1.Return to passage

[573] Ibid. i. 144.Return to passage

[574] Reaum. i. 355.Return to passage

[575] N. Dict. d'Hist. Nat. ubi sup. 59.Return to passage

[576] PLATE XVI. FIG. 14. N. Dict. d'Hist. Nat. vii. 59.Return to passage

[577] Ins. Surinam. t. xliv.Return to passage

[578] De Geer v. 47. t. ii. f. 29-31.Return to passage

[579] In the pupa of Hydrophilus piccus (Lesser L. t. ii. f. 13, 14), the arrangement of the parts is nearly the same, but the tarsi are not reflexed.Return to passage

[580] Ibid. f. 9, 10. De Geer ii. t. xxxii. f. 5. Reaum. v. t. xxxvi. f. 14.Return to passage

[581] Reaum. Ibid. t. ii. f. 9.Return to passage

[582] The legs of Tipula replicata L. are placed in a similar way. De Geer vi. t. xx. f. 12. l.Return to passage

[583] Rös t. 81.Return to passage

[584] Ibid. t. 95.Return to passage

[585] De Geer vi. 237. t. xiv. f. 8.Return to passage

[586] Reaum. v. t. ii. f. 7. The anal and ventral spines of Tipula replicata are also remarkable. De Geer vi. t. xx. f. 14.Return to passage

[587] De Geer Ibid. 377. t. xxiii. f. 8, 9. n. Reaum. v. 42. t. vi. f. 9. m n.Return to passage

[588] The caterpillar consists of twelve segments (Lyonnet t. i. f. 4, 5), excluding the head; on each of which, except the 2d, 3d, and 12th, there is a pair of spiracles. The chrysalis usually exhibits an analogy to this structure, though the first, second, and last pair of spiracles are more or less obsolete in most.Return to passage

[589] De Geer ii. 847. t. xxix. f. 7. a b.Return to passage

[590] Animaux sans Vertebres, iii. 287.Return to passage

[591] N. Dict. d'Hist. Nat. vii. 57.Return to passage

[592] Sepp ii. t. i. f. 4. t. ii. f. 4. t. iv. f. 5.Return to passage

[593] PLATE XVI. FIG. 12.Return to passage

[594] PLATE XVI. FIG. 10.Return to passage

[595] Ins. Surinam. t. lx. It is singular that the chrysalis of its congener, Morpho Teucer, which she figures t. xxiii., exhibits no such process. The larvæ also widely differ.Return to passage

[596] PLATE XVI. FIG. 11.Return to passage

[597] Sepp ii. t. iii. f. 5.Return to passage

[598] Sepp i. t. vii. f. 5.Return to passage

[599] De Insectis, ed. Lister. t. 1.Return to passage

[600] Ins. Surinam. t. liii.Return to passage

[601] Sepp i. t. ii. f. 6.Return to passage

[602] N. Dict. d'Hist. Nat. vii. 60.Return to passage

[603] Ibid. 57.Return to passage

[604] See above, VOL. I. p. 131.Return to passage

[605] Reaum. ii. 158. t. viii. f. 4, 5.Return to passage

[606] Lesser L. i. 160. note. t. ii. f. 19.Return to passage

[607] N. Dict. d'Hist. Nat. xxvi. 165. Reaum. i. 347. Rösel says this is present only in some individuals. I. ii. 47.Return to passage

[608] PLATE XVI. FIG. 13. a.Return to passage

[609] Ins. Surinam. t. iii.Return to passage

[610] De Geer ii. 433. t. viii. f. 4. t.Return to passage

[611] See above, VOL. II. p. 300.Return to passage

[612] This description was taken from a puparium in my own cabinet; it is similarly described by De Geer i. 490. t. vii. f. 2.Return to passage

[613] PLATE XXIII. FIG. 8, 9.Return to passage

[614] Kliemann Beitrage, 304.Return to passage

[615] See above, VOL. I. 464.Return to passage

[616] Von Scheven in Naturf. stk. xx. 64. t. ii. f. 4.Return to passage

[617] PLATE XVII. FIG. 2. Lesser L. t. ii. f. 26.Return to passage

[618] PLATE XVII. FIG. 1. Lesser L. t. ii. f. 24, 25.Return to passage

[619] Whether M. Meigen has separated this fly generically from others, I am not aware: in my catalogue it stands under the name of Tyrophaga.Return to passage

[620] Reaum. iii. 376. t. xxxi. f. 7.Return to passage

[621] Ibid. iv. 318. t. xxiii. f. 1-4. xxv. f. 1.Return to passage

[622] Ins. Surinam. t. xxix.Return to passage

[623] Ins. Surinam. t. xxxii. Lister imitated the gilding of Chrysalises by putting a small piece of a black gall in a strong decoction of nettles: this produced a scum, which when left on cup-paper, he says, will exquisitely gild it.--Ray's Letters, 87. 90.Return to passage

[624] Beitrage, 181.Return to passage

[625] Sepp. pt. ii. t. ii. f. 4.Return to passage

[626] Rösel. I. i. 61. ii. 5.Return to passage

[627] Reaum. i. 383.Return to passage

[628] Lister's Goedart. 122.Return to passage

[629] Reaum. ii. 10--.Return to passage

[630] Ibid. 24.Return to passage

[631] This is a legend of Virgil, of which an account is given in The Lay of the Last Minstrel, Note xv. 12mo ed. 1822, p. 257.Return to passage

[632] Haworth Lepidopt. Britann. i. 125. An instance is recorded in Scriba's Journal, in which a pupa was not disclosed until the fourth year. B. i. st. iii. 222. Pezold. 170.Return to passage

[633] Marsham in Linn. Trans. x. 402.Return to passage

[634] Meinecken found, that of several pupæ of Saturnia pavonia, some kept all winter in a room heated daily by a stove, and others in a cold chamber, some of both parcels appeared in March (none earlier), and some of both had not appeared in July, though evidently healthy. Naturf. viii. 143.Return to passage

[635] The exclusion of certain moths, &c. from the pupa is probably regulated by the time their eggs require to be hatched, and the appearance of the leaves that constitute their appropriate food.Return to passage

[636] Mr. Marsham makes a similar observation in Linn. Trans., ubi supr.Return to passage

[637] See above, p. 245.Return to passage

[638] The appearance of them sometimes continues to near the end of the month: it began on the 19th, when Reaumur observed them. vi. 480. 488.Return to passage

[639] Bibl. Nat. E. Transl. i. 103--.Return to passage

[640] Reaum. vi. 486.Return to passage

[641] Brahm. 423. 421.Return to passage

[642] Naturf. xxi. 75.Return to passage

[643] Reaum. ii. 423.Return to passage

[644] De Geer ii. 370. It is not certain, however, that De Geer did not, in this instance, mistake the winter habitation of a larva for a cocoon intended to shelter the future chrysalis; since Lyonnet informs us that they spin a habitation to pass the winter in. Traité Anatomique, &c. 9.Return to passage

[645] De Geer i. 490. t. vii. f. 3, 4.Return to passage

[646] Œuv. ii. 1.Return to passage

[647] De Geer v. 229.Return to passage

[648] VOL. II. 300--.Return to passage

[649] VOL. II. 298--.Return to passage

[650] I. iv. 101.Return to passage

[651] Reaum. vi. 407.Return to passage

[652] Haworth Lepidopt. Britann. i. 127.Return to passage

[653] De Geer ii. 566.Return to passage

[654] Reaum. iii. t. xlv. f. 12-14.Return to passage

[655] For this whole account, see Reaum. iv. Mem. viii.Return to passage

[656] Ibid. 472.Return to passage

[657] See above, p. 255--. and VOL. II. p. 301--.Return to passage

[658] Bonnet, Œuv. ii. 169.Return to passage

[659] Bonnet, Œuvr. ii. 207.Return to passage

[660] Rös. I. iv. 209. t. lxiii. ccxii.Return to passage

[661] See above, p. 217.Return to passage

[662] Bonnet, Œuvr. ii. 229.Return to passage

[663] De Geer ii. 477.Return to passage

[664] Sepp. iv. t. xi. f. 8.Return to passage

[665] PLATE XVII. FIG. 5. N.B. Sepp's figure represents the exterior funnel; and this, which exhibits the cocoon divided longitudinally, the interior one, or dome.Return to passage

[666] Rös. I. iv. 31.Return to passage

[667] Naturf. viii. 133.Return to passage

[668] De Bombyc. 29.Return to passage

[669] Reaum. i. 624.Return to passage

[670] Trans. of the Society of Arts, vii. 131.Return to passage

[671] Reaum. ubi supr.Return to passage

[672] ii. 359.Return to passage

[673] Linn. Trans. vii. 35.Return to passage

[674] Pezold. 171.Return to passage

[675] Lyonnet 16.Return to passage

[676] Some Notice of the Insect which destroys the Locust-trees, 70. This Memoir is in some American periodical work, of which I have not the title.Return to passage

[677] Huber Fourmis 82.Return to passage

[678] VOL. I. p. 467.Return to passage

[679] VOL. II. p. 264.Return to passage

[680] De Geer ii. 519.Return to passage

[681] Reaum. iv. 610--.Return to passage

[682] Ibid. v. 30--. t. v. f. 1-10. See above, p. 153--.Return to passage

Letter XXXII

STATES OF INSECTS.

IMAGO STATE.

When the insect has quitted the exuviæ of the pupa, it has attained the last stage of its existence. It is now termed an Imago, or perfect insect; and is capable of propagation.

Just after its exclusion, it is weak, soft, and languid: all its parts are covered with moisture; and, if a winged insect, its wings have so little the appearance, either in shape, size, or colour, which they are about to assume, that it might be taken for a mutilated abortion, rather than an animal in the most vigorous stage of life. If it be a beetle, its elytra, instead of covering the back of the abdomen, are folded over the breast: their substance is soft and leathery, and their white colour exhibits no traces of the several tints which are to adorn them. If the insect be a butterfly or a moth, the wings, instead of being of their subsequent amplitude, and variegated and painted with a variety of hues and markings, are in large species scarcely bigger than the little finger nail, falling over the sides of the trunk, and of a dull muddy colour, in which no distinct characters can be traced. If the excluded insect be a bee or a fly, its whole skin is white and looks fleshy, and quite unlike the coloured hairy crust which it will turn to in an hour or two; and the wings, instead of being a thin, transparent, expanded film, are contracted into a thick, opaque, wrinkled mass.

These symptoms of debility and imperfection, however, in most cases speedily vanish. The insect, fixing itself on the spoils of the pupa, or some other convenient neighbouring support, first stretches out one organ, and then another: the moisture of its skin evaporates, the texture becomes firm, the colours come forth in all their beauty; the hairs and scales assume their natural position; and the wings expanding, extend often to five or six times their former size--exhibiting, as if by magic, either the thin transparent membranes of the bee or fly, or the painted and scaly films of the butterfly or moth, or the coloured shells of the beetle. The proceedings here described I witnessed very recently with regard to a very interesting and beautiful butterfly, the only one of its description that Britain has yet been ascertained to produce--I mean Papilio Machaon. The pupa of this being brought to me by a friend early in May this year (1822), on the sixteenth of that month I had the pleasure to see it leave its puparium. With great care I placed it upon my arm, where it kept pacing about for the space of more than an hour; when all its parts appearing consolidated and developed, and the animal perfect in beauty, I secured it, though not without great reluctance, for my cabinet--it being the only living specimen of this fine fly I had ever seen. To observe how gradual, and yet how rapid, was the development of the parts and organs, and particularly of the wings, and the perfect coming forth of the colours and spots, as the sun gave vigour to it, was a most interesting spectacle. At first it was unable to elevate or even move its wings; but in proportion as the aërial or other fluid was forced by the motions of its trunk into their nervures, their numerous corrugations and folds gradually yielded to the action, till they had gained their greatest extent, and the film between all the nervures became tense. The ocelli, and spots and bars, which appeared at first as but germes or rudiments of what they were to be, grew with the growing wing, and shone forth upon its complete expansion in full magnitude and beauty.

To understand more clearly the cause of this rapid expansion and development of the wings, I have before explained to you that these organs, though often exceedingly thin, are always composed of two membranes, having most commonly a number of hollow vessels, miscalled nerves, running between them[683]. These tubes, which, after the French Entomologists, I would name nervures, contribute as well to the development of the wings, as to their subsequent tension. In the pupa, and commonly afterwards, the two membranes composing the organs in question do not touch each other's inner surface, as they afterwards do: there is consequently a space between them; and being moist, and corrugated into a vast number of folds like those of a fan, but transverse as well as longitudinal, and so minute as to be imperceptible to the naked eye, the wings appear much thicker than in the end. Now as soon as the insect is disclosed, a fluid enters the tubes, and being impelled into their minutest ramifications, necessarily expands their folds; for the nervures themselves are folded, and as they gradually extend in length with them, the moist membranes attached to them are also unfolded and extended. In proportion as this takes place, the expanding membranes approach each other, and at last, being dried by the action of the atmosphere, become one. To promote this motion of the fluid, seems the object of the agitations which the animal from time to time gives to its unexpanded wings. That a kind of circulation, or rather an injection of an aqueous fluid into these organs, actually takes place, may be ascertained by a very simple experiment. If you clip the wings of a butterfly during the process of expansion, you will see that the nervures are not only hollow, but that, however dry and empty they may subsequently be found, they at that time actually contain such a fluid[684]. Swammerdam, who appears to have been the first physiologist that paid attention to this subject, was of opinion that an aëriform as well as an aquiform fluid contributes to produce the effect we are considering. He had observed that, if a small portion be cut off from the wing of a bee, a fluid of the latter kind exuded from its vessels in the form of pellucid globules, becoming insensibly drops--which he concluded proved the action of the latter; and he noticed, also, that the wings were furnished with tracheæ, which were at that time distended by the injected air; whence he justly surmised, that the action of the air was also of great importance to produce the expansion of the wing[685]. And Jurine found that every nervure contains a trachea, which, proceeding from the interior of the trunk in a serpentine direction, follows all the ramification of the nervure, though it does not fill it[686]. Though Reaumur attributes the expansion of the wings chiefly to an aqueous fluid, yet he suspects that the air on some occasions contributed to it[687].

The wings of the other tribes of insects probably differ from the Lepidoptera in the manner in which they are folded. It should seem from Reaumur's description, that those of some flies, instead of the straight transverse folds of the former, have angular or zigzag folds[688]; which equally shorten the wing. Many Hymenoptera have wings without any nervures except the marginal. We may conjecture that these are more simply folded, so as to render their expansion more easy; but even in these wings there are often tracheæ, which appear as spurious nervures, and help to effect the purpose we are considering.

The operation of expanding their wings, in by far the larger number of insects, takes place gradually as described above; and, according to their size, is ended in five, ten, or fifteen minutes; in some butterflies half an hour, in some even an hour. A few species, such as Sphinx Œnotheræ F., require several hours, or even a day, for this operation; and, from the distance to which they creep before it has taken place, a considerable degree of motion seems requisite for causing the necessary impulse of the expanding fluids[689]. In a few genera, however, as the gnat, the gnat-like Tipulidæ, and the Ephemeræ, this process is so rapid and instantaneous, that the wings are scarcely disengaged from the wing-cases before they are fully expanded and fit for flying. These genera quit the pupa at the surface of the water, from which, after resting upon it for a few moments, they take flight: but this would evidently be impracticable, and immersion in the fluid, and consequent death, would result, were not the general rule in their case deviated from.

Some species of the last of these genera, Ephemera, are distinguished by another peculiarity, unparalleled, as far as is known, in the rest of the insect world. After being released from the puparium, and making use of their expanded wings for flight, often to a considerable distance, they have yet to undergo another metamorphosis. They fix themselves by their claws in a vertical position upon some object, and withdraw every part of the body, even the legs and wings, from a thin pellicle which has inclosed them, as a glove does the fingers; and so exactly do the exuviæ, which remain attached to the spot where the Ephemera disrobed itself, retain their former figure, that I have more than once at first sight mistaken them for the perfect insect. You can conceive without difficulty how the body, and even legs, can be withdrawn from their cases; but you must be puzzled to conjecture how the wings, which seem as thin, as much expanded, and as rigid as those of a fly, can admit of having any sheath stripped from them; much less how they can be withdrawn, as they are, through a small opening at the base of the sheath. The fact seems to be, that though the outer covering is rigid, the wing inclosed in it, notwithstanding it is sometimes more than twenty-four hours before the change ensues, is kept moist and pliable. In proportion, therefore, as the insect disengages itself from the anterior part of the skin, the interior or real wings become contracted by a number of plaits into a form nearly cylindrical, which readily admits of their being pulled through the opening lately mentioned; and as soon as the insect is released from its envelope, the plaits unfold, and the wing returns to its former shape and dimensions. Thus our little animal, having bid adieu to its shirt and drawers, becomes, but in a very harmless sense, a genuine descamisado and sansculotte. It does not seem improbable, that the pellicle we have been speaking of is analogous to that which, in addition to the outer skin, incloses the limbs of Lepidoptera, &c. in the pupa state, but which they cast at the same time with the puparium, and leave adhering to it[690].

The body of newly-disclosed insects commonly appears at first of its full size; but the aphidivorous flies (Syrphus F. &c.), and some others, in about a quarter of an hour after leaving the pupa become at least twice as large as they were at their first appearance: this apparent sudden growth, which is also noticed by Goedart, Reaumur found to depend upon the expansion of the previously compressed segments of the animal by means of the included air[691]. Both in this instance and in that of insects whose wings only require expansion, the size of the imago often so greatly exceeds that of the pupa, that we can scarcely believe our eyes that it should have been included in so contracted a space. The pupa of one of the beautiful lace-winged flies (Hemerobius Perla) is not so big as a small pea, yet the body of the fly is nearly half an inch long, and covers, when its wings and antennæ are expanded, a surface of an inch square[692].

When the development of the perfect insect is complete, and all its parts and organs have attained the requisite firmness and solidity[693], it immediately begins to exercise them in their intended functions; it walks, runs, or flies in search of food; or of the other sex of its own species, if it be a male, that it may fulfill the great end of its existence in this state--the propagation of its kind. Previously to thus launching into the wide world, or at least immediately afterwards, almost all insects discharge from their intestines some drops of an excrementitious fluid, often transparent, and sometimes red. I have before related to you the alarm that this last circumstance has now and then produced on the minds of the ignorant and superstitious[694]. Whether this excrement is produced indifferently both by males and females I cannot positively assert; but a circumstance related by Jurine affords some ground for a suspicion that it is peculiar to the latter. A specimen of a female of Lasiocampa Rubi, when killed emitted some of this fluid, which dropped upon the floor: this appeared to attract the males to the apartment in which it happened, and to the very spot--from whence it may be conjectured, that the scent of the fluid brought them there, and that the use of it is to bring the sexes together soon after exclusion from the pupa[695].

The colour, sculpture, and other peculiarities which distinguish insects in this state I shall consider at large in another letter, when I treat of their external parts and organs. Under the present head I shall confine myself to pointing out the characters by which the sexes of many species are distinguished from each other; as likewise the duration of their life in their perfect state; together with the circumstances on which this duration depends.

I. Sexual Distinctions. The first general rule that may be laid down under this section is,--That among insects, contrary to what mostly occurs in vertebrate animals, the size of the female is almost constantly larger than that of the male. Even in the larva and pupa states, a practised eye can judge, from their greater size, which individuals will become females. There are, however, some exceptions to this rule. Thus amongst the Coleoptera, the male Dynastidæ, remarkable for their horns, as you may see in D. Alocus, Antæus, Actæon, &c., as likewise those of Lucanus, are larger than the unarmed females[696]. In the Neuroptera the female Libellulidæ are sometimes sensibly smaller, and never larger, than their males[697]. In the Hymenoptera the male of the hive-bee, but more particularly that of Anthidium manicatum and other bees of that genus, is much more robust than the other sex[698]. In the Diptera, the same difference is observable in Syrphus Ribesii, and some other aphidivorous flies, and also in Scatophaga stercoraria[699]. And amongst the apterous tribes, we are informed by De Geer that the male of Argyroneta aquatica, which builds an aërial palace in the bosom of the waters[700], usually exceeds the female in bulk[701]. The reason of this rule seems in some degree connected with the office of the female as a mother, that sufficient space may be allowed for the vast number of eggs she is destined to produce; and it is when impregnation has taken place, and the eggs are ready for extrusion, that the difference is most sensible. In the majority of cases this sexual disproportion is not very considerable, but in some few it is enormous. Reaumur mentions a beetle, of which he intended to give the history, the male of which is so small compared with the female, that a bull not bigger than a sheep, or even a hare, set by the side of the largest cow, would aptly contrast with them. This little beetle, he says, has wings and elytra, while the giant female has no vestige of either, having the upper surface of its body naked and membranous[702]. The species to which this illustrious Naturalist here alludes, does not appear to have been ascertained. The female of many gall-insects (Cocci) is so large in comparison with the male, that the latter traverses her back as an ample area for a walk[703]. But this is nothing compared with the prodigious difference between the sexes of Termes fatale, and other species of white ants, whose males are often many thousand times less than the females, when the latter are distended with eggs[704]. Accidental differences in the size of the sexes sometimes arise: as when the female larva has, from any cause, been deprived of its proper supply of food, it will occasionally be less than the male. De Geer has stated a circumstance with respect to the Aphides that produce galls, that should be mentioned under this head--the first, or mother female, is larger than any of her progeny ever become[705].

The second observation that may be generally applied to the sexes of insects is, that, size excepted, there is a close resemblance between them in other respects. But to this rule the exceptions are very numerous, and so important that it is necessary to specify examples of each under distinct heads.

i. In some species the sexes are either partly or wholly of a different colour. Thus, in the order Coleoptera, the elytra of the male of Rhagium meridianum F. are testaceous, and those of the female black. Leptura rubra of Linné, with red elytra, is the female of his L. testacea, in which they are testaceous. Cantharis dermestoides of the same author is the other sex of his Meloe Marci; one of which is chiefly testaceous, and the other black: which seems to have so misled Linné, that he placed them in different genera. One more instance in this order, the female of Cicindela campestris, as was first observed to me by our friend Sheppard, has a black dot on each elytrum, not far from its base near the suture, which the male has not.

Amongst the Orthoptera, the male Locustæ F., as Professor Lichtenstein has informed us[706], have a fenestrated ocellus, which is not to be found in the other sex. I was once attending to the proceedings of a Hemipterous species, Pentatoma oleracea Latr., which I found in union: the paired insects had white spots, but another individual was standing by them, in which the spots were of a sanguine hue. I mention this by the way only--the spots in the prolific sexes being of the same colour: but might not the red spotted one be a neuter?

The sexes of many Lepidoptera likewise differ in their colour. I must single out a few from a great number of instances. The males of Lycæna Argus F. have the upper surface of their anterior wings of a dark blue, while in the female it is wholly brown. The wings of the former sex of Hypogymna dispar are gray, clouded with brown; but those of the latter are white, with black spots. In the brimstone butterfly (Colias Rhamni), which is one of the first that appear in the spring, the wings of the male are yellow--of the female whitish. In the common orange-tip (Pieris Cardamines F.), one sex has not the orange tip to the upper wings: and, to name no more, the male of Lycæna dispar, one of our rarest and most beautiful butterflies, has only a single black spot in the disk of its fulgid wings; while in the other sex, the primary pair have nine, and the secondary are black, with a transverse orange fascia near the posterior margin. But the most remarkable difference in this respect observable in the insects of the order in question, takes place in a tribe, of which only one species is certainly known to inhabit Britain--I mean the Papiliones Equites of Linné: what he has called his Trojani and Achivi in some instances have proved only different sexes of the same species. Mr. MacLeay's rich cabinet affords a singular instance confirming this assertion;--a specimen of a Papilio is divided longitudinally, the right hand side being male, and the left hand female. The former belongs to P. Polycaon, a Grecian, the latter to P. Laodocus, a Trojan. An instance of two Grecians thus united is recorded in the Encyclopédie Méthodique, as exhibited in a specimen preserved in the Museum of Natural History at Paris; which on the right hand side is P. Ulysses, on the left P. Diomedes[707].

In the Neuroptera, the Libellulidæ are remarkable for the differences of colour in the sexes. In the common Libellula depressa, which you may see hawking over every pool, the abdomen of the male is usually slate-colour, while that of his partner is yellow, but with darker side-spots. Reaumur, however, noticed some males that were of the same colour with the females[708]. Schelver observed, when he put the skins of Libellula depressa into water, that the colours common to both sexes were in the substance of the skin, and remained fixed; while those that were peculiar to one could be taken off with a hair-pencil, and coloured the water: which therefore were superficial, and, as it were, laid on[709]. The yellow males, therefore, that Reaumur observed, were probably such as had the superficial blue colour which distinguishes them washed off. In Calepteryx Virgo Leach, the former are of a lovely silky blue, and the latter green. In Agrions F. nature sports infinitely in the colours of the sexes.

In the order Hymenoptera there are often differences equally great; the sexes of many of the Ichneumons and Saw-flies are of quite different colours. The former tribe Linné has divided into sections, from the white annulus observable in the antennæ of some, and from the colour of their scutellum: but these are often merely sexual characters[710]. The male of Anthophora retusa Latr., a kind of wild bee, is wholly black, the female wholly gray, and of so very different an aspect that they were long regarded as distinct species; a mistake which has likewise occurred with regard to the sexes of Osmia cærulescens, another bee, of which the male has a bronzed and the female a violet abdomen[711]. The nose of male Andrenæ Latr. is often yellow, or white, as in A. hæmorrhoidalis--when that of the female is black[712]. The labrum also is often of a different colour in the sexes, as in Ceratina Latr.

In the Diptera, Aptera, Arachnida, &c., I am not aware of any striking difference in the colours of the sexes.

ii. The sexes of insects vary (but more rarely than in colour) in their sculpture also, and pubescence. Thus the elytra of the females of many of the larger water-beetles (Dytiscus) are deeply furrowed, while those of the males are quite smooth and level[713]. The thorax of the female in several species of Colymbetes of the same tribe, as C. Hybneri and transversalis, on each side has several tortuous impressed lines or scratches, like net-work, which are not to be discovered in the male. Hyphydrus gibbus Latr., which differs solely from H. ovalis (Dytiscus ovalis Illig.) in being thickly covered with minute impressed puncta, is, from the observation of the Rev. R. Sheppard, the other sex of this last, with which he has taken it coupled; and it is by no means improbable that Hydroporus picipes (Dytiscus punctatus Marsh.) and H. lineatus,--between which, as Gyllenhal has justly observed, the same difference only exists,--are in like manner sexual varieties. With respect to pubescence, I have not much to say. Another aquatic beetle, Acilius sulcatus Leach, has not only its elytra sulcated, but the furrows of these, and a transverse one of the thorax, are thickly set with hair; while the male is smooth, and quite naked. Particular care seems to have been taken by the Creator, that when all the above inhabitants of the water are paired, the male should be able to fix himself so firmly, by means of his remarkable anterior tarsi, (which I shall afterwards describe,) and these asperities, &c. in the upper surface of his mate, as not to be displaced by the fluctuations of that element, the reluctance of the coy female, or any other slighter cause.

In a moth called the ghost (Hepialus Humuli), the posterior tibia of the male is densely bearded, but not of the female[714].--Some Hymenoptera, as Ammophila Kirb. and Stigmus Jurine, have the upper lip of the male clothed with silver pile, while that of the female is not so ornamented. The legs of some bees are distinguished in the sexes by a difference in their clothing. That observable in those of the hive-bee has been before noticed[715]. In Andrena of Latreille[716] the posterior tibia of the female is covered externally with a dense brush of hairs, for collecting the pollen; and the posterior legs at their base have a curled lock of hair--which are not to be found in the male[717]. In Dasypoda, Melecta, Anthophora, Centris, Epicharis, &c. of the same author, the first joint of the tarsus of the female, and in Xylocopa almost the whole tarsus, is also similarly signalized from that of the other sex. In Bombus, as in the hive-bee, the posterior tibiæ of the females and neuters are furnished with a basket of hairs for carrying their pollen paste, which you will in vain look for in the male[718]. The latter, however, in some species of this tribe are distinguished from the former by the longer hairs of their legs, but not in the posterior ones. Thus, in Anthophora retusa the first joints of the intermediate tarsus are bearded internally with a thin fringe of long hairs, and the first externally with a triangular one of short ones at the apex: but what is most remarkable, the last or unguicular joint, which in almost every other bee is naked, is on both sides fringed with long hairs[719]. In that remarkable genus Acanthopus Illig., of which the male only is known, the first and last joint of the intermediate tarsus have a dense external brush of stiff hairs, which probably is also a sexual character[720]. Another sexual kind of clothing is exhibited by the females of those bees that have their labrum or upper-lip inflexed (Megachile Latr.)[721]. Their abdomen is covered underneath with a brush of stiff hairs, involved in which they carry the pollen they collect. In the males of some of this tribe, as of M. Willughbiella, the first four joints of the anterior tarsus on their inner side have a long dense fringe of incurved hairs[722]: a circumstance also to be found in the same sex of Xylocopa latipes, in which the claw-joint also is bearded[723]. In Andrena Latr. the last dorsal segment of the abdomen of the same sex is fringed, while that of the male is naked[724]. In the humble-bees (Bombus), the mandibles of the male are bearded with curled hairs, while those of the females and neuters are without them. Some bees, as Andrena and Halictus Latr., have the anus of the female bearded, and that of the male naked: in some Bombyces the reverse takes place.

iii. With regard to the general shape of their body, the male and female usually resemble each other: but there are some exceptions to this rule. The male of the hive-bee is much thicker and more clumsy than either the female or the worker; but in Halictus Latr. the males are nearly cylindrical in shape, and very narrow; while the other sex are oblong or ovate, especially their abdomen: and in Andrena Latr. the former are much slenderer than the females, and of a more lanceolate shape. But a still more striking difference in this respect between the sexes is exhibited by some species of the genus Ptinus F., in which the male is long and slender, and the female short and thick. This, in more than one instance, has occasioned them to be mistaken for distinct insects: thus, P. Lichenum and P. similis, P. ovatus and P. testaceus, of Mr. Marsham, are mere sexual varieties. But the most entire abalienation of shape at present known, is that which distinguishes the male from the female Coccus; these are so completely dissimilar as scarcely to have any part in common. In Bombyx vestita F., and others of the same family, while the males are of the ordinary conformation of the order, the females are without even the slightest rudiments of wings; they have no antennæ, the legs are extremely short, not longer than those of the caterpillar; and the body is entirely destitute of scales, so that they altogether assume the exact appearance of hexapod larvæ[725]. A conformation nearly similar takes place in the female of Tinea Lichenella; but in this the feet are longer, and the anus is furnished with a long retractile ovipositor[726].

iv. In many cases, the structure of particular parts and organs of the body differs in the sexes. As the facts connected with this part of our present subject are extremely numerous and various, it will be convenient to subdivide it, and consider the sexual characters that distinguish--the Head, Trunk, and Abdomen of insects, and their several appendages.

1. The Head. This part in some females is considerably larger than it is in the male. This is the case with the ants, and several other Hymenoptera; while in some Andrenæ, as A. hæmorrhoidalis, and Staphylinidæ, as St. olens, that of the male is the largest. But in none is the difference more conspicuous than in the stag-beetle (Lucanus); in which genus the male not only exceeds the female in the length of his mandibles, but also greatly in the size and dimensions of his head. In the Apion genus, the rostrum of the female is generally longer and slenderer than that of her mate; and in Brentus, the rostrum of one sex (probably the male) is long and filiform, while in the other it is thick and short. This is particularly visible in B. dispar and maxillosus[727], &c.

One of the most striking distinctions of the males in this part of their body, are those threatening horns, usually hollow, with which the heads of many of the male lamellicorn insects and some others are armed, and which give them some resemblance to many of the larger quadrupeds. Many are unicorns, and have their head armed with only a single horn; which in some, as in Oryctes Illig., Dynastes Endymion[728], &c. is very short; in others, very long, as in Dynastes Enema, Pan, Elephas[729]. In one, again, it is thick and robust; as in the clumsy Dynastes Actæon[730]: in another very slender, as in Onthophagus spinifer[731]. With respect to its direction in Elephastomus proboscideus MacLeay, it is horizontal[732] and straight; in Phaleria cornuta horizontal and broken, or the apex turning outwards and forming an angle with the base[733]; in Dynastes Hercules horizontal, and recurved at the apex[734]; in D. Actæon, Elephas, and Typhon, recurving from the base. In Geotrupes dispar it is recurved, so that its point exactly coincides with that of the porrected thoracic horn, with which it forms a kind of forceps[735]. In Copris lunaris F. and Diaperis horrida, the horn is nearly upright[736]. In Onthophagus Xiphias it is dilated at the base, and reclining upon the thorax; and at the apex attenuated, and bending forwards, or nodding. In Passalus cornutus it rises a little, and then bends wholly forwards. In Dynastes Milon, a most remarkable beetle, it slopes backwards in a waving line[737]; and in Onthophagus spinifer it is recurved and reclining.--In speaking of the direction of the horn, you must recollect that it will vary in proportion as the head varies from a horizontal position: so that an upright horn will become inclined or reclined, as the head bends forwards or backwards; but I speak of it as it appears when the head is horizontal. Again, it varies in its teeth or branches. In Dynastes Hercules it is armed with several teeth. In D. Elephas and Actæon it has only one large one at its upper base[738]. In D. Milon it is serrated above. In D. Alcides, Tityus, Ægeon, Copris lunaris, &c. the horn is unarmed and simple at the apex. In D. Oromedon, Gedeon, Enema, Actæon and congeners, it is bifid. In some the horn is at first a broad lamina or ridge, which terminates in two branches, as in Onthophagus Vacca. In this the branches are straight; but in another undescribed species in my cabinet (O. Aries Kirby, MS.) they are first bent inwards, and then at the apex a little recurved: and in D. dichotomus it is divided into two short branches, each of which is bifid[739]. Other males emulate the bull, the he-goat, or the stag, in having a pair of horns on their head. In Onthophagus Taurus, these arms in their curvature exactly resemble those of the first of these animals[740]. In Goliathus pulverulentus, the straight, robust, diverging, sharp horns are not unlike those of some of the goat or gazel tribe. I have a beautiful little specimen in my cabinet, (I believe collected by Mr. Abbott of Georgia,) in which the horns have a lateral tooth, or short branch, like those of a stag; and which I have therefore named O. cervicornis. In O. Vacca, Camelus, &c. the horns are very short, and nearly perpendicular. In the male of Copris Midas, the two longer perpendicular horns have a deep cavity between them, which, together with its black colour, give it a most demoniac aspect; so that you would think it more aptly representative of a Beelzebub or Beelzebul than a Midas[741], or than Phanæus Beelzebul MacL. A similar cavity is between the occipital horns of Diaperis hæmorrhoidalis Payk. Some species of Rynchænus, as R. Taurus, have a pair of long horns upon the rostrum of the male, the rudiments only of which are to be traced in the female[742]. Other species go beyond any known quadrupeds in the number of horns that arm their heads. Thus Ditomus calydonius Bonelli, belonging to Carabus L., has three equal horns[743]. The same number distinguishes Onthophagus Bonasus; but the intermediate one is very short. In Goliathus Polyphemus the middle horn, on the contrary, is much longer and thicker than the lateral ones, and forked at the apex; so that it looks as if it had four of these weapons[744]. A little Diaperis (D. viridipennis F.), a native of Carolina, has four horns upon the head of the male; namely, two long ones on the occiput, and two short dentiform ones on the nose. In a species nearly related to this, sent me by Professor Peck from New England, there is a cavity between the two occipital horns. The same number distinguishes Onthophagus quadricornis (Copris F.). The situation also of the horns varies: In some it is in the middle of the head, as Oryctes nasicornis, Copris lunaris, &c.: in others, as in Onthophagus nuchicornis, Xiphias, &c. it is a process of the occiput or hind-head; and in O. Oryx F. the two horns proceed from the anterior part of the head. In the other sex, in insects the head of whose males is armed with horns, they are usually replaced by mere tubercles, or very short elevations, as you may see in the female of Copris lunaris; or by transverse ridges, as in the Onthophagi: or else the head is without arms, and quite smooth, as in Diaperis, Phaleria, &c. What may be the use of these extraordinary appendages, as well as those on the thorax, and in some cases on the abdomen, (which I shall mention afterwards), to the males, has not yet been ascertained. Whether the individuals of this sex are more exposed to the attack of birds and other enemies, in consequence of being more on the wing than the females, and are therefore thus provided with numerous projecting points for defence, is a question worth considering[745]. It is the only probable conjecture on the cui bono of these arms that I can at present make. Under this head I ought to notice the remarkable membranous process of an obovate shape, which like an umbrella covers the head of Acheta umbraculata F.[746] Whether the sharp curved horns which arm this part in another Acheta figured by Stoll[747], in an incumbent posture, with their point towards the mouth, are a sexual distinction, we are not informed,--probably they are.

The organs of the head also present many sexual distinctions. The upper lip (labrum) in Halictus Latr., a tribe of wild bees, in the female is furnished with an inflexed appendage, which is not discoverable in that of the male[748]; and the shape of this lip in Sphecodes Latr. differs in the sexes[749]. Perhaps the horn or tubercle observable on this part of some female Nomadæ F.[750] may be wanting in the male.

The under-lip (labium)--taken in a restricted sense for that central part from which emerge the labial palpi, and which is often considered as the mentum,--does not offer any striking variations in the sexes. One, however, is of importance, as it helps to prove which are the true female Lucani. In the male the labium is emarginate, in the female it is intire. This may be seen both in L. Cervus and femoratus, and probably in other species. The sculpture also is different, the lip being smooth in the former and covered with excavated puncta in the latter. The tongue (lingua or ligula) of the sexes is usually the same; except in the hive-bee, in which that of the neuters is longer than that of the male and female.

The upper-jaws (mandibulæ), however, often afford striking sexual characters. The enormous protended ones of the common stag-beetle (Lucanus Cervus) attract the attention of the most incurious observer; and these are now generally allowed to be of this description. Geoffroy and Mr. Marsham, indeed, have asserted that they have taken in coitu those with long mandibles: but as these males are pugnacious, and attack each other with great fury, as Mr. Sheppard informs me, it is not improbable that these gentlemen may have mistaken a battle for an amour: since not only have those with long mandibles been often taken united with those that have short ones[751], but the same difference obtains in the sexes of other species. This is particularly observable in Lucanus femoratus, of which I received from Brazil many specimens agreeing in every respect except in this, that one had short and the other very long mandibles. These organs vary in different specimens, as to the number of their teeth and branches. They are singularly robust in L. Alces[752]; but in none more threatening than in L. Elephas[753], in which they curve outwards and downwards. In Mr. W. MacLeay's genus Pholidotus, they are almost parallel to each other, and curve downwards; in Lucanus nebulosus Kirby, they assume a contrary direction[754]; as they do likewise in Lamprima Latr.[755] In Lucanus Capreolus the points close over each other[756]. In Lethrus F. in the female, but not the male, the mandible is armed below with a long incurved horn. In Lucanus serricornis they form a complete forceps[757]. In Siagonium quadricorne Kirby[758] the mandible is furnished at its base with an exterior horn, which is probably a sexual distinction. The male of Synagris cornuta, a kind of wasp, is still more conspicuous in this respect; for from the upper side of the base of its straight slender mandibles proceed a pair of crooked, decurved, tortuous, sharp horns, not only longer than the mandible, but than the head itself[759]. Many sexual differences are observable in the mandibles of the various tribes of bees (Anthophila Latr.). Thus, in Colletes Latr. the male mandible is more distinctly bidentate at the apex than the female[760]: in Sphecodes Latr. and others, the reverse of this takes place[761]. Where these organs in both sexes are toothed at the apex, they often vary in the number of teeth. Thus, the female of Megachile centuncularis Latr. has four teeth at the apex of its mandible, while the male has only two[762]. In M. Willughbiella, though the mandibles of both sexes have four teeth, yet those of the male are sharp, and the two external ones the longest; while those of his mate are obtuse, and all nearly equal in length[763]. In Anthidium manicatum Latr., the former has only three teeth, while the latter has five[764]. The differences in this respect in the hive-bee have been before noticed[765]; those of the humble-bees (Bombus Latr.) are strikingly distinguished from each other; the female mandible being very stout and wide, constricted in the middle, and furrowed on its outer surface; and the male, on the contrary, very slender at the apex, dilated at the base, and without furrows[766].

Of all the organs of the head, none seem so little subject to sexual variation as the under-jaws (maxillæ)[767]. I can bring forward only one striking instance of it, and some degree of doubt rests even upon that. In the genus Nemognatha of Illiger, the maxillæ of the male are elongated, narrow, setiform, and often involute or spiral, like those of a bee or a butterfly. But that this is peculiar to the males is at present only surmised[768]. I possess several species of the genus, all of which are distinguished by long maxillæ; though in some they are as long as the body, and in others scarcely half that length. Gnathium Kirby is similarly characterized[769].

The maxillary palpi occasionally differ in the sexes. In Cerocoma those of the female are filiform, while the two intermediate joints of those of the other sex are much thicker than the first and the last[770]. In Hylæcetus and Lymexylon, those of the male are still more remarkable: they are pendent, the last joint very large, and laciniated so as to form a tuft[771]. The female ones grow gradually larger towards the end, but are not at all divided there[772]. The palpi of male spiders are of a very different structure from those of the other sex, terminating in a very complex incrassated piece, which has been supposed to contain the organ of generation; but this, according to Treviranus, is a mistaken idea--that organ being, as usual, to be found in the abdomen[773]. In the common gnat the palpi of the male are as long as the proboscis, consist of five joints, and at the end are tufted with hairs; while those of the female are scarcely one-fourth of its length, have only three joints, and are not tufted. Whether the labial palpi in any genus differ in the sexes, I cannot affirm with certainty: I have not, however, observed any such variation in them.

I shall next mention some organs of the head, in which the difference between the sexes is often very striking and peculiar. You will readily conjecture that I am speaking of the antennæ. And here the advantage seems wholly on the side of the males: since in them these wonderful instruments of unknown sensations are not only more complex, but usually more elegant, than those of the other sex. You will pardon me, therefore, if I enlarge a little more than ordinary upon a subject so full of interest, and say something upon the differences observable between the sexes--in the shape, magnitude, and length, number of articulations, ramification and plumage, and individual joints of their antennæ.

With regard to their shape, variations are sometimes observable between the antennæ of the sexes; but this principally occurs in the Hymenoptera order. For instance, those of Chelostoma maxillosa, a small bee that deposits its eggs in little holes in posts and rails, are clavate in the female and filiform in the male[774]--a circumstance that distinguishes in some degree those of Sphecodes, Halictus, and Andrena of Latreille, three other genera of wild-bees[775]. In Dinetus Jur. the male antennæ are moniliform at the base, and filiform at the apex; the female, on the contrary, are entirely filiform[776].

The antennæ of the sexes also sometimes differ in magnitude and length. This is the case in the three genera of wild bees just mentioned; those of the female being thicker than those of the male, while these last are longer than the former. But in this tribe the males of the Fabrician genus Eucera are most remarkable for their long antennæ[777]. With regard to the different length of these organs in the sexes, no insects are more distinguished than some species of the capricorn-beetles (Cerambyx L.). In Lamia Sutor the male antennæ are twice the length of the female; and in another Brazilian species in my cabinet, related to L. annulata (Stenocorus F.), they are thrice their length. Some of the Anthribi F. approach the Cerambycidæ, not only in some other characters, but also in this circumstance:--thus the antennæ of A. albinus, a native of Britain, are vastly longer in the male than in the female; and in A. cinereus (Macrocephalus Oliv.)[778], which I suspect to be of the former sex, they are as long nearly as is usual in the tribe just named, called in France capricorn-beetles.

I may here observe, that sometimes in the sexes a difference is also to be found in the direction or flexure of their antennæ. Thus in Scolia F., Pepsis F. &c., in the males the antennæ are nearly straight, but in the females convolute or subspiral. The reverse of this takes place in Epipone spinipes, a kind of wasp, and its affinities; and Systropha Illig., a kind of bee: for in these the male antenna is convolute at the apex[779], and the female straight. In the various tribes of bees (Anthophila Latr.), these organs in the latter are what is denominated broken, the main body of the antenna forming an angle with the first joints: but in the former this does not take place.

The antennas of the sexes do not always agree in the number of joints. In the bees, and many other Hymenoptera, the male has one more joint than the female; as is the case also in Œdemera notata (Cantharis acuta Marsh.). In Pteronus Laricis, a kind of saw-fly, the latter has only sixteen joints in its antennæ, while the former has twenty-four[780]. In Rhipicera marginata, a beetle, the beautiful antennæ of the male consist of thirty-two joints, while the female has no more than eleven! In Chelonus Jur. the male, on the contrary, has the smallest number of joints, namely sixteen; while the female has twenty-five[781].

In nothing do the sexes differ more materially than in the ramification of these organs, and their plumage. By attending to this, you may often detect the sexes in an instant; since the antennæ of the males in numerous instances are much more complex than those of the females. For what end the Creator has so distinguished them is not quite clear; but most probably this complex structure is for the purpose of receiving from the atmosphere information of the station of the female. A tendency to branching will be found in the antennæ of some males, in tribes where these organs are usually perfectly simple in both sexes. Thus, in the male of Chelostoma maxillosa,--mistaken for another species by Linné, which he names Apis florisomnis,--the intermediate joints on their inner side project into an angle[782]; and those of the same sex of the common hornet, by means of a central sinus, have two obtuse teeth on each. With regard to more direct ramifications, some male antennæ terminate in a fork, or two branches. This is the case with Hylotoma furcata Latr., a saw-fly[783]; and the peacock-louse (Nirmus Pavonis Herm.)[784]. Others, again, have three lateral branches, as in Eulophus Geoffr. a little parasite, the male antennæ of which send forth a hairy external and rather long branch, from the base of the fourth, fifth, and sixth joints[785]. In Elater flabellicornis L., the eight last joints are flabellate, or elongated and flat, resembling the sticks of a fan in the male[786]; in the female they are shorter, and more properly may take their denomination from the teeth of a comb. In Lampyris Latreillii Kirby, the antennæ of the former are flabellate on both sides, while those of the latter are little more than serrate[787]. These organs are extremely beautiful in the males of the Rhipiceræ of Latreille. In R. marginata K. they consist of thirty-two joints, from thirty of which issues a branch, the first very short, but the rest gradually increasing in length as they approach the middle of the antenna; then gradually decreasing to the end, so as to represent an expanded fan[788]. But in none are they altogether so remarkable as in those moths that Linné denominates Bombyces Attaci, and some others. In these, in the males, these organs in their contour are lanceolate, and every joint is furnished with a couple of parallel equal branches on each side[789]. In the females these branches are shorter on the whole, and alternately one long and one short; but in some, as Saturnia Pavonia, there is only one short branch or tooth on each joint in this sex[790]. In Bombyx regalis &c. only the first part of the antenna is so branched; and those of the female are setaceous and without branches. In B. versicolor, &c. there is only one branch from each side on every joint; those of the female being much shorter than those of the male. The latter sex of Pteronus Laricis Jur., a saw-fly, afford an example of a different structure, the antennæ on one side sending forth a branch from every joint but the two first; but on the other side, the nine or ten last joints also are without a branch. The female antenna is serrated[791]. In another of this tribe, Pterygopterus cinctus Klug, the male antenna resembles a single-toothed comb, being branched only on one side: that of the female, like the former instance, is serrated[792]. Whether the remarkable antennæ that distinguish the known individuals of the genus Phengodes (Lampyris plumosa F.) is a sexual character has not been ascertained; but it is not improbable that it may be, as in other Lampyridæ. A pair of delicate flexile and almost convolute plumose branches proceeds from the apex of each joint except the basal ones, which have something the air of cirri, and give a more than usual degree of lightness and elegance to these organs[793]. Other antennæ, especially in the Diptera order, assume an appearance of plumes--not from the branches that proceed from them, but from the fine long hairs that beset and adorn them. These are universally indications of the male sex, those of the females being generally comparatively naked. If you take the common gnat, you will find that the antennæ of one individual are thickly fringed on each side, and tufted at the end with fine long hairs, while in the other only four or five placed at intervals in a whorl are to be perceived[794]. In Chironomus Meig., a kind of Tipula L., resembling a gnat, the male antennæ are beset on all sides with the finest hairs, and resemble a beautiful plume[795], while the females to the unarmed eye appear naked. Even in some Hymenoptera, the antennæ of the males are thus feathered, in a less degree: for instance, in Hylotoma Latr.[796] Whether the tufts and fringes which ornament, in a remarkable manner, the antennæ of many Cerambycidæ[797], are sexual characters, is not certainly known.

We are now to consider other sexual differences in these organs, resulting from the size or configuration of one or more individual joints. To begin with the first joint, or scapus. In many of the Hymenoptera, particularly the Anthophila Latr., this is elongated, and the remaining joints form an angle with it in the females: while in the other sex it is much shorter, and in the same line with the rest of the antennæ; and in Hylæus dilatatus (Melitta dilatata Kirby) the first joint in the male is dilated and shaped something like a patella[798]. In Malachius bipustulatus, &c. the sex just mentioned is peculiarly distinguished by a white excrescence on the first four joints of the organs in question, most conspicuous in the second and fourth. The antennæ of male Cerocomæ are not very different[799]. Mr. Marsham has described a little Haltica under the name of Chrysomela nodicornis, from a peculiarity of the same sex not to be found in the other. The fourth joint is very large and obtriangular; in the female it is merely longer than the rest. In H. Brassicæ and quadripustulata the fifth joint is larger and longer than all but the first in the male, in their females it is only longer. In some moths (Herminia Latr., Crambus F.) there is also a knot in the middle of the male antennæ[800]. In Noterus, a water-beetle, the six intermediate joints are thicker than the rest, beginning from the fourth, and the last but one ends internally in a truncated tooth. The fifth and two following joints in the male antennæ of Meloe are larger than the rest, which distinguishes them, as well as a remarkable bend observable at that part[801].

Variations of the kind we are considering are also observable in the clava, or knob, in which antennæ often terminate. You have doubtless observed that the lamellated clava of the antennæ of the common cockchafer is much longer and more conspicuous in some individuals than in others--the long clava belongs to the male[802]. In another species, M. Fullo, that of this sex is nine or ten times the length of that of the other. In Colymbetes serricornis, a water-beetle, the male has a serrated clava of four joints. In Dorcatoma dresdensis[803], and also Enoplium damicorne, two beetles, it is nearly branched in the male, but much less so in the female. In a little destructive beetle, common in our houses (Attagenus Pellio), in the latter it is very short, but in the former it is very long, and nearly formed by a single joint. In Eurhinus Kirby, a New Holland genus of the weevil-tribe, in the male the last joint, also, is much longer than it is in the female[804]. These examples will give you some idea of the principal variations that take place in the antennæ of the sexes, and of the wonderful diversity of forms in this respect to which mere sexuality gives rise amongst insects.

In the eyes, or stemmata, this diversity is less remarkable. Latreille has described two ants, Formica contracta and coeca, in the neuter of which he could discover no eyes[805]: in the former, the female, however, had large ones. The male he appears not to have known, but it probably was not destitute of these organs; of the latter he was acquainted only with the workers. The neuter of Myrmica rubra, another ant, has no ocelli or stemmata, although the male and female are provided with them[806]. They are discoverable only in the former sex of that singular insect related to the ants, Mutilla europæa. Other insects differ in the size of the eyes of their sexes. In the hive-bee, and some Ephemeræ, the eyes of the drone or male are much larger than those of the worker and female, and also meet at the vertex, having their stemmata below the conflux; whereas in these latter they are widely distant[807]. In Stratyomis, Tabanus, and many other two-winged flies, the male eyes meet at some point below the stemmata, and above the antennæ. In the former they touch more at an angle; for the vertex forming a narrow isosceles triangle, and for the anterior part of the face one nearly equilateral: while those of the female are separated by a considerable interval. In Heptatoma and Hæmatopota in that sex, a similar interval obtains; while in the other, after forming a minute short triangle, they unite for a considerable space, and then diverging, form the face. This is also the case in Tabanus; but in the female, the space that intervenes between the posterior part of the eyes is much narrower than in these two cognate genera of the horse-flies. In some others of this order, as Musca Latr., the eyes of the male do not touch, but approach posteriorly much nearer to each other than those of the other sex. In a few instances the sexes vary even in the number of their eyes, as well as the size. This occurs in some species of Ephemera L. (E. diptera, &c.), in which the male, besides the common lateral ones, has two large and striking intermediate eyes, that sit upon vertical pillars or footstalks[808].

2. The Trunk. The thorax of many coleopterous males, especially of the Dynastidæ and Copridæ amongst the petalocerous tribes, exhibits very striking differences from that of the female. In many Lucani the lateral angle is more prominent. In Anthia it is bilobed posteriorly, while in the last-mentioned sex it is entire[809]. In Phanæus carnifex MacLeay (Copris F.) it is elevated into a plane triangular space, with the vertex of the triangle pointing to the head; but in the female it is convex, with an anterior abbreviated transverse ridge[810].

In a large proportion terrific horns, often hollow, like those of the head lately noticed, arm the thorax of the male, of which you will usually only discover the rudiments in the other sex. In the first place, some are unicorns, or armed only with a single thoracic horn, which frequently, in conjunction with the thorax itself, not a little resembles a tunnel reversed: of this description are Dynastes Hercules, Tityus, Gedeon, Enema, &c.[811] In the three first this horn is porrected, or nearly in the same line with the body; but in the last, and D. Pan, it forms an angle with it; and in D. Ægeon it is nearly vertical[812]. In D. Hercules it is very long; in D. Alcides[813] and Tityus very short; in the two last, and in Oxytelus tricornis which is similarly armed, it is undivided at the apex; but in D. Gedeon, Pan, bilobus, &c.[814] it is bifid or bilobed. It is usually rather slender, but in D. Chorinæus[815] and bilobus, it is very stout and wide. In D. claviger it is hastate at the apex[816]. In D. hastatus it is short and truncated[817]. Others, again, have two thoracic horns. In Copris nemestrinus these are discoidal, diverging, and inclining forwards[818]. In Phanæus floriger[819] they are lateral, triangular, and incline towards each other, with, as it were, a deep basin between them. In P. splendidulus they sink into two longitudinal ridges, most elevated posteriorly, with an intervening valley[820]. In P. bellicosus they are posterior, compressed, truncated, and emarginate at the apex, and include a basin[821]. In Copris Sabæus they are merely two acute prominences[822].--Three horns distinguish the thorax of many. In D. Aloeus[823] and its affinities, they are arranged in a triangle, whose vertex is towards the head. In D. Antæus[824] these horns are nearly equal in length, and undivided at the apex. In D. Titanus[825] the anterior horn is longer than the rest, and bifid at the apex; in D. Atlas and Endymion[826], both of which have a horn on the head, it is much shorter. In others, as in Megasoma Kirby, the vertex of the triangle is towards the anus. In M. Typhon[827] it is longer than the anterior ones, and bifid at the apex; in M. lanigerum they are equal in length[828]. In M. Elephas and Actæon[829] it is merely an elevation of the thorax; in the last almost obsolete. In Geotrupes Typhæus, common on our heaths, the anterior of this part is armed by three horizontal horns, the intermediate one being the shortest[830]. Copris lunaris also, another of our own beetles, has three short posterior thoracic horns, two lateral and triangular ones, and a transverse intermediate elevation, with a notch in the middle[831]. In Dynastes Neptunus the horns are porrected, the middle one being very long, and the lateral ones short[832]. In D. Geryon the point of the lateral horns is towards the anus, and the base of the intermediate one covers the scutellum[833]. Others have four of these singular arms: this is the case with one of our rarest beetles, Bolbocerus mobilicornis K., which has four dentiform horns, the intermediate pair being the shortest, arranged in a transverse line on the anterior part of the thorax[834]. In B. quadridens these are merely teeth. In Phanæus Faunus[835] it has two lateral, elongated, compressed, truncate, horizontal horns, and two intermediate teeth. Dynastes Milon has a still greater number of horns on the thorax of the male, there being two lateral anterior ones and three posterior ones--the intermediate being the longest[836]; and Copris Antenor Fabricius and Olivier describe as having a many-toothed thorax; and from the figure of the latter[837], the male appears to have seven prominences.

But the males of insects are not only occasionally distinguished by these dorsal arms--in a few instances they are also furnished with pectoral ones. The illustrious traveller Humboldt found in South America a species of weevil (Cryptorhynchus Spiculator Humb.), the breast of which was armed with a pair of long projecting horns; and I possess both sexes of four species, three at least from Brazil, that exhibit in one individual the same character. One, concerning the country of which I am uncertain, recedes somewhat from the type of form of the rest, and comes very near that of Rynchænus Strix F.[838] In the individual which I take to be C. Spiculator, the pectoral horns are very long, curving upwards at the apex, and nearly in a horizontal position; while in the three others they are much shorter, and inclined towards the horizon. The males of some species of Rynchites, as R. Bacchus and Populi[839], are also armed with a pair of lateral horns or spines, which may be termed pectoral rather than dorsal.

I shall now advert to the sexual characters that are to be found in the instruments of motion attached to the trunk--beginning with those for flight. In the female of the common glow-worm (Lampyris noctiluca) not the slightest vestige of elytra or wings is visible, and it resembles a larva rather than a perfect insect; yet its mate is a true beetle furnished with both. The same circumstance distinguishes the female cockroach (Blatta) and is more universally prevalent in that genus than in Lampyris, in which a large number of females have both elytra and wings. The males of Bombyx antiqua and Gonostigma, and of many other moths, have wings of the usual ample dimensions, while those of their females are merely rudiments. This is the case, also, with some of the Ichneumonidæ[840]. In the tribes of Ants, Termites, &c. the neuters or workers are without wings. Amongst the plant-lice (Aphides) there are individuals of both sexes, some of which have wings, and others not[841]. Amongst the Coleoptera, the female of Tenebrio Molitor, the common meal-worm, has elytra and no wings; while the male has both[842].--Sometimes these organs vary in size in the sexes: thus in Aradus Betulæ F., a kind of bug, the hemelytra and wings are narrower and shorter in the female than in the male[843]. In the genus Blaps F., the mucro that arms the apex of each elytrum is longer in the former sex than in the latter. In Ateuchus gibbosus F., a dung-beetle, the elytra have a basal gibbosity near the suture in one sex that does not obtain in the other. In the Orthoptera order, the sexes are often to be known, almost at first sight, by a difference in the veining and areolets of the wings; but upon this I enlarged so fully when I treated of the sounds produced by insects, that it is not necessary to repeat what I have said; which observation also applies to the drums which distinguish the male Cicadæ[844]. The wings of some butterflies, and of most moths and hawkmoths (Sphinx L.), are furnished with a singular apparatus for keeping them steady, and the under-wing from passing over the upper in flight. This appears to have been first noticed by Moses Harris, and was afterwards more fully explained by M. Esprit Giorna[845]. From the base of the under-wing proceeds a strong bristle, received by an annulus or socket, which springing between the two principal nervures of the upper-wing terminates in the disk of the wing: in this annulus the bristle moves to and fro, and prevents the displacement of the under-wing. This apparatus is perfect only in the males, which alone have occasion for long flights; the females, though they have often several bristles, having no annulus[846].

The other instruments of motion, the legs, also differ in the sexes. In some instances they are disproportionably long. This is particularly the case with the anterior pair of some beetles, as Macropus longimanus, Scarabæus longimanus L., in which they are so long as to make the males of these individuals rather inconvenient in a cabinet. Amongst British beetles Clytra longimana and Curculio longimanus Marsh. are also remarkable in this respect. In some other males the middle pair are the longest; as in Anthophora retusa Latr., a kind of wild-bee[847]. There are two known instances of remarkably long posterior legs in the Capricorn tribe, which I suspect belong to the present head. One is Saperda hirtipes Oliv.[848], in which the hind-legs are longer than the whole body, and adorned with a singular tuft of hairs; and the other a Clytus, I think, which Mr. MacLeay purchased from the late Mr. Marsham's collection, in which the hind-legs are not only very long, but have tarsi convolute, like some antennæ. From analogy I should affirm that these were the characters of male insects.

To come to the parts of legs. Sometimes the coxæ of the last mentioned sex are distinguished from those of the female by being armed by a mucro or spine. Thus the male of Megachile Willughbiella, and others of that tribe, have such a spine on the inner sides of the anterior coxa[849]. The Trochanter also of some differs sexually; and you will find that the posterior one of the male in Anthidium manicatum is of a different shape from what it is in the female[850]. In Sphodrus leucopththalmus, one of the beetles called black dors, in one sex the same trochanter terminates in a long mucro or spine[851], and in the other it is rounded at the apex.

Peculiar characters in their thighs also often indicate different sexes. In Prionus damicornis there is a short spine at the apex of the anterior ones in the female that is not in the male; while in Macropus longimanus, at their base externally the male is armed with a mucro, which I cannot find in the female[852]. In Scarabæus longimanus L. this thigh is furnished with two teeth[853].--The intermediate thighs also sometimes differ. In an Onitis from China, a variety perhaps of O. Sphinx, those in the male are dolabriform, and in the other sex of the ordinary shape. In Odynerus spinipes they have on their lower side two sinuses, so as to give them the appearance of being toothed. The posterior thighs are sometimes incrassated in the male, and not in the female. This you will see in a weevil, not uncommon, Apoderus Betulæ, and also in many species of Cimbex F., a kind of saw-fly; and the same circumstance distinguishes the latter sex in many species of Lygæus F., a kind of bug: I discovered this from L. cruciger, of which I have both the sexes; and from Stoll's figure of L. Pharaonis[854]. In some of these the female thighs are enormously large. A remarkable variation in this respect is observable in the coleopterous genus Œdemera (Necydalis L.). In Œ. Podagrariæ these limbs are incrassated in one sex and not in the other[855]; in Œ. cærulea they are so in both sexes; and in Œ. ceramboides in neither. In Pelecinus Polycerator F., one of the Ichneumon tribe, or an insect very near it from Brazil, these thighs in the female are armed with two spines underneath, which are not in the male.

The anterior tibiæ in Scarabæus longimanus L. differ remarkably in the sexes. In the female they are of the ordinary shape, and serrated externally; but in the male they are very long, incurved, and without teeth or serratures[856]. In the males of the genus Onitis F. they are bent like a bow, and acute at the end; but in the females they are formed on the common type[857]. In Hispa spinipes F. they are armed internally with a crooked spine[858]. But the most extraordinary sexual variation of this joint of the leg may be seen in the male of Crabro cribarius F. and several other species of the same family, in which these tibiæ are dilated externally into a concavo-convex plate, or rather have one fixed to them and part of the thigh, of an irregular and somewhat angular shape[859], with numerous transparent dots, so as not badly to resemble a sieve: whence the trivial name of the species. Rolander, who first described it, fancied that this plate was really perforated, and that by means of it the animal actually sifted the pollen; but it is most probably for sexual purposes. In another species, the plate is ornamented with transparent converging streaks. In the bee-tribes (Anthophila Latr.) the posterior tibia of the working sex is generally bigger than the corresponding part in their more idle partners: this is particularly conspicuous in the genus Euglossa, in the females of which this part is triangular, very broad towards the apex, and fitted for carrying a large mass of pollen paste. The tibiæ of the males of some Lepidoptera are remarkable in this respect. That of Hepialus Humuli is much more hairy; but in H. Hectus it is a dilated mis-shapen mass, without a tarsus, and with long scales pendent from the disk[860]. Differences of this kind also occur in the calcaria or spurs that arm the apex of the tibiæ of a large number of insects. Thus in Acanthopus Klug, a singular bee, in the male the spur of the intermediate leg is dilated at the apex, and armed with six strong spines, the inner one larger than the rest[861].

But the part of the leg in which the sexes most vary is the tarsus; and this variation takes place both in the number of the joints, and their form and circumstances. The first case has been observed only with regard to certain species of Cryptophagus Herbst, as C. fumatus, &c. in which the female is pentamerous, or having five joints in all the tarsi; and the male heteromerous, or having five joints in the two anterior pairs, and only four in the posterior[862]. With respect to the form of the tarsal joints, the sexes more frequently differ; and by inspecting this part, especially in the predaceous and carnivorous Coleoptera, you may often, without further examination, ascertain whether any individual is male or female. Even in the slender-footed Cicindelidæ, the three first joints of the anterior tarsus of the male are more dilated than the two last, and covered underneath with a brush of stiffish hair; in the female all are equally slender, and not so hairy. In Carabus, Feronia, &c. Latr. the four first joints of these tarsi in the males are dilated, and furnished with a brush or cushion: in the Silphidæ, also, the same circumstance takes place. In Harpalus Latr., and Silpha americana, the four anterior ones are similarly formed in this respect. But one of the most remarkable sexual characters, in this tribe of insects, that distinguish the males, are those orbicular patellæ, furnished below with suckers of various sizes, and formed by the three first joints of the tarsus, which are to be met with in the Dytiscidæ, &c.; but as I shall have occasion to treat of these more fully in another Letter, I shall only allude to them now. The second pair of tarsi have in these also the three first joints dilated and cushioned[863]. In Hydrophilus piceus, another water-beetle, the fifth joint of the tarsus is dilated externally, so as to form nearly an equilateral triangle[864]. Christian, a German writer on the Hymenoptera, has described some very singular appendages which he observed on the first joint of the four posterior tarsi of Xylocopa latipes F. These were battledore-shaped membranaceous laminæ, with a reticulated surface, of a pale colour; which were fixed in pairs by the intervention of a footstalk to the above joint, on which they sometimes amounted to more than a hundred: the use of which, he conjectures, is the collection of pollen[865]. I possess two specimens of this bee; one has none of these appendages, and on the other I can discover them only in one of the tarsi--from which circumstance I am led to conjecture that, like the supposed Clavariæ that were imagined to grow on some humble-bees, but which are now ascertained to be the anthers of flowers--these also belong to the kingdom of Flora, and are spoils which the bee in question has filched from the blossom of some plant. The individuals that have been thus circumstanced are males; whether the female is guilty of similar spoliations is not known. In my specimen there are no traces of them. In many bees, the first joint of the posterior tarsi is much larger in the females and workers than in the males; but in the hive-bee this joint is largest in the latter[866]. In Beris clavipes and Empis nigra, two flies, the joint in question is large and thick in the male, but slender in the female. The penultimate tarsal joint in the posterior legs is dilated internally, and terminates in a mucro in one sex of Anoplognathus Dytiscoides of Mr. W. MacLeay[867]. In some insects the anterior tarsus of the males has been supposed to be altogether wanting: I allude to the petalocerous genus Onitis F.; but I have a specimen of Onitis Apelles of this sex, or a species nearly related to it, in which one of these tarsi is to be found[868]; which, though very slender, consists of five joints, and is armed with a double claw: from which circumstance it may, I think, be concluded, that although, as in Phanæus, these tarsi are very minute, they are not wanting. What renders this more probable is, a circumstance which every collector of insects, who has many specimens of Mr. W. MacLeay's Scarabæidæ in his cabinet, must have noticed: namely, that in all, except Copris and Onthophagus, the anterior tarsi are usually broken off. Out of seventeen individuals of Scarabæus MacLeay in my own, not a single one has a relic of an anterior tarsus; and scarcely one in a much greater number of Phanæi. The tarsus in question in the nobler sex in Crabro, at least in C. cribrarius and its affinities, is also very short, especially the three intermediate joints; but at the same time very broad and flat. In the species just named, the external claw forms a kind of hook; and in the rest it is considerably longer than the other[869]. The claws, indeed, occasionally vary in the sexes in other Hymenoptera: thus in Melecta Latr., a kind of bee, in the female they are intire, but in the male they are furnished with an internal submembranaceous tooth or process[870]. In Cœlioxys conica and others, those of the latter sex are bifid at the apex, but those of the former acute[871]. In Megachile, the male claw is as in the instance just mentioned, while the female has a lateral tooth[872]; and a similar character distinguishes the sexes in the hive-bee[873].

3. The abdomen. This part affords many external sexual characters, whether we consider its general shape; the number of segments that compose it; its base, middle, or extremity.

In general shape it often differs in the sexes. Thus, the abdomen of female Tipulæ is lanceolate; that of the male cylindrical, and thickest at the extremity[874]. In Molorchus F. it is convex above in the former, and flat in the latter,--the female of this beetle not unaptly representing some female Ichneumons in this respect, and the male their males[875]. In Andrena it is oblong in the one, and lanceolate in the other. In the hive-bee the drones have a thick, obtuse, and rather long abdomen; in the females it is long, and nearly represents an inverted cone; and in the workers a three-sided figure, or prism.

The number of segments, also, is generally different in the two sexes--the male having one more than the female; but in Dytiscus marginalis, &c. the reverse of this takes place: the female, if you reckon the bipartite half-concealed anal segment as one, having seven ventral segments, and the male only six. She has also eight dorsal, and the male seven.--In the ant tribes (Formica L.), the little vertical scale, at the base of the abdomen in one description of them, or the double knot in another, is less in the male than in the female. In a very singular male insect belonging to the Vespidæ, and related to Synagris, (which I purchased from the late Mr. Drury's cabinet,) the second ventral segment sends forth from its disk two remarkable parallel very acute and rather long spines. The same sex of Chelostoma maxillosa has likewise on the same segment a concave elevation, opposite to which on the fifth is a cavity which receives it, when the animal rolls itself up to take its repose[876]. In another species, C. Campanularum, the segment in question has only a tubercle[877].

On the second segment of the abdomen of some specimens, probably males, of the remarkable African genus Pneumora before alluded to[878], there are thirteen little elevated ridges, placed rather obliquely in an oblique series; and gradually, though slightly, diminishing in size towards the belly: on their upper side they are flat, forming nearly a horizontal ledge, but on the lower they slope to the abdomen. The posterior thigh in its natural position covers the three first of them, and, if moved downwards, would strike them all[879]. I conjecture, therefore, that these are the animal's instruments of sound, imitating the harp or violin rather than the drum; and that the thigh acts the part of the hand or bow. The abdomen of these insects being blown out like a bladder, and almost empty[880], must emit a considerable sound when the thigh of the animal passes briskly over these ridges; and their different length would produce a modulation in the sound. When struck with a pin, they emit a grating noise.

In Staphylinus splendens, the penultimate ventral segment is very deeply cleft, and the antepenultimate emarginate in one sex, and intire in the other. In S. laminatus, an allied species, the penultimate segment is cleft, less deeply, however; but the antepenultimate is very short and intire; while the fourth is extremely long, and rounded at the margin, appearing as if it was only an elevated part of the last-mentioned segment; for which it was mistaken by Gravenhorst[881], while it is of the usual form in the other sex.

The extremity of the abdomen or its anal segments and organs furnish a variety of sexual characters. Sometimes the last dorsal segment is emarginate in the male, and not in the female; as in Megachile ligniseca, one of the leaf-cutter bees, Cimex hæmorrhoidalis, &c.[882] At other times little lateral teeth are added to this notch, as in another of the same tribe, M. Willughbiella[883]. Again, in other males, both the ventral and dorsal anal segment are armed each with a pair of teeth or mucros, as in Chelostoma maxillosa[884]. In Anthidium manicatum, another bee, the anus terminates in five spines[885]. In Cœlioxys conica of the same tribe, in which this part in the female is very acute, that of the male is armed with six points[886]. In that singular Neuropterous genus Panorpa, while the abdomen of the female is of the ordinary form, with a pair of biarticulate palpiform organs attached to the last retractile joint, or ovipositor, that of the male terminates in a jointed tail, not unlike a scorpion's, at the end of which is an incrassated joint armed with a forceps[887]. In the common earwig (Forficula auricularia) the two sexes differ considerably in their anal forceps: in one it is armed with internal teeth at the base, and suddenly dilated, above which dilatation it is bent like a bow: in the other it is smaller, without teeth, grows gradually narrower, is very minutely crenulate from the base to the end, and is straight, except at the very summit, where it curves inwards. Misled by these and similar differences, Mr. Marsham has considered them (the sexes both of F. auricularia and F. minor) as distinct species.

The tail of some species of the genus Ephemera is furnished with three long, jointed, hairy bristles. We learn from Reaumur with respect to one, that though in the female these are all equal in length, yet in the male there is only a rudiment of the third. On the belly near the anus these males have four fleshy appendages, the posterior ones setaceous and long, and the anterior pair filiform and shorter. They are supposed to represent the anal forceps of other insects[888]. In Ephemera vulgata, described by De Geer, both sexes have three bristles, but those of the male are the longest; and he describes the forceps as consisting of only a pair of jointed pieces, forming a bow not unlike the forceps of an earwig[889].

v. All the differences I have hitherto noticed between the sexes of insects occur in their bodily structure; but there are others of a somewhat higher description observable in their character. You may smile at the idea of character in beings so minute; but if you recollect what I formerly related to you when treating upon the societies of insects, you will allow that something of this kind does take place amongst them. In general the males are more fitted for locomotion and more locomotive; and the females, on the contrary, are necessarily more stationary. And this for an obvious reason:--the law is, that the male shall seek the female, and therefore he is peculiarly gifted for this purpose, both in his organs of sensation and motion: while his partner in many cases has very simple antennæ, he has very complex ones; and while she has either no wings or only rudiments of them, he is amply provided with them. Again: amongst the insects that suck the blood of man or beast, such as the gnat (Culex) or horse-flies (Tabanidæ), it is the female alone that is bloodthirsty, the males contenting themselves with the nectar of flowers[890]. But the difference of character in the sexes is most conspicuous, at least it has been more noticed, in those that live in societies, and is quite the reverse of what takes place in the human species. While the females and workers (which are now generally considered as sterile females, in which the ovaries are not developed) are laborious and active, diligent and skilful, wise and prudent, courageous and warlike;--the males, on the contrary, take no part in promoting the common weal, except merely a sexual one. Though till a certain period they are supported at the expense of the community, they take no part in its labours, either in collecting and forming the public stores, or in feeding and attending the young. They are idle, cowardly, and inactive; have neither art nor skill of any kind, and are unprovided with the usual offensive weapons of their species. These observations in their full force apply particularly to the hive-bee, and partially to the other social insects; amongst which, if you consult my former communications, there are some exceptions to this slothful character in the males[891].

II. Age. There is less diversity in the duration of the lives of insects in their perfect than in their larva or pupa state. Some, like several species of Ephemeræ, live only a few hours; some never even see the sun[892]: others, as flies, moths, and butterflies, and indeed the majority of insects, a few days or weeks; and a comparatively small number, such as some of the larger Coleoptera, Orthoptera, &c., six, nine, twelve, or fifteen months--a period beyond which the life of perfect insects rarely extends. Some, however, certainly enjoy a longer existence in the perfect state. Mr. Baker kept one of the darkling beetles (Blaps Mortisaga) alive under a glass upwards of three years. The rose-beetle (Cetonia aurata), Rösel informs us he fed with fruit and moist white bread for as long a period[893]. Esper kept our most common water-beetle (Dytiscus marginalis) in water in a large glass vessel, feeding it with meat, for three years and a half[894]. With regard to the Arachnida, from the very slow growth of Scorpio europæus, Rösel suspects that it must live two or three years; and Audebert is stated to have kept a spider for several[895]. In this respect insects follow a law very different from that which obtains amongst vertebrate animals. In these the duration of their life is in proportion to the term of their growth: those which attain to maturity the latest, in almost every case living the longest. In insects, on the contrary, we often meet with the very reverse of this rule. Thus the larva of the great goat-moth (Cossus ligniperda) is three years, that of the cabbage-butterfly (Pieris Brassicæ) not three months, in attaining maturity; yet the perfect insects live equally long. Melolontha vulgaris, which in its first state lives four years, as a beetle lives only eight or ten days[896]. And some Ephemeræ, whose larvæ have been two years in acquiring their full size, live only an hour; while the flesh-fly, whose larva has attained to maturity in three or four days, will exist several weeks.

There is yet another anomaly in the duration of the life of perfect insects. This is not, as in larger animals, a fixed period liable to be shortened only by accident or disease, and incapable of being prolonged; but an indeterminate one, whose duration is dependent on the earlier or later fulfilment of a particular animal function--that of propagation. The general law is, that a few days, or at most weeks, after the union of the sexes, both perish, the female having first deposited her eggs. If, therefore, this union takes place immediately after the disclosure of the insect from the pupa, their existence in the perfect state will not exceed a few days or weeks, or in some cases hours, as in that of the Ephemera, and likewise of the Phalænæ Attaci L. &c., which fall down dead immediately after oviposition[897]. But if by any means it be put off or prevented, their life may be protracted to three or four times that period. Gleditsch asserts, that by keeping apart the sexes of a grasshopper, their lives were prolonged to eight or nine weeks, instead of two or three, their ordinary length; and under similar circumstances Ephemeræ, which usually perish in a day, have been kept alive seven or eight. It is in consequence of this very curious fact, which has not received from physiologists the attention that it merits, that many butterflies and other insects, which, when excluded from the pupa in summer, perish in less than a month, live through the winter, if excluded late in the autumn, and the union of the sexes does not ensue. It is probable that the great age to which Baker's Blaps, Rösel's Cetonia, and Esper's Dytiscus attained, was owing to their being virgins when taken, and subsequently kept from any sexual intercourse. A parallel case happens in the vegetable kingdom:--if annual plants are kept from seeding, they will become biennial; as, likewise, if they are sown too late in the year to produce seeds.

In the case, however, of the earlier or later exclusion of the imago, another agent has probably some influence. Buffon found that, other circumstances being alike, the silkworm-moths placed in a northern, lived longer than those exposed to a southern aspect: whence it appears that the stimulus of heat shortens the lives of insects, and consequently that cold tends to lengthen them.

It must be observed too, that as the death of the female insect does not take place until all the eggs are excluded, the term of her life, though usually short in the majority of species, which lay their whole number at once, is proportionably long in those which, like the queen-bee, have a longer period assigned them for this important office. Huber affirms, that he had certain proofs that she was engaged for two years in laying eggs, all impregnated by a single sexual union[898]; and in the females of most insects that live in society, several months are required to mature the last eggs that are in the ovary. There is one tribe of insects, however, the females of which are affirmed to survive this operation: I mean Dorthesia Bosc; after which they even moult, though not so often as before[899].

I formerly related to you the singular fact, that the drones in a beehive at a certain period are without mercy slaughtered by the workers[900]. A fact the reverse of this is recorded by Morier with respect to the locusts: he affirms that the female, when she has done laying her eggs, is surrounded and killed by the males. He says that he never himself witnessed this extraordinary circumstance; but that he heard it from such authority that he gave full credit to it[901]. It is a fact, however, that seems to require further evidence to entitle it to such credit. These are instances in which, by a law of nature, the life of these insects is shortened by violence. It does not appear to have been ascertained how long those drones live that, under particular circumstances, as stated in a former letter[902], are exempted from the usual slaughter.

I am, &c.

FOOTNOTES:

[683] See above, VOL. II. p. 346.Return to passage

[684] Reaum. i. Mem. ult. De Geer i. 73. Swamm. Bibl. Nat. i. 184.Return to passage

[685] Swamm. Ibid.Return to passage

[686] Jurine Hymenopt. 16.Return to passage

[687] iv. 342. Herold also attributes the rapid expansion of the wing to the flow of an aqueous fluid, which he calls blood, into the nervures, the orifices of which open into the breast. Entwickelungs. der Schmetterl. 101. sect. 106.--M. Chabrier, in his admirable Essai sur le Vol des Insectes (Mém. du Mus. 4ieme, ann. 325), having observed a fluid in the interior of the nervures of the wings of insects, thinks it probable that they can introduce it into them and withdraw it at their pleasure: the object of which, he conjectures, is either to strengthen them and facilitate their unfolding, or to vary the centre of gravity in flight, and increase the intensity of the centrifugal force.Return to passage

[688] Ibid. 340.Return to passage

[689] Brahm. Insek. ii. 423.Return to passage

[690] Reaum. vi. 505--. t. xlvi. f. 9. Comp. De Geer ii. 627--.Return to passage

[691] Reaum. iii. 378.Return to passage

[692] Ibid. 385.Return to passage

[693] Insects of the beetle tribe, especially such as undergo their metamorphosis under ground, in the trunks of trees, &c., are often a considerable time after quitting the puparium before their organs acquire the requisite hardness to enable them to make their way to the surface. Thus, the newly-disclosed imago of Cetonia aurata remains a fortnight under the earth, and that of Lucanus Cervus, according to Rösel, not less than three weeks.Return to passage

[694] See above, VOL. I. p. 34--.Return to passage

[695] Jurine Hymenopt. 9. Note 1.Return to passage

[696] Oliv. N. i. t. i. f. 1. c. f. N. 3. t. iii. f. 22. a b c. t. v. f. 33. t. vi. f. 5. t. xiii. f. 124. a b.Return to passage

[697] Reaum. vi. 423.Return to passage

[698] Kirby Mon. Ap. Angl. ii. t. xvi. f. 12, 13. t. xvii. f. 10-12.Return to passage

[699] Reaum. iv. 393.Return to passage

[700] See above, VOL. I. 473--.Return to passage

[701] De Geer vii. 304.Return to passage

[702] Reaum. iv. 30.Return to passage

[703] Ibid. t. iv. f. 15.Return to passage

[704] See above, VOL. II. 36.Return to passage

[705] De Geer iii. 25.Return to passage

[706] Linn. Trans. iv. 54--.Return to passage

[707] ix. 65. n. 110.Return to passage

[708] vi. 423.Return to passage

[709] Entomologische, &c. 224.Return to passage

[710] De Geer ii. 847. 850. Jurine Hymenopt. 100.Return to passage

[711] Kirby Mon. Ap. Angl. ii. 296. 264.Return to passage

[712] Ibid. ii. 142--. 144, 147, 148, &c.Return to passage

[713] A remarkable anomalous exception to this rule sometimes occurs in the female of D. marginalis, which has smooth elytra like the male (Gyll. Ins. Suec. i. 467-). I have this variety from the Rev. Mr. Dalton, of Copgrove, Yorkshire.Return to passage

[714] De Geer i. t. vii. f. 11.Return to passage

[715] See above, VOL. II. 125, Note^b.Return to passage

[716] Melitta ** c. Kirby Mon. Ap. Angl. i. 140.Return to passage

[717] Ibid. t. iv. f. 10. a. b. f. 14.Return to passage

[718] Ibid. t. xiii. f. 20. a.Return to passage

[719] Kirby Mon. Ap. Angl. i. t. xi. Apis **. d. 2. α. β. f. 18 a. b. c. d.Return to passage

[720] Coquebert Illustr. Icon. i. t. vi. f. 6.Return to passage

[721] Kirby Mon. Ap. Angl. i. Apis **. c. 1. α. **. c. 1. β. **. c. 2. α. **. c. 2. β. **. c. 2. γ. **. c. 2. δ.Return to passage

[722] Ibid. t. viii. f. 28. f. g.Return to passage

[723] Christ. Hymenopt. t. iv. f. 3. b.Return to passage

[724] Kirby Mon. Ap. Angl. i. t. iv. Melitta **. c. f. 1. a.Return to passage

[725] Scheven Naturfors. stk. xx. 65. t. ii. f. 4. Compare Ibid. x. 101.Return to passage

[726] Reaum. iii. t. xv. f. 18, 19.Return to passage

[727] Oliv. no. 84. Brentus, t. i. f. 1. b. c. t. ii. f. 17. a. b.Return to passage

[728] Oliv. no. 3. Scarabæus, t. xviii. f. 169.Return to passage

[729] Oliv. Scarabæus, t. xii. f. 114. t. xv. f. 138. a.Return to passage

[730] Ibid. t. v. f. 33.Return to passage

[731] Ibid. t. xii. f. 112.Return to passage

[732] Linn. Trans. vi. t. xix. f. 12. t. xx. f. 2.Return to passage

[733] Oliv. no. 57. Tenebrio, t. i. f. 2.Return to passage

[734] Oliv. ubi supr. No. 3. t. i. f. 1.Return to passage

[735] Oliv. no. 3. t. iii. f. 20. a.Return to passage

[736] Ibid. no. 55. Diaperis, t. i. f. 3.Return to passage

[737] Oliv. Scarabæus, t. xx. f. 185.Return to passage

[738] As Dynastes Actæon, Elephas, Typhon, &c. differ from D. Hercules, &c., not only in their general habits, horns, &c., but also in their maxillæ and labium,--the former in D. Actæon being simple, and in D. Hercules toothed, and the labium of the first bilobed at the apex, and in the last entire and acute,--according to the modern system they ought, therefore, to be considered as distinct genera. I would restrict the name Dynastes to D. Hercules and its affinities: D. Actæon, &c. I would call Megasoma.Return to passage

[739] Oliv. Scarabæus, t. xvii. f. 156.Return to passage

[740] Ibid. t. viii. f. 63.Return to passage

[741] This insect is beautifully figured in M. Latreille's Insectes sacres des Egyptiens, f. 11. See Luke xi. 15. Heb. בעלןבול Dominus stercoris.Return to passage

[742] Oliv. no. 83. 160. t. vi. f. 60. ♂. t. v. f. 45. ♀?Return to passage

[743] Ibid. no. 36. t. ii. f. 12.Return to passage

[744] Ibid. no. 6. t. vii. f. 61.Return to passage

[745] See above, VOL. II. 224--.Return to passage

[746] Coquebert Illustr. Icon. iii. t. xxi. f. 2.Return to passage

[747] Stoll Cigales, t. xviii. f. A B C. Grillons t. iv. f. 16-18. This singular animal, which was found by Mr. Patterson at the Cape of Good Hope, is stated to be an aquatic; and affords the only known instance of an Orthopterous insect inhabiting the waters. The Gryllotalpa loves the vicinity of water.Return to passage

[748] Mon. Ap. Angl. i. Melitta **. b. 139. t. ii. f. 4-6.Return to passage

[749] Ibid. **. a. f. 4, 5.Return to passage

[750] Ibid. Apis *. b. 190--. t. v. f. 18 b.Return to passage

[751] By Rösel, by a friend of De Geer's, and by M. Marechal. De Geer iv. 331--. Nouv. Dict. d'Hist. Nat. xviii. 225.Return to passage

[752] Oliv. no. i. Lucanus, t. ii. f. 3.Return to passage

[753] Ibid. t. iii. f. 7.Return to passage

[754] Linn. Trans. xii. 410. t. xxi. f. 12.Return to passage

[755] Ibid. vi. 185. t. xx. f. 1.Return to passage

[756] Oliv. ubi supr. t. ii. f. 4.Return to passage

[757] Regne Animal, iii. t. xiii. f. 3.Return to passage

[758] See VOL. I. PLATE I. FIG. 3.Return to passage

[759] Christ. Hymenopt. t. xviii. f. 2.Return to passage

[760] Mon. Ap. Angl. i. Melitta *. a. t. i. f. 5. ♀. 7. ♂.Return to passage

[761] Ibid. Melitta **. a. t. ii. f. 6. ♀. 7. ♂. and **. b. t. iii. f. 3. ♀. 4. ♂.Return to passage

[762] Ibid. t. viii. f. 11. ♀. 12. ♂.Return to passage

[763] Ibid. i. t. viii. f. 9. ♀. 10. ♂.Return to passage

[764] Ibid. Apis **. c. 2. β. t. ix. f. 6. ♀. 7. ♂.Return to passage

[765] See above, VOL. II. 125. Note^b.Return to passage

[766] Mon. Ap. Angl. ubi supr. t. xiii. f. 13. ♀. 14. ♂.Return to passage

[767] MacLeay Hor. Entomolog. 4--.Return to passage

[768] N. Dict. d'Hist. Nat. xxii. 488.Return to passage

[769] Linn. Trans. xii. 425--. t. xxii. f. 6.Return to passage

[770] PLATE XXVI. FIG. 2.Return to passage

[771] Ibid. FIG. 3.Return to passage

[772] Oliv. no. xxv. Lymexylon, t. 1. f. 1.Return to passage

[773] De Geer vii. 249--. t. xiv. f. 20, 21. Treviranus Arachnid. 36--. t. ii. f. 16. a b c. t. iv. f. 35-37.Return to passage

[774] Mon. Ap. Angl. i. Apis **. c. 2. γ. t. ix. f. 7. ♀. 9. ♂.Return to passage

[775] Ibid. Melitta **. a. t. ii. f. 8. ♀. 9. ♂. and **. b. t. iii. f. 6. ♀. 7. ♂. **. c. t. iv. f. 11. ♀. 12. ♂.Return to passage

[776] Jurine Hymenopt. t. 11. f. 2.Return to passage

[777] Mon. Ap. Angl. i. Apis **. d. 1. t. x. f. 7.Return to passage

[778] Oliv. no. 80. Macrocephalus, t. i. f. 2.Return to passage

[779] Latr. Gen. Crust. et Ins. iv. 156.Return to passage

[780] Jurine Hymenopt. 61. t. vi. f. 8.Return to passage

[781] Ibid. 289.Return to passage

[782] Mon. Ap. Angl. i. t. ix. Apis **. c. 2. γ. f. 9.Return to passage

[783] PLATE XI. FIG. 19.Return to passage

[784] PLATE V. FIG. 3.Return to passage

[785] PLATE XI. FIG. 18.Return to passage

[786] Ibid. FIG. 17.Return to passage

[787] PLATE XXV. FIG. 11. Linn. Trans. xii. t. xxi. f. 4. a.Return to passage

[788] Ibid. f. 3.Return to passage

[789] PLATE XXV. FIG. 22.Return to passage

[790] De Geer i. t. xix. f. 11, 12.Return to passage

[791] Jurine Hymenopt. t. vi. f. 8.Return to passage

[792] PLATE XXV. FIG. 25, 26.Return to passage

[793] Ibid. FIG. 4.Return to passage

[794] Reaum. iv. t. xl. f. 2. a a. ♂. t. xxxix. f. 3. ♀. In the last the hairs are too conspicuous.Return to passage

[795] PLATE XII. FIG. 24.Return to passage

[796] Jurine Hymenopt. t. vi. f. 3.Return to passage

[797] PLATE XII. FIG. 25, 26. XXV. FIG. 17, 32.Return to passage

[798] Ibid. FIG. 12.Return to passage

[799] PLATE XI. FIG. 22.Return to passage

[800] N. Dict. d'Hist. Nat. xiv. 395.Return to passage

[801] PLATE XII. FIG. 7.Return to passage

[802] PLATE XXV. FIG. 1.Return to passage

[803] Ibid. FIG. 21.Return to passage

[804] Linn. Trans. xii. t. xxii. f. 8. e. ♂. f. ♀.Return to passage

[805] Hist. Nat. des Fourmis, 195--. 270--.Return to passage

[806] De Geer ii. 1094.Return to passage

[807] Ibid. 650. Mon. Ap. Angl. i. t. xi. Apis xx. c. 1. f. 2. ♂. t. xii. f. 3. ♀.Return to passage

[808] PLATE XXVI. FIG. 39. De Geer ii. 651. 659.Return to passage

[809] Voet Coleopt. i. t. xxxix. f. 47, 48. ♂. 46. ♀.Return to passage

[810] Oliv. no. 3. t. vi. f. 46. a. ♂. b. ♀.Return to passage

[811] Ibid. t. i. f. 1. iv. x. f. 31. xi. f. 102. xii. f. 114.Return to passage

[812] Ibid. t. xxvi. f. 219.Return to passage

[813] Ibid. t. i. f. 2.Return to passage

[814] Ibid. t. xxiii. f. 35.Return to passage

[815] Ibid. t. ii. f. 7.Return to passage

[816] Ibid. t. v. f. 40.Return to passage

[817] Ibid. xix. f. 175.Return to passage

[818] Ibid. t. xii. f. 115.Return to passage

[819] Copris floriger Kirby in Linn. Trans. xii. 396.Return to passage

[820] Oliv. no. 3. t. ii. f. 18.Return to passage

[821] Ibid. t. xxii. f. 32.Return to passage

[822] Ibid. t. ix. f. 85.Return to passage

[823] Ibid. t. iii. f. 22.Return to passage

[824] Ibid. t. xiii. f. 124. a.Return to passage

[825] Ibid. t. v. f. 38.Return to passage

[826] Ibid. t. xxviii. f. 242. t. xviii. f. 169.Return to passage

[827] Ibid. t. xvi. f. 152.Return to passage

[828] Ibid. t. xxviii. f. 247.Return to passage

[829] Ibid. t. xv. f. 138. a. t. v. f. 33.Return to passage

[830] Samouelle's Compend. t. i. f. 1.Return to passage

[831] Oliv. no. 3. t. v. f. 36. a.Return to passage

[832] Schon. Synon. i. t. 1.Return to passage

[833] Oliv. no. 3. t. xxiv. f. 208.Return to passage

[834] Ibid t. x. f. 88.Return to passage

[835] Ibid. f. 87.Return to passage

[836] Ibid. t. xx. f. 185.Return to passage

[837] Ibid. t. vi. f. 42. a.Return to passage

[838] Ibid. n. 83. Curculio t. xxii. f. 295.Return to passage

[839] Oliv. no. 81. Attelabus t. ii. f. 27. b. 28.Return to passage

[840] De Geer ii. t. xxxi. f. 18-22.Return to passage

[841] Ibid. iii. 21.Return to passage

[842] Lesser L. i. 185.Return to passage

[843] De Geer iii. 308.Return to passage

[844] See above, VOL. II. 394--.Return to passage

[845] Linn. Trans. i. 145. 135--.Return to passage

[846] Ibid. t. xiii. f. 1. 2. ♂. 3. ♀.Return to passage

[847] Mon. Ap. Angl. i. t. xi. Apis **, a. 2. α. β. f. 18.Return to passage

[848] Oliv. no. 68. Saperda t. i. f. 8.Return to passage

[849] Mon. Ap. Angl. i. t. viii. f. 28. c.Return to passage

[850] Ibid. t. ix. Apis **. c. 2. β. f. 12.Return to passage

[851] Clairv. Ent. Helv. ii. t. xii. f. B.Return to passage

[852] Oliv. Ins. no. 66. t. iii. iv. f. 12.Return to passage

[853] Ibid. no. 3. t. iv. f. 27.Return to passage

[854] Punaises, t. iii. f. 20.Return to passage

[855] Mr. Marsham has made two species of this from this circumstance, viz. Necydalis Podagrariæ and simplex.Return to passage

[856] Oliv. n. 3. t. xxvii. f. 27. ♀. and t. iv. f. 27. ♂.Return to passage

[857] Ibid. t. vii. f. 58. ♂. f. 57. ♀.Return to passage

[858] Ibid. n. 95. Hispa t. i. f. 4. PLATE XXVII. FIG. 24.Return to passage

[859] PLATE XV. FIG. 3.Return to passage

[860] De Geer i. t. vii. f. 14, 15.Return to passage

[861] Coquebert Illust. Icon. i. t. vi. f. 6. PLATE XXVII. FIG. 32.Return to passage

[862] Illig. Mag. iv. 214. Gyllenhal. Insect. Suec. i. 168.Return to passage

[863] PLATE XV. FIG. 9.Return to passage

[864] Ibid. FIG. 8.Return to passage

[865] Christ. Hymenopt. 118. t. iv. f. 3.Return to passage

[866] Mon. Ap. Angl. i. t. xi. Apis **. e. 1. ♂. f. 8. e. and t. xii. **. e. 1. neut. f. 19. c.Return to passage

[867] Hor. Entomolog. 144.Return to passage

[868] PLATE XXVII. FIG. 45. a.Return to passage

[869] De Geer ii. t. xxviii. f. 2.Return to passage

[870] Mon. Ap. Angl. i. t. v. Apis **. a. f. 10. ♂. 11. ♀.Return to passage

[871] Ibid. t. vii. Apis **. c. 1. α. 17. ♀. 18. ♂.Return to passage

[872] Ibid. t. viii. f. 30. ♂. 31. ♀.Return to passage

[873] Ibid. t. xi. Apis **. e. 1. mas. f. 9. t. xii. Apis **. e. 1. fem. f. 9. and neut. f. 22.Return to passage

[874] De Geer vi. t. xviii. f. 12, 13.Return to passage

[875] De Geer v. 151--.Return to passage

[876] Mon. Ap. Angl. i. 177. t. ix. Apis **. c. 2. γ. f. 11. a, d.Return to passage

[877] Ibid. f. 13. a.Return to passage

[878] See above, VOL. II. 395.Return to passage

[879] PLATE XXIX. FIG. 13. Stoll. Spectres, &c. t. xxv. f. 99.Return to passage

[880] Sparrman. Voyage, i. 312--.Return to passage

[881] Coleopt. Micropt. 16.Return to passage

[882] Mon. Ap. Angl. i. t. viii. f. 25. De Geer iii. 255. t. xiv. f. 8.Return to passage

[883] Mon. Ap. Angl. i. t. viii. f. 24.Return to passage

[884] Ibid. t. ix. Apis xx. c. 2. γ. f. 12.Return to passage

[885] Ibid. Apis **. c. 2. β. f. 11.Return to passage

[886] Ibid. t. vii. Apis **. c. 1. α. f. 11, 12. ♀. 13, 14. ♂.Return to passage

[887] PLATE XV. FIG. 12. De Geer ii. t. xxiv. f. 9, 10. ♀. t. xxv. f. 2, 3. ♂.Return to passage

[888] Reaum. vi. 494. t. xliv. f. 3-11.Return to passage

[889] De Geer ii. t. xvii. f. 5-7.Return to passage

[890] N. Dict. d'Hist. Nat. xxxii. 443.Return to passage

[891] See above, VOL. II. 110, 118.Return to passage

[892] VOL. I. 283.Return to passage

[893] II. i. 6.Return to passage

[894] Clairville Ent. Helvet. ii. 214--. I have seen it asserted in some popular work on Natural History, (the title of which I do not recollect,) that Mantis religiosa has been known to live ten years; and a flea, when fed and taken care of, six. But this is so contrary to experience in other cases, that the statement seems quite incredible.Return to passage

[895] Rösel III. 379. N. Dict. d'Hist. Nat. ii. 285.Return to passage

[896] Dumeril Traité Elément. ii. 87. n. 683.Return to passage

[897] De Geer ii. 288.Return to passage

[898] Huber i. 106.Return to passage

[899] N. Dict. d'Hist. Nat. ix. 553.Return to passage

[900] VOL. II. 173--.Return to passage

[901] Morier's Second Journey through Persia, 100.Return to passage

[902] VOL. II. 175.Return to passage