Letter XXX

Letter XXX

STATES OF INSECTS.

LARVA STATE.

The Larva state is that in which insects exist immediately after their exclusion from the egg (or from the mother in ovo-viviparous species), in which they usually eat voraciously, change their skin several times, and have the power of locomotion, but do not propagate.

Almost all larvæ, at their birth, are for a time in a very feeble and languid state, the duration of which differs in different species. In most it continues for a very short time, a few minutes or perhaps hours, after which they revive and betake themselves to their appropriate food. In others, as in the generality of spiders, this debility lasts for seven or eight days, and in some species even a month, during which the young ones remain inactive in the egg-pouch[206], and it is not till they have cast their first skin that their active state of existence commences.

All larvæ may be divided into two great divisions:--

I. Those which in general form more or less resemble the perfect insect.

II. Those which are wholly unlike the perfect insect.

I shall begin by calling your attention to the characters of the first of these divisions: the second, which is by far the most numerous, will be afterwards considered.

I. The first division includes the larvæ of Scorpions, Spiders, Cockroaches, Grasshoppers, Lanthorn-flies, Bugs, &c.; or generally, with the exception of the Flea and Crustacea, the whole of the Linnean Orders Aptera and Hemiptera. All these larvæ, however remotely allied in other respects, agree in the general similarity which they bear to the perfect insects which proceed from them. The most acute entomologist, untaught by experience, could not even guess what would be the form of the perfect insects to be produced from larvæ of the second division, while they can recognise the form of the spider, the cricket, the cockroach, the bug, and the frog-hopper, in that of the larvæ. There are, however, differences in the degrees of this resemblance, according to which we may, perhaps, divide this tribe in their second state as follows:--

i. Those that resemble the perfect insect, except in the relative proportions and number of some of their parts.

ii. Those which resemble the perfect insect, except that they are apterous, or not yet furnished with organs of flight.

i. Spiders, Phalangia, scorpions, lice, Poduræ, sugar-lice (Lepisma), mites, centipedes, millepedes, &c. come under the first subdivision. The larvæ of the first six tribes here mentioned differ at their birth from the perfect insect, only in size and the proportions of their parts. Thus the larvæ of spiders have their legs of a different relative length from that which they subsequently acquire; and the palpi in the males, which previously to the discoveries of Treviranus were regarded as their sexual organs, are not yet fully developed[207]: and a similar difference takes place in the legs of Phalangia. The general form too of the body undergoes slight alterations, and the colour very considerable ones, with each change of the skin--a change to which all these tribes are subject.

The larvæ of the three last-mentioned tribes (the mites, centipedes, and millepedes) differ from the perfect insect not only in the proportion but also in the number of their parts. Leeuwenhoeck states (and De Geer confirms his assertion, extending it to other species of mites[208]), that the common cheese-mite, which in its perfect state has eight legs, when first excluded from the egg has but six, the third pair being wanting[209]. Some however are born with eight legs, for instance A. eruditus of Schrank, which he saw come from the egg itself with that number[210]. Others again have never more than six legs: this is the case with Latreille's genera--Caris, Leptus, Atoma, and Ocypetes of Dr. Leach[211]. In the centipedes (Scolopendridæ) and millepedes (Iulidæ) differences still more remarkable, as I have stated in a former letter, have been observed by De Geer; these animals, in their progress to the perfect state, not only gain several additional pairs of legs, but also several additional segments of the body. This illustrious Entomologist found that Pollyxenus lagurus (Scolopendra L.) was born a hexapod, with but three segments and as many pairs of feet, but successively acquired five additional segments with other appendages, and nine more pairs of feet[212]. A species of millepede (Iulus terrestris L.), which he also traced from its birth, and which begins the world at first with only eight segments and six feet, by a successive development at length acquires, in its perfect state, 50 segments and not less than 200 feet[213]. The nature of these very singular accretions, which Latreille and Mr. Wm. MacLeay have also observed in the centipedes[214], seems not well understood. If, as is most probable, though De Geer could not find any exuviæ[215], the larvæ cast a skin before each change, they do not essentially differ from the metamorphosis of other insects. The legs that these insects thus acquire are affixed to the abdomen, the six that they set out with being attached to the part representing the trunk, so that the former may be regarded as analogous to the prolegs of caterpillars. These animals therefore, as I have before intimated, invert the order of Nature, and from perfect degenerate into imperfect insects.

ii. If you examine the cockroach, cricket, or grasshopper, in different stages of their growth, you will find that the larva does not vary essentially from the perfect insect, except in wanting wings and elytra. The case is the same in almost all the Linnean genera of the modern order--Hemiptera; and with Raphidia, Termes, and Psocus, in the Neuroptera. Some of these, however, exhibit slighter discrepancies in the proportion of some of their parts, but without affecting the general resemblance. Thus the larvæ of the common ear-wig have at first only eight, and subsequently nine joints to their antennæ, whereas the perfect insect has fourteen[216]; and the forceps is quite different, resembling rather two straight styles than what its name implies. In those also of many bugs (Coreus marginatus F. &c.), the joints of the antennæ are of a shape dissimilar to that which obtains in the perfect insect. In that of the common water-scorpion, the anal air-tube, which is so long in the imago, is scarcely visible[217]. In the Cicada tribe, so celebrated for their song[218], neither the larva nor the imago have the enormous thigh armed below with strong teeth, the tibiæ terminating in a fixed incurved claw, probably for the purpose of digging the holes into which they retire till they disclose the fly, which distinguish the pupæ of some species, and is particularly conspicuous in one commonly brought from China[219]. These often exhibit also other minor differences.

II. In treating of the second great division of larvæ, those that are wholly unlike the parent insect,--which includes, with few exceptions[220], the whole of the Linnean orders, Coleoptera, Lepidoptera, Hymenoptera, Diptera, the majority of the Neuroptera, Coccus and Aleyrodes in Hemiptera, and the genus Pulex in Aptera,--I shall advert to their characters, under several distinct heads; and to avoid unnecessary circumlocution, I shall in what follows wholly leave out of consideration the first division already explained, and use the term larvæ with reference only to those of the second. The heads under which I propose to treat of them are: The substance of their body, its parts, shape, or figure, clothing, colour. Also the Economy or mode of life of these creatures: their food, moultings, growth, age, sex, and their preparations for assuming the Pupæ.

i. Substance, with the exception of the head and six fore-feet, which are usually corneous, the exterior integument or skin of larvæ is commonly of a membranous texture, and the body is of a much softer consistence than in the perfect insect. In those, however, of some Staphylinidæ and other Coleoptera, the dorsal part of the three first pieces, which represent the trunk of the perfect insect, is hard and horny. Some also have their whole skin coriaceous, as the tortoise-shell butterfly (Vanessa polychloros); and some few, as the wire-worm (Elater segetum), and other Elateres, very hard. I possess a very remarkable larva from Brazil, from the extreme flatness of its body, and from its having cavities to receive its legs when unemployed, probably living under bark, the skin of which is still harder than that of the grub of the Elaters. Perhaps it has to resist great pressure; and on that account is gifted with this quality, so seldom to be met with in other kinds of larvæ. The interior of the body of these animals is generally of a softer consistence than in the perfect insect. Their intestines, and other internal organs, are usually wrapped in a voluminous substance of a fatty nature, which is regarded as analogous to the epiploon, omentum, or caul, which envelops the viscera of quadrupeds, &c., and is called by Reaumur the corps graisseux. The use of this general flexibility of larvæ is obvious; for, their bodies being mostly long and narrow, a hard rigid covering would have been very inconvenient, and a considerable impediment to their motions. When a caterpillar is feeding, it has occasion to apply its body to any part of the margin of a leaf so as to support itself by its prolegs, and when moving it wants to give it all the curves that are necessary to enable it to avoid obstacles, and thread its way through the sinuous labyrinths which it must often traverse. On the other hand, the hardness of the substance of its head affords a strong fulcrum to the muscles which keep its powerful jaws in constant play. The larvæ, indeed, of some Diptera have a membranous head; but their mandibles, which serve also as legs, are not grinders, but merely claws, the muscles of which require less powerful support[221]. Under this head it may be proper to observe, that generally larvæ are opaque; but some, as those of ants, and a few Lepidoptera[222], are diaphanous. That of Corethra crystallina (Tipula De Geer) is so beautifully transparent as to resemble a piece of crystal, and scarcely to be distinguished from the water in which it lives[223].

ii. Parts. The body of each larva consists of the head, including its different organs, and of the succeeding segments, of which the three first may usually be denominated the trunk, and have the six anterior feet, when present, attached to their under side: the remainder is the abdomen. The latter includes in some species a variable number of membranous feet, as well as various appendages affixed usually to its tail and sides. No larva is ever furnished with wings[224]. Each of these greater divisions, and the organs which they include, require separate consideration.

1. Head. This, as was lately observed, is exteriorly of a horny substance, or at least harder than the rest of the body, in most larvæ; and on this account, though rarely separated from it by any visible distinct neck[225], is, if the larva be of a tolerable size, distinguished at the first view. In those of many Dipterous insects, however, the head is covered with the same flexible membranous skin with the rest of the body, from which it is often scarcely to be distinguished. In these, except that it contains the organs of manducation, it wears no more the appearance of a head than any other segment of the body, and scarcely so much as the last or anal one. The head of these larvæ is also remarkable for another peculiarity,--that it is capable of being extended or contracted, and assuming different forms at the will of the insect: a property which the head of no superior animal can boast. It is probable that there is a considerable variety in the shape and circumstances of the heads of larvæ; but since, with the exception of those of Lepidoptera, they have had less attention paid to them than they deserve (indeed in a vast number of cases, from the difficulty of meeting with them, these variations, except in a few instances, have not been described), I will here mention a few of the most remarkable. The head of the young larva at its first exclusion from the egg is usually the most dilated part of the body, but it does not often continue so. In that of Cicindela campestris, however,--the beautiful green beetle sometimes found in sandy banks,--and also in several caterpillars of Lepidoptera, it is much larger than any of the following segments[226], which, in conjunction with the animal's formidable jaws, gives it a most ferocious appearance. In some lepidopterous larvæ the head is of the same diameter with the rest of the body, but in insects in general it may, I think, be stated as less; and occasionally it bears no proportion whatever to it. This is the case with the subcortical one from Brazil lately mentioned. It is more commonly longer than broad; but in some, as in the larvæ of carrion beetles (Silphæ), the reverse of this takes place. Its shape varies from triangular to orbicular, the mouth of the animal forming the vertex of the triangle. In some larvæ of Hemerobii, however, the head is narrowest behind. That of the grub of a gnat noticed above (Corethra crystallina) forms a kind of sharp horn or claw, terminating the body anteriorly[227]. The contour of the head of larvæ is usually intire and unbroken; but in the caterpillars of some Lepidoptera, as the butterfly called the grand admiral (Vanessa Atalanta), the Glanville fritillary (Melitæa Cinxia), &c. it is divided into two lobes[228]. In the Brazil flat larvæ it is trilobed, each lateral lobe being divided into three smaller ones: in which circumstance it somewhat resembles the head of some subcortical Cimicidæ. Although the part we are treating of is generally without horns, yet in some tropical butterflies of the tribe of Nymphales, it is singularly armed with them. Thus Papilio Anchises is distinguished, according to Madame Merian[229], by two in the occiput, which it has the power of retracting. In the purple highflier (Apatura Iris), a British species, the two lobes of the head, I am informed, terminate behind in two horns; as they do likewise in the brilliant Morpho Menelaus[230], the lobes assuming the form of a pear, and the horn representing the stalk. In a caterpillar I found amongst Mr. Francillon's larvæ, the head is bilobed, with a very long recurving subcapitate subramose spine. In Satyrus Cassiæ, the head is armed with three occipital stout spines[231]. The larva of Nymphalis Amphinome Latr. (Limenitis F.) is crowned with a coronet of eight occipital stout acute spines, the intermediate ones being the longest[232]; and that of Morpho Teucer has a similar coronet, consisting of only seven blunt rays, seemingly, rather than spines[233]. With regard to the articulation of the head with the trunk, it is generally by its whole diameter; but in some instances, only by a part of it. This is the case with one of a sphinx figured by Mad. Merian[234]; and I have another, probably belonging to the nocturnal Lepidoptera (Phalæna L.)[235]. In both these, the head is vertical and triangular; and in the latter (which is a remarkable creature, the tail itself being more like a head, and furnished with what resemble two prominent black eyes) the vertex of the triangle is considerably higher than the back of the animal. Whatever may be the clothing of the body, the head is usually naked. Sometimes, however, it is itself beset with very small simple spines, as in the butterfly of the mallow (Hesperia Malvæ); or with longer compound ones, such as are found on the rest of the body. This is the case with one of a butterfly named by Rösel Papilio morsa. The most common colour of the head of larvæ, where it differs from the rest of the body, is a darker or lighter reddish brown, or piceous. This is particularly observable in those of Coleopterous insects, but it is very commonly in other tribes of the same hue. Sometimes, amongst the Lepidoptera, the head is of a different colour from the rest of the body; especially where a contrast renders it striking. I can show the caterpillar of some insect, probably of the hawk-moth tribe (Sphingidæ), from Georgia, remarkable for the length of its anal spine, in which the body is black, and the head red: another has a white head and a brown body. In the larvæ of some Lepidoptera, Coleoptera, and Diptera, the head can be wholly or nearly withdrawn within the first segment of the body. This may be readily seen in that of the common glow-worm; and that of a small gnat (Tipula replicata De Geer) withdraws it so completely that the anterior margin of that segment closes the orifice, so that the animal appears to have no head[236].--The parts of the head which require distinct consideration are, the eyes, antennæ, and the mouth: consisting of various organs, which will be specified. Some of these parts and organs are peculiar to larvæ of one order, others to those of another, and some are furnished with them all.

Eyes. The larvæ of many insects have no eyes. Those with antennæ which terminate in a lamellated clava (Scarabæus L.), and capricorn beetles also (Cerambyx L.), amongst the Coleoptera, are without them, and probably several others; and amongst the Diptera, all those with a membranous or variable head. Those of the remaining orders, with the exception, perhaps, of some Hymenoptera and Lepidoptera, are furnished with these organs; and in the Coleoptera all the predaceous tribes, as well as most of those that are herbivorous or granivorous, and the Gnats and other Tipulidans (Tipulariæ Latr.) in the Diptera, are also distinguished by them. In the larvæ of the dragon-flies (Libellula L.), and other Neuroptera, they are composed of many facets as in those of the perfect insect, from which they differ chiefly in being smaller. But in the other insects of this description they are simple, and resemble those of the Arachnida, and many aptera. These simple eyes vary in their number, in different genera and tribes, from one to six on each side of the head. Thus the larva of Telephorus, and the saw-flies, has only one[237]; that of Cicindela three, the two posterior ones being large with a red pupil surrounded by a paler iris, which adds to the fierce aspect of this animal; and the anterior one very minute. Those of the tortoise-beetles also (Cassida) have three[238]; of Staphylinus, four; of Timarcha (the bloody-nosed beetle) five; of Carabus, and the Lepidoptera in general, six. In the last they are of different sizes, and generally arranged in a circle: in that of Hemerobius there are five in a circle, with one central one[239]. The appearance of these globules, which are often not visible but under a powerful lens, is so different from that of the eyes of a butterfly or moth, or other perfect insect, that it has been doubted whether they actually perform the office of eyes, but without reason. They occupy the usual station of those organs, being situated in many instances upon a protuberance which appears to incase them; and seem of a construction closely analogous to that of the eyes of spiders, and the stemmata or ocelli of Hymenoptera, which have been satisfactorily proved to be organs of vision. In the larva of a moth not yet ascertained to exist in this country, Attacus Tau, and probably other species, the eyes, after the skin has been changed a few times, are no longer to be seen[240].

Antennæ. Most larvæ are provided with organs near the base of the mandibles, which from their situation and figure may be regarded as antennæ. Fabricius has asserted that the larvæ of the saw-flies (Tenthredo L.) have no antennæ; but in this he was mistaken, for though very short, they are discoverable in them, as he might have learned by consulting De Geer[241]. In the majority of Neuropterous larvæ, they almost precisely resemble those of the perfect insect. In all the rest they are very different. The antennæ of Coleopterous larvæ are usually either filiform or setaceous, consisting of four or five joints, nearly equal in length. Those of Lepidopterous larvæ are commonly conical, as are those likewise of Chrysomela and Coccinella &c. amongst the Coleoptera, and very short, composed of two or three joints, of which the last is much thinner than the first, and ends in one or two hairs or bristles. These antennæ the larva has the power of protruding or retracting at pleasure. Lyonnet informs us, that the caterpillar of the great goat-moth (Cossus ligniperda) can draw the joints of its antennæ one within the other, so as nearly to conceal the whole[242]. The larva of the common gnat has two long incurved setaceous antennæ, fringed with hairs at some distance from their apex, which consist only of a single joint[243]. The greater number of Dipterous larvæ, however, all indeed except the Tipulidans (Tipulariæ Latr.), and many belonging to the Coleoptera and Hymenoptera orders (as those of Curculio, Apion, Apis, &c.), are wholly deprived of antennæ. It is a general rule, that the antennæ of larvæ are shorter than the same organs in the perfect insect, the tribe Ephemerina perhaps affording the only example in which the reverse of this takes place[244].

Mouth. All larvæ have a mouth situated in the head, by which they receive their food, and furnished with one or more instruments for the purpose of mastication and deglutition. These instruments, in all the orders except Lepidoptera, some Neuroptera and Diptera, bear a general resemblance to the same parts in the perfect insect. In larvæ of the Coleopterous, Lepidopterous, and Hymenopterous orders, we can distinguish for the most part an upper and under lip; two pairs of jaws answering to the mandibulæ and maxillæ; and two, four, or six palpi[245]: and some of these instruments may be found in most Diptera. Each of these parts require separate notice.

Upper-lip (LABRUM). The mouth of almost all larvæ, except some of the order Diptera, are provided with a distinct upper-lip, for retaining their food during mastication. As the construction of this part does not widely differ from that of the perfect insect, which will hereafter be more fully described, it is only necessary to observe, that it is usually a transverse moveable plate, attached posteriorly to the nasus (clypeus F.), and situated just above the mandibles[246].

Upper-jaws (MANDIBULÆ). The most usual figure of these, which are of a hard horny consistence[247], is that of two slightly concave, oblong, or triangular plates, often at their lower extremity of considerable thickness, and of very irregular form, the base of which is filled with powerful muscles, and planted in the side of the mouth so as to move transversely. The other extremity can be made to meet or diverge like the claws of pincers, and are divided into one or more tooth-like indentations, by means of which the food of the larva is cut[248]. This is their construction in the larvæ of all Lepidoptera, and in many of those of the other orders. They frequently, however, assume a different form, though their situation is always the same. Thus in the larvæ of the capricorn beetles (Cerambyx L.) and of other wood-boring species, they are shaped like the half of a cone, the inner sides of which, applying close to each other, form a pair of powerful grindstones, capable of comminuting the hardest timber[249]. M. Cuvier has observed, with regard to the mandibulæ of those of stag-beetles (Lucanus), that besides their teeth at the extremity, they have towards their base a flat striated molary surface; so that they both cut and grind their ligneous food[250]. It seems to have escaped him, that a similar structure takes place in many perfect insects of the lamellicorn tribe, as I shall hereafter show you. In the larvæ of the water-beetles (Dytiscus L.), ant-lions (Myrmeleon L.), and lace-winged flies (Hemerobius L.), they resemble somewhat the forceps at the tail of an ear-wig, being long and incurved; and, what is more remarkable, hollow and perforated at the end, so as to serve as a channel for conveying into the larva's mouth the juices of the prey which by their aid it has seized. Reaumur even asserts, that the larva of Myrmeleon has no other entrance into its throat than through these tubular mandibles[251]. That of the rove-beetles (Staphylinus L.), and of many other Coleopterous genera, have these organs of this forcipate construction, without being perforated[252]. In the larva of the carnivorous flies, and many other Diptera, are two black incurved subulate parts, connected at the base, and capable of being protruded out of, and retracted into, the head, through the skin of which they are usually visible. As I informed you in a former letter[253], these mandibles are used for walking as well as feeding: they are parallel to each other, and are neither formed for cutting nor grinding like the mandibles of other insects, but merely detach particles of food by digging into it and tearing the fibres asunder. In this operation they are probably assisted by an acutely triangular dart-like instrument of a horny substance, which in some species (Musca vomitoria) is placed between the two. In others this part is wanting. Some Dipterous larvæ have two similar mandibles, but instead of being parallel, they are placed one above the other; others (Musca domestica and meridiana) have but one such mandible, and some have no perceptible mandible of any kind. The mandibles of the larva of the crane-flies (Tipula), which are transverse and unguiform, do not act against each other, but against two other fixed, internally concave and externally convex, and dentated pieces[254].

Under-jaws (MAXILLÆ). These are a pair of organs, usually of a softer consistence, placed immediately under the upper-jaws; but as they are usually so formed and situated as not to have any action upon each other, it is probable that in general they rather assist in submitting the food to the action of the mandibulæ, than in the comminution of it. In Lepidopterous larvæ they appear to be conical or cylindrical (at least in that of the cossus so admirably figured by Lyonnet[255]), and to consist of two joints; which may, I imagine, be analogous to the upper and lower portions of which the maxillæ of perfect insects usually consist. The last of these joints is surmounted by two smaller jointed palpiform organs. If any part of the maxillæ can act upon each other, it is these organs or palpi; but it is evident they are not calculated for mastication, although they may assist in the retention of the substance to be masticated. In a figure given by Reaumur of the under side of the head of another lepidopterous larva (Erminea Pomonella), the maxillæ consist of a single joint, and appear to be crowned by chelate palpi[256]: a circumstance which is also observable in that of a common species of stag-beetle (Lucanus parallelipipedus), the weevil of the water-hemlock (Lixus paraplecticus[257]), and other insects. In general the maxillæ of larvæ are without the lobe or lobes discoverable in those of most perfect insects, this part being usually represented by a kind of nipple, or palpiform jointed process, strictly analogous to the interior maxillary palpi of the predaceous coleoptera; but in most of the lamellicorn beetles the lobe exists in its proper form[258], as it does likewise in that of the capricorn-beetle before noticed (Callidium violaceum[259]). In the former instance, it is armed with spines or claws; but in the latter it is unarmed, and rounded at the end. In the larva of Cicindela campestris, the base of the maxilla runs in a transverse direction from the mentum, to which, as is usually the case, it is attached. From this at right angles proceeds the lobe, from the outer side of which the feeler emerges; and the inner part terminates in an unguiform joint, ending in two or three bristles. The structure in the larvæ of water-beetles (Dytiscus L.) is different, for they appear to be without maxillæ[260]; but the case really seems to be, that these organs are represented by the first joint of what M. Cuvier calls their palpi[261]; from which proceed the real palpi, the interior one being very short, and consisting only of a single joint. These maxillæ of larvæ were regarded by Reaumur and other writers as parts of the under-lip, on each side of which they are situated; and indeed, as well as those in the perfect insect, they form a part of the same machine, being connected by their base with the mentum, which is part of the labium, but they are clearly analogous to the maxillæ of the imago. They are not to be found in the larvæ of many Dipterous insects, and perhaps in some species belonging to other orders. In some Neuropterous larvæ, as those of the Libellulina MacLeay, the maxillæ are of a substance quite as solid and horny as the mandibles, which in every respect they resemble[262].

Under-lip (LABIUM). Between the two maxillæ in the larvæ of most of the insects under consideration is a part termed by Reaumur the middle division of the under-lip, but which is in fact analogous to the whole of that organ in the imago. This organ varies in shape, being sometimes quadrangular, often conical, &c. Interiorly it is frequently connected with a more fleshy protuberance, called the tongue by Reaumur[263], and supplying the place of the ligula in the perfect insect. On each side of the apex of the under-lip is a minute feeler, and in the middle between these in the Lepidoptera and many others, is a filiform organ, which I shall call the spinneret (Fusulus), through which the larva draws the silken thread employed in fabricating its cocoon, preparatory to assuming the pupa state, and for other purposes[264]. This organ is found only in those larvæ which have the power of spinning silk; that is, in all Lepidoptera, most Hymenoptera, Trichoptera, some Neuroptera, and even a Dipterous insect[265]. This tube, Lyonnet had reason to believe, is composed of longitudinal slips, alternately corneous and membranous, so as to give the insect the power of contracting its diameter, and thus making the thread thicker or smaller. There is only a single orifice at the end, which is cut obliquely, somewhat like a pen, only with less obliquity, and without a point, the opening being below, so as to be conveniently applicable to the bodies on which the larva is placed. Reaumur conceived that this spinneret had two orifices; but Lyonnet ascertained this to be a mistake, the two silk tubes uniting into one before they reach the orifice. From the contractile nature of the sides and the form of the orifice, combined with the power the insect has of moving it in every direction, results the great difference which we see in the breadth and form of the threads, some being seven or eight times as thick as others, some cylindrical, others flat, others channelled, and others of different thickness in different parts[266]. In the larvæ of many Diptera the under-lip is merely a small tubercle, which can be protruded from the insect's mouth by pressure[267].

One of the most remarkable prepensile instruments, in which the art and skill of a DIVINE MECHANICIAN are singularly conspicuous, and which appears to be without a parallel in the insect world, may be seen in the under-lip of the various species of dragon-fly (Libellula L.). In other larvæ this part is usually small and inconspicuous, and serves merely for retaining the food and assisting in its deglutition; but in these it is by far the largest organ of the mouth, which when closed it entirely conceals; and it not only retains but actually seizes the animal's prey, by means of a very singular pair of jaws with which it is furnished. Conceive your under-lip (to have recourse, as Reaumur on another occasion[268], to such comparison,) to be horny instead of fleshy, and to be elongated perpendicularly downwards[269], so as to wrap over your chin and extend to its bottom,--that this elongation is there expanded into a triangular convex plate[270], attached to it by a joint[271], so as to bend upwards again and fold over the face as high as the nose, concealing not only the chin and the first-mentioned elongation, but the mouth and part of the cheeks[272]: conceive, moreover, that to the end of this last-mentioned plate are fixed two other convex ones, so broad as to cover the whole nose and temples[273],--that these can open at pleasure, transversely like a pair of jaws, so as to expose the nose and mouth, and that their inner edges where they meet are cut into numerous sharp teeth or spines, or armed with one or more long and sharp claws[274]:--you will then have as accurate an idea as my powers of description can give, of the strange conformation of the under-lip in the larvæ of the tribes of Libellulina; which conceals the mouth and face precisely as I have supposed a similar construction of your lip would do yours. You will probably admit that your own visage would present an appearance not very engaging while concealed by such a mask; but it would strike still more awe into the spectators, were they to see you first open the two upper jaw-like plates, which would project from each temple like the blinders of a horse; and next, having by means of the joint at your chin let down the whole apparatus and uncovered your face, employ them in seizing any food that presented itself, and conveying it to your mouth. Yet this procedure is that adopted by the larvæ provided with this strange organ. While it is at rest, it applies close to and covers the face. When the insects would make use of it, they unfold it like an arm, catch the prey at which they aim by means of the mandibuliform plates, and then partly refold it so as to hold the prey to the mouth in a convenient position for the operation of the two pairs of jaws with which they are provided. Reaumur once found one of them thus holding and devouring a large tadpole;--a sufficient proof that Swammerdam was greatly deceived in imagining earth to be the food of animals so tremendously armed and fitted for carnivorous purposes. Such an under-lip as I have described is found in the tribe of dragon-flies (Libellulina); varied, however, considerably in its figure in the different genera. In the larva of Libellula Fab., such as Libellula depressa, &c. it is of the shape above described; so exactly resembling a mask, that if Entomologists ever went to masquerades, they could not more effectually relieve the insipidity of such amusements and attract the attention of the demoiselles, than by appearing at the supper table with a mask of this construction, and serving themselves by its assistance. It would be difficult, to be sure, by mechanism to supply the place of the muscles with which in the insect it is amply provided: but Merlin, or his successor, has surmounted greater obstacles. In the larva of the Fabrician Æshnæ (Libellula grandis, &c. L.), this apparatus is not convex but flat: so that, though it equally conceals the face, it does not so accurately resemble a mask; and the jaws at its apex are not convex plates, but rather two single conical teeth[275]. It is, as to its general shape, similarly constructed in Agrion Fab. (L. Virgo, &c. L.); but the first joint is more remarkably elongated, the jaws more precisely resemble jaws than in any of the rest, and are armed with three long, very sharp teeth: between them also there is a lozenge-shaped opening, through which, when the apparatus is closed, is protruded a circular sort of nipple, apparently analogous to the ligula[276]. Libellula ænea, L., which is the type of another tribe (Cordulia Leach), has a mask somewhat different from all the above, the jaws being armed with a moveable claw and an internal tooth[277]. You will admire the wisdom of this admirable contrivance, when you reflect that these larvæ are not fitted to pursue their prey with rapidity, like most predaceous animals; but that they steal upon them, as De Geer observes[278], as a cat does upon a bird, very slowly, and as if they counted their steps; and then, by a sudden evolution of this machine, take them as it were by surprise, when they think themselves safe. De Geer says, it is very difficult for other insects to elude their attacks, and that he has even seen them devour very small fishes[279]. As these animals are found in almost every ditch, you will doubtless lose no time in examining for yourself an instance of so singular a construction.

Feelers (PALPI). In the orders Diptera and Hymenoptera are many larvæ in which these organs have not been certainly discovered; yet Reaumur in that of a common fly (M. meridiana L.) found four retractile nipples[280] which seem analogous to them; and Latreille has observed, that below the mandibles of those of ants are four minute points, two on each side[281]: but in all other larvæ their existence is more clearly ascertained. The maxillary palpi vary in number, many having two on each maxilla and others only one. In the perfect insect the former is one of the distinguishing characters of the predaceous beetles (Entomophagi Latr.), but in the larvæ it is more widely extended; since even in the caterpillars of Lepidoptera the inner lobe of the maxilla which represents this feeler is jointed, which is precisely the case with the beetles just named. Cuvier has observed this circumstance in the larva of the stag-beetle[282]; and it belongs to many other Coleoptera that have only a pair of maxillary palpi in the perfect state. The labial palpi are always two, emerging usually one on each side from the apex of the under-lip. With regard to the form of the palpi, those of the Lepidoptera are mostly conical; in other orders they are sometimes setaceous and sometimes filiform. Their termination is generally simple, but sometimes the last joint is divided. They are for the most part very short, and the labial shorter than the maxillary. The latter never exceed four joints[283], which seems the most natural number; and the former are limited to three. Both vary between these numbers, and one joint. The joints, though commonly simple, are sometimes branched. This is the case with one I met with in considerable numbers upon the Turnip, in October 1808, the second joint of the palpi of which sends forth near the apex an internal branch. In the larva of the Cossus, as Lyonnet informs us[284], the joints of the palpi are retractile, so that the whole of the organ may be nearly withdrawn.

* * * * *

After thus describing the head of larvæ, and its principal organs, we must next say something upon the remainder of the body, or what constitutes the

2. Trunk and Abdomen: which I shall consider under one article. These are composed of several segments or rings, to which the feet and other appendages of the body are fixed. The form of these segments, or that of their vertical section, varies considerably: in many Lepidoptera, the wire-worm, &c., it would be nearly circular; in others a greater or less segment of a circle would represent it; and in some, perhaps, it would consist of two such segments applied together. Their lower surface is generally nearly plane. Their most natural number, without the head and including the anal segment, is twelve: this they seldom exceed, and perhaps never fourteen. The three first segments are those which represent the trunk of the perfect insect, and to which the six anterior legs when present are affixed. In general, they differ from the remaining segments only in being shorter, and in many cases less distinctly characterized; but in Neuropterous larvæ, those of Dytisci, and some other Coleoptera, they are longer than the succeeding ones, and pretty nearly resemble the trunk of the animal in its last state. The surface of the trunk and abdomen will be considered under a subsequent head; I shall not, therefore, describe it here. The conformation of the different segments varies but little, except of the terminal one, or tail, which in different larvæ takes various figures. In most, this part is obtuse and rounded; in others acute or acuminate; in others truncate; and in others emarginate, or with a wider sinus, and with intermediate modifications of shape which it would be endless to particularize. In some, also, it is simple and unarmed; in others beset with horns, spines, radii, and tubercles of different forms, some of which will come under future consideration. The parts connected with the trunk and abdomen which will require separate consideration, are the legs, the spiracles, and various appendages.

Legs. It may be stated generally that the larvæ of the orders Coleoptera, Lepidoptera, and Neuroptera, have legs; and that those of the orders Hymenoptera and Diptera have none. This must be understood, however, with some exceptions. Thus the larvæ of some Coleoptera, as the weevil tribes (Curculio L.) have no legs, unless we may call by that name certain fleshy tubercles besmeared with gluten, which assist them in their motions[285]; while those of Tenthredo and Sirex in the order Hymenoptera are furnished with these organs. At present I know no Dipterous larva that may be said to have real legs, unless we are to regard as such certain tentacula formed upon a different model from the legs of other larvæ[286]. Rösel has, I think, figured a Lepidopterous apode. No Neuropterous one has yet been discovered.

The legs of larvæ are of two kinds; either horny and composed of joints, or fleshy and without joints[287]. The first of these, as I observed in a former letter[288], are the principal instruments of locomotion, and the last are to be regarded chiefly as props and stays by which the animal keeps its long body from trailing, or by which it takes hold of surfaces; while the other legs, or where there are none, the annuli of its body, regulate its motions. The former have been commonly called true legs (pedes veri), because they are persistent, being found in the perfect insect as well as in the larva; and the latter spurious legs (pedes spurii), because they are caducous, being found in the larva only. Instead of these not very appropriate names, I shall employ for the former the simple term legs, and for the latter prolegs (propedes)[289].

The legs, when present, are always in number six, and attached by pairs to the underside of the three first segments of the trunk. They are of a horny substance, and consist usually of the same parts as those of the perfect insect; namely, coxa, trochanter, femur, tibia, and tarsus, suspended to each other by membranous ligaments: these parts are less distinctly marked in some than in others. Thus in the legs of a caterpillar, or the grub of a capricorn-beetle, at first you would think there were only three or four joints besides the claw; but upon a nearer inspection, you would discover at the base of the leg the rudiments of two others[290], in the latter represented indeed by the fleshy protuberance from which the legs emerge. In the larvæ of the predaceous Coleoptera, the hip and trochanter are as conspicuous nearly as in the perfect insect; and the tarsus, which still consists of only a single joint, is armed with two claws[291]. In those of the Neuroptera order, in which all the joints are very conspicuous, the tarsi are jointed, as well as two-clawed[292]. The legs of larvæ are usually shorter than those of the perfect insect, and scarcely differ from each other in shape, for they all gradually decrease in diameter from the base to the apex. This is the most usual conformation of them in Lepidopterous, Hymenopterous, and some Coleopterous larvæ, (those of the capricorn-beetles are very short and minute, so as to be scarcely visible,) in which they are so small as to be concealed by the body of the insect[293]. In Neuropterous larvæ, however, and several Coleoptera, as those of Dytiscus, Staphylinus, Coccinella, &c., they more resemble the legs of the perfect insect, the joints being more elongated, and the femoral one projecting beyond the body[294].

You will find no other than true legs in most Coleopterous, Neuropterous, and Hymenopterous larvæ. But those of the saw-flies (Tenthredo L.), and all caterpillars, have besides a number of prolegs: a few Dipterous larvæ also, are provided with some organs nearly analogous to them. These prolegs are fleshy, commonly conical or cylindrical, and sometimes retractile protuberances, usually attached by pairs to the underside of that part of the body that represents the abdomen of the future fly[295]. They vary in conformation and in number; some having but one, others as many as eighteen.

With regard to their conformation, they may be divided into two principal sections: first, those furnished with terminal claws; and secondly, those deprived of them. Each of which may be divided into smaller sections, founded on the general figure of the prolegs, and arrangement of the claws or hooks.

i. The prolegs of almost all Lepidopterous larvæ are furnished with a set of minute slender horny hooks, crotchets, or claws, of different lengths, somewhat resembling fish-hooks; which either partially or wholly surround the apex like a pallisade. By means of these claws, of which there are from forty to sixty in each proleg, a short and a long one arranged alternately, the insect is enabled to cling to smooth surfaces, to grasp the smallest twigs to which the legs could not possibly adhere: a circumstance which the flexible nature of the prolegs greatly facilitates[296]. Claws nearly similar are found on the prolegs of some Dipterous larvæ[297], but not in any of those of the other orders. These last, however, are seldom either so numerous, or arranged in the same manner, as in caterpillars. When the sole of the foot is open, the claws with which it is more or less surrounded are turned outwards, and are in a situation to lay hold of any surface; but when the animal wishes to let go its hold, it begins to draw in the skin of the sole, and in proportion as this is retracted, the claws turn their points inwards, so as not to impede its motion[298].

The prolegs with claws may be further divided into four different kinds.

1. In the larvæ of the great majority of butterflies and moths they assume the form of a truncated cone, the lower and smaller end of which is expanded into a semicircular or subtriangular plate, having the inner half of its circumference beset with the claws above mentioned; and, from its great power of dilating and contracting, admirably adapted for performing the offices of a foot. Jungius calls these legs pedes elephantini[299]; and the term is not altogether inapplicable, since they exhibit considerable resemblance to the clumsy but accommodating leg and foot of the gigantic animal he alludes to.

2. The larvæ of many minute moths, particularly of the Fabrician genera Tortrix and Tinea--those which live in convoluted leaves, the interior of fruits, &c., as well as the Cossus, and some other large moths,--have their prolegs of a form not very unlike those of the preceding class, but shorter, and without any terminal expansion; the apex, moreover, is wholly, instead of half, surrounded with claws[300]; the additional provision of which, together with a centrical kind of nipple capable of being protruded or retracted, in some measure, though imperfectly, supplies the place of the more flexible plate-like expansion present in the first class.

3. The third class is composed of a very few Lepidopterous larvæ which have their prolegs very thick and conical at the base, but afterwards remarkably slender, long, and cylindrical, so as exactly to assume the shape of a wooden leg[301]. These, as in the first class, are expanded at the end into a flat plate: but this is wholly circular, is surrounded with claws, and has also in the middle a retractile nipple, as in the preceding class. In Cossus, at least in an American species (Cossus Robiniæ), described by Professor Peck[302], the anal prolegs have the claws only on their exterior half.

4. The remaining description of unguiferous prolegs, if they may not rather be deemed a kind of tentacula, are those of certain Diptera, provided with no true legs; which differ from the three preceding classes, either in their shape, or the arrangement of their claws. In one kind of those remarkable larvæ, which from their long respiratory anal tubes Reaumur denominates "rat-tailed," that of Elophilus pendulus, there are fourteen of these prolegs, affixed by pairs to the ventral segments, the twelve posterior ones of which are subconical, and truncate at the apex, which is surrounded with two circles of very minute claws, those of the inner being much more numerous and shorter than those of the exterior circle; while the anterior pair terminate in a flat expansion, and in shape almost exactly resemble those of a mole[303]. The prolegs of the larvæ of a kind of gnat called by De Geer Tipula amphibia, and of Syrphus mystaceus F., (Musca plumata De Geer,) are nearly of a similar construction, but in the last are armed with three claws only[304]. Long moveable claws also distinguish the singular prolegs before described[305] of another gnat (Tanypus maculatus Meig., Tipula De Geer). The case-worms (Trichoptera K.) and some others, have two prolegs at the anus, each furnished with a single claw[306].

ii. The prolegs deprived of claws are found in the larva of the Hymenopterous tribe of saw-flies (Tenthredo L.), in those of some Lepidoptera (Hepialus F. &c.), and in some few Coleopterous and Dipterous genera. Those of the former are of the shape of a truncated cone, and resemble the second class of unguiculate prolegs, except in the defect of claws. In the latter they are a mere retractile nipple-like protuberance, in some species so small as scarcely to be perceptible. In all they aid in progressive motion; but it is by laying hold of surfaces, and so enabling the body more readily to push itself forward by annular contraction and dilatation, and not by taking steps, of which all prolegs are incapable: to assist in this purpose the protuberance sometimes secretes a gluten[307], which supplies the place of claws. Some larvæ have the power of voluntarily dilating certain portions of the underside of their body, so as to assume nearly the shape and to perform the functions of prolegs. In a Coleopterous (?) subcortical one from Brazil, before alluded to, there are four round and nearly flat areas in each ventral segment of the abdomen, but the last very little raised above the surface, and rough, somewhat like a file; and besides these, the base of the anal segment has ten of these little rough spaces, but of a different shape, being nearly linear, placed in a double series, five on each side. Doubtless these may be regarded as a kind of prolegs, which enable the animal to push itself along between the bark and the wood[308].

In considering, in the next place, the number and situation of the prolegs, it will contribute to distinctness to advert to these circumstances as they occur in the different orders furnished with these organs.

To begin with the Lepidoptera.--Lepidopterous larvæ have either ten, eight, six, or two prolegs, seldom more[309], and never fewer. Of these, with a very few exceptions, two are attached to the last or anal, and the rest, when present, to one or more of the sixth, seventh, eighth, and ninth segments of the body: none are ever found on the fourth, fifth, tenth, or eleventh segments.

1. Where ten prolegs are present, as is the case in by far the greatest proportion of Lepidopterous larvæ, there is constantly an anal pair, and a pair on each of the four intermediate segments just mentioned.

2. In caterpillars, which like those of a few species of the genera Sphinx, Pyralis, and of the Bombycidæ, &c. have eight legs, they are placed in three different ways. In those which have an anal pair, the remaining six are in some fixed to the sixth, seventh, and eighth; in others, to the seventh, eighth, and ninth segments. In those which, like Cerura Vinula, and several other species of the same family, have no anal prolegs; the whole eight emerge from the sixth, seventh, eighth, and ninth segments.

3. The Hemigeometers, as Noctua Gamma, &c. have only six legs: namely, an anal pair, and two ventral ones, situated on the eighth and ninth segments.

4. The larvæ of the Geometers (Geometræ F.) have but four prolegs; of which two are anal, and two spring from the ninth segment. It should be observed, however, that the larvæ of Hemigeometers, and even of some of those that have ten prolegs, where the four anterior ones are much shorter than the rest, move in the same way as the Geometers. This even prevails in a few where these organs are all of equal length.

5. Many of the larvæ of Tinea L. which live in the interior of fruits, seeds, &c., have but one pair of prolegs, which are attached to the anal segment.

6. The larvæ of Haworth's genus Apoda (Hepialus Testudo and Asellus F.), remarkable for their slug-like shape and appearance, move by the aid of two lateral longitudinal pustule-like protuberances, which leave a trace of a gummy slime in their course.

Hymenoptera.--The larvæ of the different tribes of Tenthredo L., almost the only Hymenopterous insects in which prolegs are present, have a variable number of these organs; some sixteen, as the saw-fly of the willow (T. lutea L.), and this is the most numerous tribe of them, including the modern genera, Cimbex F., Pterophorus, &c. Others have fourteen, as that of the cherry (T. cerasi L.); and many others with only nine joints to their antennæ. A third class have only twelve, as that of the rose (T. Rosæ L.), but this contains but few species. The last class contains those that have no prolegs at all, but only the six horny ones appended to the trunk. Of this tribe, the caterpillars of which have a very different aspect from the preceding, are those of the genus Lyda F. (T. crythrocephala L.)[310]. Two of the prolegs are anal, and the rest intermediate, and none are furnished with claws. This circumstance, in conjunction with the greater number of prolegs, except in the case of Lyda, will always serve as a mark to distinguish these fausses chenilles, as the French call the larvæ of saw-flies, from true caterpillars. The dorsal prolegs of a species of Cynips described by Reaumur have been before noticed.

Coleoptera.--The larvæ of insects of this order are so little known or attended to, that no very accurate generalization of them in this respect is practicable. Many of them, in addition to their six horny legs, have a proleg at the anus; which in many cases appears to be the last segment of the abdomen, forming an obtuse angle with the remainder of it, so as to support that part of the body, and prevent it from trailing; and in some instances, as in Chrysomela Populi, a common beetle, secreting a slimy matter to fix itself[311]. In the larvæ of Staphylinidæ this proleg is very long and cylindrical; in that of Cicindela it is shorter, and in shape a truncated cone rather compressed; it is very short, also, in those of the Silphæ that I have seen. In the wire-worm (Elater Segetum) it is a minute retractile tubercle, placed in a nearly semicircular space, shut in by the last dorsal segment, which becomes also ventral at the anus. This space is in fact the last ventral segment. This seems characteristic of the genus[312]. From the underside of the body of the common meal-worm (Tenebrio Molitor), at the junction of the two last segments, when the animal walks, there issues a fleshy part, furnished below with two rather hard, long, and moveable pediform pieces, which the animal uses in walking[313]. In the larva of another beetle, whose ravages have been before noticed, under the name of the cadelle[314] (Trogosita mauritanica), a pair of prolegs are said to be found under the anal segment; and in that of the bloody-nose beetle (Timarcha tenebricosa), that segment is bifid. That of the weevil of the common water-hemlock (Lixus paraplecticus F.) exhibits a singular anomaly: prolegs occupy the usual station of the true legs, being attached to the three segments representing the trunk[315]. This insect, however, does not appear to use them in moving. A pair in each of the twelve segments of the body are found in the grub of another weevil (Hypera Rumicis Germ.), the nine last pair being the shortest, which all assist the insect in walking[316]. But the greatest number of prolegs is to be found in the Brazil subcortical larva lately mentioned. Besides the six horny legs of the trunk, this remarkable animal has four prolegs on each of the seven intermediate abdominal segments, and five on each side of the base of the last, making the whole number of prolegs, if so they may be called, amount to forty-four: a far greater number than is to be found in any larva at present known. When I wrote to you upon the motions of insects, I informed you that some larvæ moved by means of legs upon their back[317], but I was not then aware that any were furnished with them both on the back and the belly at the same time. By the kindness of Mr. Joseph Sparshall of Norwich, a very ardent and indefatigable entomologist, I am in possession of the larva of Rhagium fasciatum, a timber-feeding beetle. This animal on the ten intermediate segments of the underside of the body, which in the centre form a fleshy protuberance, has on it a double series of rasps, as it were, consisting each of two rows of oblique oblong prominences; and on the seven intermediate dorsal segments there are also in the centre seven rasps of three or four rows each, of similar prominences: so that this animal at the same time can push itself along both by dorsal and ventral prolegs. It is worthy of observation, that a pair of these rasps is between the second and third pair of true legs.

Diptera.--The larva of a little gnat, Tipula stercoraria De Geer[318] (Chironomus Meig.?), drags itself along by the assistance of a single tubercle, placed on the underside of the first segment of the body, which the animal has the power of lengthening or contracting[319]. That of another beautiful Chironomus (C. plumosus), remarkable for the feathered antennæ of the male[320], has two short prolegs, or pediform but not retractile tentacula in the same situation[321]. Others, as that of Tanypus maculatus, &c. have two pairs, one attached to the anal and the other to the first segment[322]. Tipula amphibia De Geer in this state has ten prolegs, placed by pairs on the fourth, fifth, eighth, ninth, and tenth dorsal segments[323]; and Scæva Pyrastri F., one of the aphidivorous flies, has not fewer than forty-two, arranged in a sextuple series, seven in each row[324].

It may not be useless to close this long description of the legs of larvæ with a tabular view of them, founded chiefly upon these organs; which afford very obvious marks of distinction.

I. Larvæ without legs.

i. With a corneous head of determinate shape (coleopterous and hymenopterous apods--Culicidæ, some Tipulidæ, &c. amongst the Diptera).

ii. With a membranaceous head of indeterminate shape (Muscidæ, Syrphidæ, and other Diptera).

II. Larvæ with legs.

i. With legs only, and with or without an anal proleg (Neuroptera, and many Coleoptera).

1. Joints short and conical (Elater, Cerambycidæ, &c.).

2. Joints long and subfiliform (Staphylinus, Coccinella, Cicindela, &c.).

ii. Prolegs only (many Tipulidæ, and some subcutaneous Lepidopterous larvæ, &c.).

iii. Both legs and prolegs (Lepidoptera, Tenthredinidæ, and some Coleoptera).

1. Without claws (Tenthredinidæ, &c.).

2. With claws (Lepidoptera, &c.).

I should next say something upon the spiracles, or breathing-pores, or any other external apparatus for the purpose of respiration, in larvæ; but I think it will be best to reserve the consideration of these for a subsequent Letter. We will therefore conclude this detailed description of their parts in their first state, with some account of their other.

iii. Appendages. The generality of larvæ have no other external organs than those already described; but in several of them we observe various kinds of retractile ones and others--protuberances--horn-like processes--rays, &c.; which, though not properly coming either under any of the above parts, or under the clothing of these animals, yet require to be noticed. Upon these I shall now enlarge a little.

You must have observed upon the back of the last segment but one of the caterpillar of the silk-worm a horn-like process, rising at first nearly perpendicularly, and then bending forward. A similar horn, though confined in the genus Bombyx to the silk-worm and a few others, if we may believe Madame Merian, who, however, often makes great mistakes, is found in the beautiful caterpillar of one of the largest and finest moths that we know (Erebus Strix[325]), the glory of the Noctuidæ, and in most of those of the hawk-moths (Sphinx F.) [S. Porcellus, Vitis, and a few others excepted; in some of which, as S. Labruscæ, &c., this anal horn is replaced by a gibbosity, and in others, as S. Œnotheræ, by a callous eye-like plate[326]] in the same situation, but much longer[327], and commonly curving backwards over the tail[328]. Sometimes, however, as in S. ocellata and S. Stellatarum, it is perfectly straight. These organs towards the apex are horny, and often end in a sharp point; nearer the base they are fleshy. They are without any true joint[329], yet the insect can elevate or depress them at pleasure. Under a lens, they usually appear covered with spinous eminences, arranged like scales. The use of these horns is quite unknown: Goedart fancies that they secrete a potent poison, and are intended as instruments of defence; but both suppositions are altogether unfounded. It has been remarked, that the body of those caterpillars which have these horns, is firmer, and yields less to the touch than that of those which have no such appendages[330]. The larva of a small timber-devouring beetle (Lymexylon dermestoides F.) has, like the above caterpillars, a long horn, and in the same situation: it has also a singular protuberance on the first segment[331]. Upon some other caterpillars, as in Bombyx Stigma F., a singular pair of horn-like appendages arises from the back of the second segment of the body, excluding the head. In a tawny-coloured one from Georgia, with a transverse row of short black spines on each segment, these horns are half an inch long, black, covered with spinous eminences, rather thickest at the base, and terminate in a little knob. They appear to articulate with the body at the lower extremity. I have another species, black, with narrow longitudinal yellow stripes, in which these horns are of equal thickness at base and apex, but with the same terminal knob. Danais Archippus has a pair of tentacula at the head, and another pair, but shorter, at the tail; and D. Gylippus has, besides these, two in the middle of the body[332].

We are equally ignorant of the use of the upright horn found upon the back of the fourth segment in the larva of some moths (Noctua Psi, and tridens F.) which is of a construction quite different from that of those last described. It is cylindrical, slightly thinner at the apex, which is obtuse, fleshy, incapable of motion, of a black colour, and about two lines long. On the same segment, also, in the case-worms (Trichoptera K.) are three fleshy conical eminences, which the animal can inflate or depress, so that they sometimes totally disappear, and then in an instant swell out again. When retracted, they form a tunnel-shaped cavity, varying in depth[333]. Reaumur conjectured that these eminences were connected with respiration, and one circumstance seems in favour of this conjecture, that this segment has not the respiratory threads observable in the subsequent ones. Latreille mentions certain fleshy naked eminences placed upon the ninth and tenth segments of some hairy caterpillars, which, like those just mentioned, the animal can elevate more or less. They are often little cones; but when it would shorten them, the summit is drawn in, and a tunnel appears where before there was a pyramid[334].

In a former Letter I gave you a short account of the remarkable Y-shaped, as it should seem, scent-organs (Osmateria) of the beautiful caterpillar of the swallow-tailed butterfly (Papilio Machaon L.), and others of the Equites[335]; I will now speak of them more fully. That found in the former is situated at the anterior margin at the back of the first segment, close to the head, from which at first view it seems to proceed. At the bottom it is simple, but divides towards the middle, like the letter Y, into two forks, of a fleshy substance[336], which it can lengthen, as a snail does its horns, to five times their ordinary extent, or retract them within the stalk, so as wholly to conceal them. Sometimes it protrudes one fork, keeping the other retracted; and often withdraws the whole apparatus for hours together under the skin, and its place is only marked by two tawny-coloured dots, so that an ordinary spectator would not suspect the existence of such an instrument[337]. Unfortunately this larva is rare in this country, so that I can scarcely flatter you with the hope of seeing this curious organ in a living specimen[338], unless you choose to import a parcel of its eggs from the south of Europe, where it is common. This you will think rather a wild proposition; but why should not Entomologists import the eggs of rare insects, as well as botanists the seeds of rare plants? But if you will be satisfied with the dissection of a dead specimen, I have several, done by the ingenious Mr. Abbott of Georgia, in which this part is well exhibited[339].

Another small caterpillar, as it should seem, of a geometer, prepared by the same gentleman, exhibits a pair of similar horns on the fifth and sixth segments: in these the common base from which the fork proceeds is very short and wide, and each branch grows gradually more slender from the base to the apex, where it is involute. Whether these are retractile, or whether they correspond with those of P. Machaon in their nature and use, cannot be ascertained from a dead specimen: as they belong to a larva of a quite different tribe of Lepidoptera, the probability is, that they essentially differ. Two globose retractile vesicles issue from the ninth and tenth segments of those of Arctia chrysorrhea, &c.[340]

A great number of Lepidopterous larvæ, particularly those which are smooth and of a moderate size, have between the under-lip and fore-legs a slender transverse opening, containing a teat-like protuberance of the same construction as the furcate horn of the caterpillar of the beautiful mountain-butterfly, Parnassius Apollo; and, like that, can either be wholly retracted and concealed, or by pressure be extended to the length of one of the legs. In some larvæ this part is of a subhemispherical figure, generally single, but sometimes double. It is commonly, however, more slender and conical; and when of this shape, it is sometimes quadruple[341]. The use of this part is not very clearly known: some have supposed it to be a second spinneret, and to be of use in fabricating the cocoon; but it is more probable that it secretes some other kind of fluid, and is connected with defence.

The singular organ in a similar situation, evidently for that purpose, with which the puss-moth endeavours to annoy its assailants, has been described in a former Letter, to which I refer you[342]. Bonnet, who was the first that discovered this organ, ascertained that it might be cut off without injury to either larva or imago. He also remarked in a caterpillar found in the wild succory (Cichorium Intybus) another short, black, needle-shaped organ between the conical part just described and the under-lip[343]. De Geer mentions a remarkable fleshy horn-like style, which issues from the lower side of the first segment, between the head and the legs of the case-worms (Trichoptera): he does not describe it as retractile, or it might be regarded as analogous to those of Lepidoptera similarly situated, that I have just noticed[344]. In that of the emperor-moth (Saturnia Pavonia), there are perforated tubercles, which when the animal is molested spirt forth a transparent fluid[345].

The horn-like appendage of the puss-moth (Cerura Vinula) is situated at the tail of the insect, and is composed of two distinct cylindrical diverging branches, each about four lines long, not united at the base. Each of these is hollow, and includes a smaller cylindrical piece, which can be protruded at pleasure, and withdrawn again, as a pencil within its case; or, rather, as the horns of a snail. The two outer horns are tolerably firm, moveable at their base, and beset with black spines; the interior tentacula are fleshy, moveable in every direction, and in full-grown larvæ of a rose colour. The animal seldom protrudes them, unless in some way disturbed; and frequently it approximates the two outer cases so closely that they resemble a single horn. It appears to use these inner horns, when protruded, as a kind of whip to drive away the flies, especially the Ichneumons, that alight upon its body. When touched in any place, it will unsheath one of them, and sometimes both, and with them strike the place where it is incommoded[346]. A similar organ is found in some other Bombycidæ, as B. Tau and Furcula F. Reaumur mentions a caterpillar that to this kind of tail added the resemblance of two ears, or two cylindrical bodies, terminating in a point, which emerged from the first segment behind the head[347]. In another observed by the same author, the legs were replaced by a single horn, but which did not appear to send forth an internal one: from the back of its fourth segment also emerged a single conical or pyramidal fleshy eminence or cleft, terminating in two points[348]. Some of the tropical butterflies also, as may be seen in the figures of Madame Merian, have two diverging anal horns instead of anal prolegs; but it does not appear that they incase tentacula[349]. Wherever these caudal horns are found, the above prolegs are wanting[350]. Two conical anal horns also distinguish the caterpillar of one of the moths called Prominents, Notodonta camelina; but these are not terminal, but on the back of the last segment but one[351]. In that of another British moth, N. ziczac F., there are three dorsal prominences, one near the anus, and two more in the middle[352]. Some Geometers (G. fuliginosa, &c.) have two erect horns on the eleventh segment, and others (G. syringaria, &c.) two recurved ones on the eighth[353]. I must not here omit to mention the curious hooks emerging from two tubercles on the back of the eighth segment of the ferocious larva of that beautiful tiger-beetle, the Cicindela campestris L., not uncommon on warm sunny banks. This animal with incessant labour, as we are informed by M. Desmarets, digs a cylindrical burrow, to the enormous depth, the size of the animal considered, of eighteen inches. To effect this, it carries out small masses of earth upon its large concave head; and having often occasion to rest in ascending this height, by means of these hooks[354] it fixes itself to the sides of its burrow, and, having finally arrived at its mouth, casts off its burthen. When these insects lie in wait for their prey, their head, probably in conjunction with the first segment of the body, accurately stops the mouth of the burrow, so as to form an exact level with the surrounding soil; and thus careless insects, walking over it without perceiving the snare, are seized in a moment and devoured[355].

Another kind of appendage, which is found in some larvæ, is the organ employed by them to carry the excrement; with which, instead of letting it fall to the ground, they form a kind of umbrella to shelter and probably conceal them. All the tortoise-beetles (Cassida L.) have instruments for this purpose, as well as an Indian genus (Imatidium Latr.) very nearly related to them. This instrument is a kind of fork, half as long as the body, consisting of two branches, growing gradually smaller from the base to the summit, where they terminate in a very fine point, of a substance rather horny, and attached to the body near the anal orifice. They are armed on the outside with short spines, from the base for about a third of their length. When this fork, as it usually is, is laid parallel to the back, with its points towards the head, the anal aperture points the same way. When the animal walks, the fork points the other way, and is in the same line with the body, and the anus assumes a prone position[356].

The larvæ of a genus of flies (Volucella Geoffr.) remarkable for inhabiting the nests of humble bees, are distinguished on their upper side by six long, diverging, pointed, membranous radii; placed in a semicircle round the anus[357]: what the particular use of these organs may be, has not been conjectured. Another in my collection has only four upper radii, but below the anus are two fleshy filiform tentacula. One of a Tipulidan described by Reaumur, has also four upper teeth; but instead of two subanal tentacula, has six[358]. The singular larva of another of this tribe (Chironomus plumosus) has on the two last segments four long, fleshy, filiform, flexible tentacula, often interlaced with each other; which, according to the same illustrious author, are used by the animal to fix its caudal extremity, like the geometers, that the other end may be at liberty. Besides these organs round the anus, it has also four other oval ones, of uncertain use: not to mention the two prolegs, which M. Latreille thinks are air-tubes[359]. Jointed anal organs are observable in other larvæ: those in that of a saw-fly described by De Geer (Lyda F.) consist of three joints[360]; in that of Hister cadaverinus, a carnivorous beetle, of two[361]. The larva as well as the pupa and imago of Ephemera is furnished with three long diverging multiarticulate tails, which are probably useful as a kind of rudder to assist and direct their motions. That of the smaller dragon flies (Agrion F.) is furnished with three long vertical laminæ, by moving which, as fish do their tails, from side to side, the animal makes its way in the water[362]. That singular one, also, with a hooked head, figured by Reaumur, has a single swimming lamina, or fin, shaped like a fan, and placed in a vertical position under the tail[363].

The whole circumference of the body in some coleopterous larvæ,--for instance, in that of the tortoise-beetle lately mentioned,--is surrounded with appendages like rays. These are sometimes simple, rough with very short spinous points[364]; but I have a dipterous larva, in which these radii themselves are beautifully pinnated by a fringe of longish spines on each side. Reaumur has described the grub of a beetle, the genus of which is uncertain, and which feeds upon the larva of Aleyrodes Proletella, whose body is margined on each side by eight triangular fleshy mammular processes, terminating each in a bristle, which give it a remarkable aspect[365]. The curious scent-organs with which the larva of Chrysomela Populi is fringed have been before fully described; and therefore I shall only mention them here[366].

In the larvæ of the lace-winged flies (Hemerobius), and ant-lions (Myrmeleon), the anus is furnished with a small fleshy retractile cylinder, from which proceeds the silken thread that forms the cocoon inclosing the pupa[367]. Providence has many different ways of performing the same operation. From the structure of the oral organs of these animals, the silk could not conveniently be furnished by the mouth; the Allwise Creator has therefore instructed and fitted them to render it by a spinneret at the other extremity of the body.

The respiratory anal appendages of many Dipterous larvæ will be fully described in a subsequent Letter: I shall therefore now only further observe upon this subject, that although there is seldom any alteration in the form of these appendages &c. in the same species, the caterpillars of two moths (Cerura Vinula and Attacus Tau), however, are exceptions. The former, when young, has two hairy projecting ear-like protuberances, which it entirely loses, as I have myself observed, before it assumes the pupa; and the latter, in like manner, after its third change of skin, is deprived of its bent thorn-like points which attend it when young[368]. It is remarkable that these last larvæ, when just excluded from the egg, are also entirely destitute of these appendages; they soon, however, appear, from slight elevations which mark their situation, and rapidly acquire their usual form[369]. Changes of a similar kind, hitherto unobserved, may probably take place in other species.

iii. Figure. I am next to consider the general figure or shape of larvæ. All of them, with but few exceptions[370], agree in having a body more or less constricted at intervals into a series of rings or segments; usually in number, twelve; often nearly equal in length, but sometimes in this respect very dissimilar[371]. The general outline or shape of the body is extremely various: most frequently it approaches to cylindrical, as in most of the caterpillars of Lepidoptera, and of the Hymenopterous tribe of saw-flies (Tenthredo L.). The next most common figure is that more or less oblong or oval one, sometimes approaching to conical, found in many of the larvæ usually called grubs; such as those of the weevil (Curculio L.) and of the capricorn (Cerambyx L.), and other coleopterous tribes; of bees, and all Hymenopterous insects but the saw-flies; and also of a large number of flies (Diptera). In some the figure approaches to fusiform, as in most of the moths of the Fabrician genus Lithosia. In others, as in those of the water-beetles (Dytiscus, &c.), it approaches to an obovate shape, being widest towards the head, and terminating in a point at the anus. In others, again, it is linear; an example of which is that of Staphylinus. Some are convex, and others gibbous, above, and flat underneath; as those of Silpha, Chrysomela and many other beetles. Others are flat, both above and below, and depressed like a leaf; a remarkable instance of which has been before noticed[372]. Some are very long, as those of most Lepidoptera; others very short, as that of the ant-lion (Myrmeleon). Many other peculiarities of form in individuals might be instanced; but a dry enumeration of these would be of no great use to you. They can only be advantageously learned by the study of good figures, and by watching the actual metamorphosis of the singularly-formed larvæ that you meet with.

Instead, therefore, of any further specification of individual forms, I shall now endeavour to give you, as far as my own knowledge of them and the information I can collect from other sources will enable me, a larger and more general view of the kinds of larvæ; for analytical inquiries lose half their value and importance unless we proceed to apply them synthetically, by forming, if possible, into groups the objects with which we are individually acquainted.

Partial attempts at a synthetical arrangement with regard to the larvæ of Lepidoptera and the saw-flies (Tenthredo L.) have been made both by Reaumur and De Geer. M. Latreille also has recently given a Tableau méthodique et général of articulated animals furnished with jointed legs, considered in their first state[373]. The former of these is chiefly founded upon the number of the prolegs, and the latter upon the metamorphosis, prolegs, habits, head, and parts of the mouth, without any other notice of the configuration. Mr. Wm. MacLeay, who, though young in years, is old in science and critical acumen, has started a perfectly new hypothesis upon this subject. In the progress of his inquiries into the natural arrangement of animals, particularly of insects in the Linnean sense, he has been the first to observe, that the relation which organized objects bear to each other is of two kinds; one of real affinity, and the other only of analogy, or resemblance. This important distinction, upon which I shall enlarge in a future Letter, when I come to treat of Systems of Entomology, he has applied, in a way quite original, to larvæ in general, but more particularly to those of the Coleoptera order. For the basis of his system he assumes a relation of analogy between the larvæ of Insects that in the progress of their metamorphosis assume wings, and those that do not, which form his class Ametabola, so that the prototypes of the former shall be found amongst the latter[374]. But though Mr. MacLeay appears to consider the analogy between these two as primary, he extends it in a secondary sense to the Crustacea, at least in several instances[375]. Upon this occasion he very judiciously remarks, that "in terming larvæ Chilognathiformes or Chilopodiformes, it is not meant that they are Scolopendræ or Iuli, or even near to them in affinity; but only that they are so constructed that certain analogical circumstances attending them strongly remind us of these Ametabola[376]." This remark you will bear in mind while I am treating of this subject. It should seem from another part of the same paragraph, that the comparison which our learned Physiologist recommends, is between the young of the Ametabola and the larvæ of the corresponding groups of Coleoptera. This must be understood to refer chiefly to the young of the Chilopoda and Chilognatha, since they approach nearer to them in that state, having then only six legs; but the rest of the Ametabola should certainly be brought to this comparison in their adult state: and even the two former orders in that state more strongly resemble numerous coleopterous larvæ, than when they are young and much shorter. I before called your attention to the remarkable circumstance that contrasts very many larvæ of Hexapod insects that become winged in their perfect state with adult Myriapoda: namely, that in one the progress to this state is by losing their prolegs and shortening their body; while in the other, the reverse of this takes place, numerous prolegs and additional segments being gained before they arrive at maturity[377]. As the multiplication of organs is a sign of imperfection, it may be affirmed of the former of these tribes, that their progress is towards greater perfection; while that of the other may be called a degradation. As larvæ may be regarded as a stepping-stone by which approach is made from the apterous to the winged tribes of Insects, it seems most consistent with general analogy that each should connect with the other in that state in which the resemblance is greatest. Now the Myriapoda resemble larvæ, as we have just seen, most when in their adult state; therefore the comparison should be between larvæ and adult Myriapoda.

Mr. MacLeay divides coleopterous larvæ into five tribes thus characterized:--

1. A carnivorous hexapod larva, with an elongate linear flattened body, having a large head armed with two sharp falciform mandibles, and furnished with six granular eyes on each side. This kind he denominates Chilopodiform, as having for its type in the Ametabola, Scolopendra L. The examples he gives are Carabus and Dytiscus.

2. A herbivorous hexapod larva, with a long and almost cylindrical body, so fashioned that the posterior extremity being curved under the breast, the animal when at rest necessarily lies like an IULUS on its side. This tribe he denominates Chilognathiform, from Iulus L. His examples are, the larvæ of Petalocerous insects, as Scarabæus L., Lucanus L. &c.

3. An apod larva, having scarcely the rudiments of antennæ, but which is furnished instead of feet with fat fleshy tubercles; which, when continued along the back and belly, give the animal a facility of moving in whatever way it may be placed. These he denominates Vermiform, from certain of the Vermes intestina and Mollusca of Linné which he has associated with his Annulosa[378]. His examples are, Curculio L. and Cerambyx L.

4. A hexapod and distinctly antenniferous larva, with a subovate rather conical body, of which the second segment is longer and of a different form from the others, so as to give the appearance of a thorax. His denomination for these is Anopluriform, from Pediculus L., forming Dr. Leach's Anoplura. His examples are, Coccinella and Chrysomela L.

5. A hexapod antenniferous larva of an oblong form, having like the former vestiges of a thorax, besides two or more articulated or inarticulated setaceous or corneous appendages to the last segment of the abdomen. This tribe he calls Thysanuriform, from Lepisma and Podura L., forming M. Latreille's order Thysanura. His example is Meloe with a note of interrogation[379].

The system here stated, of naming and characterizing larvæ from the resemblance and analogy, in many cases very striking, that they bear to the apterous tribes, is a very happy and original one, and does its author great credit; yet I think in some instances, as I shall soon have occasion to point out to you, the application of it is not so happy as the first idea. But this is always the case when a new law of nature is discovered; the proper application of it is gradually developed, and it does not at all detract from the merit of the first discoverer, that all the bearings of such law do not strike him as it were intuitively.

Having, however, got the vantage-ground afforded by this discovery of my friend, let us see if by standing upon it we cannot get a tolerable generalization of the larvæ of all orders of insects that undergo a metamorphosis. But first I must observe, that as in the perfect animals, so in their larvæ, the different groups are connected by certain transition species, exhibiting characters common to two or more of them; and likewise that in many cases, which you will see as we proceed, the analogy is as strong or stronger between them and the Crustacea (and in a few instances Arachnida, and even Mollusca) than the Ametabola. My denominations, therefore, will be taken from those tribes where the analogy appears to me the most striking, and not from the Ametabola alone.

I shall begin by drawing up for you a list of the Primary forms that I seem to have observed, and their characters; and then going through the orders, shall give you the examples of each, with such observations upon them as the case may require.

Primary Forms of Larvæ.

APTERA. ARACHNIDA. CRUSTACEA.

ANOPLURIFORM. ARANEIDIFORM. ISOPODIFORM. THYSANURIFORM. ONISCIFORM. CHILOPODIFORM. IDOTEIFORM. CHILOGNATHIFORM. AMPHIPODIFORM. STOMAPODIFORM. MOLLUSCA. ANNELIDA. DECAPODIFORM. BRANCHIOPODIFORM. LIMACIFORM. VERMIFORM.

Characters.

1. Anopluriform. Carnivorous; hexapod; antenniferous: with a shortish oblong depressed body, and distinct thoracic shield. Example: Psocus, Coccinella, most Hemiptera[380].

2. Thysanuriform. Polyphagous; hexapod; antenniferous: body with segments of trunk distinctly marked; anus often furnished with setæ or mucro. Ex. Meloe[381]? Thrips, Aphis.

3. Chilopodiform. Carnivorous; subhexapod; antenniferous: body depressed, elongate, linear, with falcate acute mandibles, a distinct thoracic shield, and an anal proleg. Ex. Cicindela[382]? Carabus L.

4. Chilognathiform. Herbivorous; body subcylindrical, elongate, linear; no thoracic shield; often many prolegs, sometimes a retractile one, and sometimes none.--Ex. Elater, Petalocera, most Lepidoptera, Tenthredo L.[383]

5. Vermiform. Polyphagous; apod or hexapod: with very short legs; antennæ nearly obsolete; body fleshy, plicate, with sides often plicato-papillose; no distinct thoracic shield. Ex. Curculio L., Cerambyx L., Musca L., and many other Diptera[384].

6. Araneidiform. Carnivorous; hexapod: body very short; mandibles long, suctorious; animal lying in wait for its prey in a pitfall it has prepared; motion retrogressive. Ex. Myrmeleon L.[385] Cicindela?

7. Isopodiform. Saprophagous; hexapod; antenniferous, with longer antennæ: body oblong; thoracic shield distinct; anus styliferous or laminiferous. Ex. Blatta L. Silpha L.?

8. Onisciform. Herbivorous; polypod; antenniferous: body short, oblong, depressed, margined. Ex. Erycina, Lycæna, in the Lepidoptera, and some species of Tenthredo L.[386]

9. Idoteiform. Subcortical; hexapod; antennæ obsolete: body much depressed, with the last segment elongate, terminating in three or more mucros. Ex. Larva from Brazil. Perfect insect at present unknown.

I have placed this larva, which was described above[387], amongst crustaceous forms, because of the remarkable resemblance which the last segment of the body bears to that of the Idoteidæ; but I do it with considerable hesitation, since in other respects its type seems to be in the Ametabola. In its want of antennæ, very short legs, and ventral asperities, it resembles some of the Vermiform larvæ; in its small head, distinct thoracic shield, and oblong shape, it approaches the Anopluriform; and in its very depressed body, but not at all in other respects, the Chilopodiform. At any rate, it appears of a primary Type.

10. Læmodipodiform. Herbivorous; hexapod; antenniferous, with long antennæ: body elongate, subcylindrical; second segment of the trunk the longest; anterior pair of legs distant from the other two. Ex. Phasma.

11. Amphipodiform. Herbivorous; hexapod; antenniferous, with long antennæ: body shortish, compressed, saltatorious. Ex. Gryllus L.[388]

12. Stomapodiform. Carnivorous or saprophagous; hexapod; antenniferous, with long antennæ: body elongate, subdepressed, with raptorious hands, and abdomen wider than the trunk; in aquatic species furnished with lateral gills. Ex. Mantis, Ephemera? Sialis?

13. Decapodiform. Carnivorous; hexapod; antenniferous: body elongate, narrow, convex, compressed, tapering towards the tail; tail with natatorious laminæ. Ex. Dytiscus L., Agrion F.[389]

14. Branchiopodiform. Carnivorous?; aquatic; apod; antenniferous: head distinct: body transparent, flexile, furnished with a respiratory tube just above the tail. Ex. Culex[390].

15. Limaciform. Herbivorous; apod, or with very short legs: body ovate or obovate, slimy. Ex. Apoda Haw., _Tenthredo Cerasi_ L.

The above are the principal forms that appear to me Primary (though some doubt may rest upon the ninth and tenth); and probably others will hereafter be discovered, since at present our knowledge of the larvæ of most of the Orders is very limited. And now having given you this generalization of them, as far as they are known to me, I shall next, in a slight survey of those of the different orders, lay before you what I have further to observe upon this subject.

Coleoptera. The Anopluriform coleopterous larvæ, according to Mr. W. MacLeay's view of them, include both those of Coccinella L., Chrysomela L., and Cassida L.; but this appears to me to admit of further consideration. With regard to the two former--those of Coccinella are carnivorous, those of Chrysomela herbivorous; the first is also usually more flat and depressed. As to the latter, Cassida[391], it seems to me to belong to a peculiar type, distinguished not only by its radiated margin, but by the remarkable deflected anal fork on which it carries its excrement. At present I know no analogous form amongst the apterous tribes; I must therefore leave this without a denomination. Perhaps the larva of Hispa or Alurnus, when known, will throw light upon this subject. The larva of Endomychus agrees with that of Coccinella.

There are very few known larvæ that approach to a true Thysanuriform type in this order: that most celebrated is the one supposed to belong to Meloe; but the claim of this to be so considered, is, as we have seen, rather dubious. Should this point at last be satisfactorily ascertained, it will probably carry with it the whole tribe of vesicatory beetles. But even this animal in its general structure is anopluriform: the only circumstance that gives it any analogy to the Thysanura being its anal setæ. Mr. William MacLeay is inclined to regard some of the larvæ of the Malacodermi Latr., but which of them he does not state, as probably belonging to the tribe in question[392]. Those of Lampyris and of Telephorus, as described and figured by De Geer[393], appear to me intermediate between the Anopluriform and Chilopodiform Types: they have no anal setiform or styliform appendages, their mandibulæ are falcate, and their habits seem carnivorous.

Examples of Chilopodiform coleopterous larvæ are more numerous. Of this description are those of Gyrinus, Cicindela, Carabus, and Staphylinus. That of the first, indeed, appears to be the most perfectly Scolopendriform of any yet known; yet the gills or respiratory laminæ, a pair of which issues from each abdominal segment, and two pair from the last[394], prove that there is no slight analogy between it, and indeed many other aquatic larvæ, and the Stomapoda amongst the Crustacea. A remarkable instance of analogy with the Decapoda of the same Class is presented by the larva of Dytiscus, &c. which Mr. MacLeay considers as Chilopodiform, but which exhibits no other resemblance to Scolopendræ than in its predaceous habits and threatening aspect. Its convex, compressed, tapering body, terminating in setæ or laminæ, is certainly much more like that of a shrimp or a prawn; to which the older Entomologists thought it was akin[395], and after which they named it. As Mr. MacLeay's object was, to take all his forms from the Ametabola, perhaps these larvæ will best fall in with his Chilopodiform type; though in the general form of their body they most represent a section (Lepisma L.) of the Thysanura.

Chilognathiform forms are equally numerous in the Coleoptera with the preceding. The wire-worm, or larva of Elater Segetis, as to shape best represents the full-grown Iulus[396], and those of the Petalocera (Scarabæus L., Lucanus L.) the young one.

The most abundant of all forms in this order, is, I think, the Vermiform, upon which I have nothing further to remark.

With regard to Crustaceous forms in Coleoptera, besides the Decapodiform just noticed, I possess two specimens of larvæ of Silphidæ which seem to exhibit a considerable analogy with the Isopodous Crustacea, one rather convex and the other flatter, so as to give the idea of an Armadillo and of an Oniscus.

Strepsiptera. Larva Vermiform.

Dermaptera. Larva Thysanuriform. Type Podura or Sminthurus.

Orthoptera. Mr. MacLeay considers the larvæ of this Order as primarily Thysanuriform[397], though he allows the resemblance between them and Amphipoda to be particularly striking[398]. For my own part, their prototypes appear to me to be in the Crustacea, and their analogical relations to the Thysanura much more distant. I trust this will appear to you the reverse of dubious in a progress through the Crustaceous Orders. I begin with the Isopoda. Take the larva of a Blatta, and place it between a Lepisma, or Machilis, and an Oniscus, or Porcellio; you will find that in shape and width, and the form of its anal styles, it resembles the latter much more than it does the former, with which it possesses scarcely any character in common, except its multiarticulate antennæ. It is remarkable, that amongst the Blattidæ we meet with species that represent both the Oniscidæ and Armadillo or Glomeris[399], the latter being more convex than the former. In their habits the Blattæ certainly agree with Lepisma; and Dumeril, who thought the latter and Podura subject to a metamorphosis, imagined they were related[400].

The Spectres of Stoll (Phasma F.) are so strikingly analogous to another crustaceous tribe, the Læmodipoda, particularly the genus Caprella, that Montagu gave one species the Trivial name of Phasma[401]. The jumping Amphipodiform Crustacea are represented extremely well by Gryllus L., and the Stomapodiform, particularly Squilla Mantis, by Mantis. The resemblance in this last instance is so very striking, that it cannot escape the eye of the least intelligent observer. Orthopterous insects may perhaps one day be discovered analogous to the two other crustaceous orders, the Decapods and Branchiopods; but at present I know of none of that description.

Hemiptera. The larvæ of this order, which in general resemble the perfect insect, except that they have no wings, seem most commonly to belong to the Anopluriform type[402]; but the Aphides, Chermes, and Thrips may, I think, be regarded as more analogous to the genera Podura and Sminthurus in the Thysanura[403]. I have some suspicion that the Nepidæ, Naucoris, and the remipedes, Notonecta, Sigara, &c. may find their prototypes amongst the Crustacea; but my confined knowledge of the latter does not enable me to point to any individual genera or tribes that they may be presumed to represent.

Neuroptera. As the kinds of larvæ of the different tribes composing this order, as it now stands, are very various, it is to be expected that the analogical forms they represent are equally so. The Libellulina MacLeay (whose metamorphosis that gentleman has denominated subsemicomplete, a term warranted by their losing in their perfect state the mask before described[404]) in their oral organs, particularly by their galeate maxilla and distinct ligula[405], have some relation to the Orthoptera, the prototypes of whose larvæ we have found amongst the Crustacea: probably, therefore, those of the tribe in question lurk in that class; a suspicion that receives strong confirmation from the larva of Agrion[406], which in its tapering body and anal natatorious laminæ represents a shrimp. The larvæ of that very peculiar and distinct tribe, the Ephemerina, appear to be intermediate between the Stomapodiform and Thysanuriform types. Their natatory respiratory abdominal laminæ seem copied from the former, and their anal diverging setæ from the latter[407]. The Myrmeleonina, as well in their general form as in their motions and habits, present a most singular analogy with the tribe of spiders, as does also in some respect that of Cicindela. With regard to Panorpa, which Mr. MacLeay remarks is related to Myrmeleon[408], and is a most ferocious insect[409], as its larva has not yet been discovered, nothing certain respecting its analogical form can be asserted; but should it, like the male fly, represent the scorpion, both orders of Arachnida will have their representatives in the class we are considering. The Corydalina, as far as the larva of Hemerobius instructs us, is Chilopodiform, but with a tendency to the Araneidiform Type. The Ametabola also furnish the prototype of the next tribe, the Termitina, which, as is evident both from Psocus and Termes, are perfectly Anopluriform. The Sialina, or Plicipennes of Latreille, excluding Trichoptera Kirby, appear to me to be intermediate between the Chilopodiform and Stomapodiform Types, and not without some relation to the Thysanuriform. Their pediform, jointed, respiratory abdominal appendages, their head and falcate mandibles, seem copied from the first tribe. The same appendages considered as organs of respiration, and their taper forks, are moulded upon the plan of the Stomapodiform Crustacea, and the long seta which terminates the abdomen is upon the Thysanuriform plan[410].

Trichoptera. The larvæ of this order appear also to be constructed upon a double plan. The respiratory threads observable in both the upper and under sides of the abdomen connect it with the Stomapoda, and its cylindrical elongate body with Chilognathiform types in the Lepidoptera[411].

Lepidoptera. The great majority of larvæ in this order are Chilognathiform, but there are exceptions to this remark. Those of the Geometræ recede from this type, both in their motions and the distance and number of their legs. In both these respects they represent the Læmodipoda in the Crustacea[412]. Other caterpillars are Onisciform; and a third sort seem to leave the Annulose type, and imitate that of the Mollusca, and one is figured by Madame Merian[413] which appears to tend even to the Chilopodiform type.

Hymenoptera. In this order the larvæ of the saw-flies, Tenthredo L., are in general Chilognathiform, though some are Onisciform, others Limaciform, and those of Lyda F. (Cephaleia Jur.) and Sirex[414] have a Vermiform tendency, and are a stepping-stone to those of the rest of the order, which are all Vermiform and apods.

Diptera. The majority of this order may be set down as Vermiform, though it is not improbable that some of them bear an analogy to animals that appear far removed from the Annulosa. Thus, the larva of Stratyomis Chameleon seems to exhibit no small resemblance to some of the Polypi vaginati in the Acrita subkingdom of Mr. W. MacLeay[415]. That of Culex and some others is constructed on a quite different type from the rest, and seems to possess some analogy to the Branchiopod Crustacea.

Though some of these analogies are more striking than others, yet in almost all that I have stated there is that kind of resemblance that could not be the result of what is called mere chance; and Mr. MacLeay, by first pointing out this plan of the All-wise Creator, and by laying down the doctrine of analogies in general, as distinguished from affinities in the animal kingdom, has furnished the believer with a new argument against those attacks of the infidel, that would render null those proofs of the wisdom and goodness of the Author of nature with which the animal and vegetable creation furnish us; by affirming most absurdly, and under the most stultifying blindness of mind, that the creatures were in a manner their own creators, their wants under local circumstances stimulating them to efforts that in a long course of years produced all the different forms and organizations that are now to be found in our globe. The affinities and close connexion of beings with each other, so that the ascent from low to high is usually by the most gentle gradations, is the circumstance on which they build this strange and impious theory. But the fact, that certain animals of one tribe were created with a view to certain animals of another, so as to present a striking aspect of correspondence, parallel almost with that of type and antitype, without any real affinity or approximation;--this triumphantly proves a Power above and without them, who has associated them not only in a complex chain of affinities, but has caused them to represent and figure each other, even when evidently far removed, so as to give a mutual correspondence and harmony to the whole, which could be produced only by a Being infinite in power and wisdom, who made all things after a general preconceived plan and system.

iv. We are now to consider the clothing with which larvæ are furnished. Many are quite naked, and smooth or rough only with granular elevations or tubercles orderly arranged; but a very considerable number, especially of the Lepidoptera order, are clothed with hair or bristles of different kinds, in greater or less abundance, and arranged in different modes; and a proportion still smaller have their skin beset with spines or a mixture of spines and hairs. Lyonnet found that the hairs of the caterpillar of the great goat-moth (Cossus ligniperda) were hollow, though not to the apex: probably this is the case with those of other larvæ, as well as with their spines. In this instance they were set, he observes, in a corneous ring, or very short cylinder, elevated a little above the skin. The hair passes through this ring, and appears to be rooted in a soft integument, which clothes the skin within, and upon which the nerves form a reticular tissue, some of which he thinks he has even seen enter the root of the hairs, which perhaps are organs of touch[416].

Of the pilose larvæ, some, like most of those of the smaller moths (Geometra, Tortrix, Pyralis, &c.), have merely a few scattered short hairs, scarcely perceptible except through a lens: others (Odenesis potatoria, Lasiocampa Rubi) are covered with down more or less thick: in others (Eriogaster lanestris, Lasiocampa Neustria) the hair is slenderer, and more like wool; the body of two species which I purchased from the collection of Mr. Francillon is covered with woolly hairs, so long as to give them the appearance of a shock-dog; and Madam Merian has figured a similar one, which she could not bring to the perfect state[417]. The hairs of many Bombycidæ, known commonly by the name of hairy caterpillars, as Arctia erminea, &c. are stiffer, resembling bristles; sometimes, as in Arctia chrysorhea, mixed with shorter ones. The hairs either spring immediately from the skin (Noctua Aceris, leporina), or, as is more general, proceed only from certain tubercular elevations, usually subhemispherical, but sometimes conical; of which a number varying from four to twelve are found on each segment of different species. They seem to issue from these tubercles, as little diverging streams from the rose of a watering-pot. In both cases, they form a coating usually so dense as to conceal the body, but sometimes more thinly set, and admitting the skin to be seen more or less between them. In a caterpillar of the beautiful Arctia ocularia, the hairs are set upon tubercles alternately nearer the anterior and posterior margin of each segment, so as to form a dense band, the rest being naked; and in the lovely green and black one of Saturnia Pavonia, each tubercle bears but six hairs, diverging like a star, the central one being the longest and capitate, so that the chief part of the body appears naked. This diverging position of the hairs is most common in the thick-clothed larvæ also, but many have them placed differently: thus, in those of Callimorpha Caja and Arctia villica[418] they are all directed towards the tail, like the quills of a porcupine: in some others the anterior ones point towards the head: in that of Eriogaster Quercus half of the tuft of hairs of each tubercle is directed downwards, the other half upwards: in that of Arctia Salicis all the hairs point downwards, so that the belly is thickly covered, while the back is bare. Another variation is, that the hairs of half the tubercle are sometimes very long, while those of the other half are very short, and even of a different colour[419]. In the larva of Tussuck moths (Laria pudibunda, fascelina, &c.) the hairs are collected into tufts of a singular appearance, those on the intermediate segments of the back being quite level at the top, so as to resemble so many brushes; while those on the first and last segments are longer, and composed of feathered hairs converging to a point at their extremity, like a common camel-hair-pencil[420]. This last mode of arrangement prevails also in the larva of Noctua Aceris; but in this the pencils are shorter, exactly wedge-shaped, and distinguished by another particularity, that of springing directly from the skin, and not from a tubercle. This is also the case with the large caterpillars of Odenesis potatoria, which has a double row of short bundles of black hairs on the back, intermixed with larger ones: at each end of the body is a pencil of converging hairs, and the sides are spotted with bundles of white ones, which with longer tawny ones are bent downwards, so as to cover the sides of the creature[421]. Some have the anterior aigrettes disposed like the arms of a cross, of which the body of the caterpillar is the stem[422]. But not only is there considerable variety in the general arrangement of the hairs that clothe our little larvæ, the hairs themselves differ much in their kind and structure, of which I will now, before I proceed to consider spines, give you some account. Several of them are feathered like the plumes of a bird: this is the case with those of Morpho Idomeneus, on each segment of the body of which are three blue tubercles, like so many little turquois beads, from each of which proceeds a long black plume[423]. Other hairs terminate in a club; those of the larva of Noctua Alni, a specimen of which I possess taken in England, are flat and incrassated at the apex, something like the antennæ of some Sphingidæ. Mad. Merian has figured the caterpillar of another moth which feeds upon the Papaw-tree (Carica Papaya) with similar hairs[424]. But the most remarkable larva for the shape of its hairs is that of Anthrenus Musæorum, the little pest of our cabinets, which I noticed in a former letter[425]. All the hairs of its body are rough with minute points; but those of six diverging long tufts or aigrettes, laid obliquely on the anal extremity of the body, which the animal when alarmed erects as a porcupine does its quills, are of a most singular structure: every hair is composed of a series of little conical pieces, placed end to end, the point of which is directed towards the origin of each hair, which is terminated at the other extremity by a long and large conical mass, resembling somewhat the head of a pike[426].

Besides the one lately mentioned, other caterpillars are rendered striking by the brilliant colour of the tubercles from which their hairs emerge. A remarkable instance of this is the thick large caterpillar of a Bombyx, which feeds upon the Psidium pyriferum, or white Guava, figured by Madame Merian. This caterpillar, which is white, with transverse black stripes, and which has two singular long converging curved bunches of hairs near the tail, is splendidly adorned on each side with fifty red tubercles, shining like coral, from which proceed six or seven long diverging hairs. Leeuwenhoeck took these tubercles for eyes[427]. Another figured by the same lady, who mistakes it, with her usual inaccuracy, for the larva of a Lygæus F., and which seems by her description to be between the onisciform and limaciform types, has the apparently fleshy mamillæ that project from its sides and back crowned with little hairy red globes, which give the animal a most singular and unique appearance[428]. Having thus described some of the principal modes in which the All-wise Creator has decked and defended these creatures with hairs, I shall next give you a short account of the spines with which he has armed others. The spinous larvæ are principally lepidopterous, and more particularly conspicuous in some tribes of the genus Papilio L., though some saw-flies and Diptera are also distinguished by them. Vanessa Io[429], Atalanta and Urtica, Argynnis Paphia, Urania Leilus, and many other Butterflies, &c. are clothed with long sharp points, which claim the denomination of spines, rather than that of hairs or bristles; being horny and hard, and so stiff at the point as readily to pierce the skin. Those of the last-mentioned species, Madame Merian says, are as stiff as iron-wire[430]. They are sometimes entirely simple, and look like spikes rather than spines, as in the caterpillar of Nymphalis Amphinome and Morpho Menelaus[431]; but ordinarily they are beset with hairs, or more commonly with shorter spines, which often give them the appearance of plumes, as in Urania Leilus just mentioned: sometimes these lateral spines are so long as to have the appearance of a branch of a tree; this is strikingly the case with a small caterpillar which Captain Hancock brought from Brazil; its body is so thickly planted with spines of this description, that it absolutely wears the appearance of a forest or thicket in miniature. A singular circumstance attends the spines of this species: in many cases a smaller and very slender hair-like spine issues from them, resembling a sting; and this accounts for an observation of Abbott's, that many American caterpillars sting like a nettle, raising little white blisters on the skin when accidentally or slightly touched[432]. Lewin has described the caterpillar of a moth found in New Holland, which he names Bombyx vulnerans, that, like these Americans, has also the power of wounding, but in a different way. It darts out, he says, when alarmed by the approach of any thing, from as many knobs or protuberances in its back eight bunches of little stings, with which it inflicts a very painful and venomous wound[433]. The caterpillar of Papilio Protesilaus F., if Madame Merian's account and figure of it are correct, has its body armed with hairy spines, the extreme point of which is surmounted by a star-shaped appendage[434]. Those of a few saw-flies (Tenthredo Pruni L.), and another figured by Reaumur[435], are covered with a little forest of spines without lateral branches, but divided into a fork at the apex. Some spines are merely rough, with very short points, as those round the head, which give so terrific an appearance to the caterpillar of the Bombyx regalis, of some proceedings of which I gave you an account in one of my former letters[436].

I must now say something upon the arrangement of these spines. Though in a few instances so thickly set as entirely to conceal the body of the animal, as in the case of the Brazil one lately mentioned, yet generally speaking, even when they are most numerous, they permit the skin to be distinctly seen. Their arrangement is various, though always orderly: in the majority they are planted singly, but in some caterpillars in bundles. In that of Saturnia Io, on each segment there are six bundles of longish, quill-shaped, sharp, slender, diverging spines, which also appear to sheath aculei. Madame Merian has figured this larva, or one very near it, as the grub of a Euglossa[437], with which, though she affirms she traced it to the fly, it can have no connection. With regard to number, some larvæ have only four spines on each segment; others five, others again six, and others seven, or even eight: they are planted on the sides and back only, never on the belly. They are often more numerous on the intermediate than on the anterior and posterior segments; but sometimes the reverse of this takes place; in that of Attacus Erythrinæ only the head and tail are armed with spines, the rest of the body being without any[438]; and in that of Morpho Teucer there is only a single spine on the four intermediate segments[439]. They are usually all nearly of equal length; but in some cases those of the head and tail are much longer than the rest, and remarkably so in the caterpillar of Urania Leilus, also beautifully plumose, and gracefully waved[440]. Those in the second and third segments are much longer than any of the rest in that of Bombyx regalis; which circumstance gives it the terrific appearance lately alluded to. In the family to which Argynnis Paphia belongs, the larva is adorned with two on the back of the first segment twice as long as the rest, and resembling at first sight two antennæ.

The spines, as well as the hairs of the new skin, are concealed under the old one, and not incased in its spines; but Bonnet ascertained, that if cut off very closely, the larva sometimes died in consequence, whilst no such result followed a similar operation on hairy larvæ. We learn from Reaumur[441], that some spinous larvæ of saw-flies (Tenthredo L.) lose their spines at the last change of their skin; and from Madame Merian, that that of Attacus Erythrinæ before mentioned loses also at the same period the six tremendous black spikes that arm its black and yellow larvæ. The grubs of ants that are destined to pass the winter in the larva state are hairy, but are not so in summer[442]. The spines found in the grubs of some gad-flies (Œstrus L.) are of a different kind from those above described, being very minute triangular flat plates, arranged in different and contrary directions[443], and serving the insect merely to change its place and fix itself[444].

Two other kinds of clothing, if so they may be called, neither coming under the description of hairs nor spines, are found in some other larvæ, not only amongst the Lepidoptera, but also in some of the other orders. Nymphalis Populi and others of the same family have larvæ furnished on the back of each segment with cylindricoconical processes of a fleshy substance, obtuse at the apex and surrounded with capitate hairs. In that of N. Sybilla, which has on each segment two fleshy protuberances, they are bifurcate or trifurcate, and also encircled at the base with a hairy tuft[445]. Others, as those of Melitæa Artemis, Cynthia, &c. have each segment beset on the back with from seven to nine fleshy, pubescent, wedge-shaped protuberances; two larger ones projecting over the head. Under this head, too, may be noticed, the glutinous secretion which clothes the grub of Cionus Scrophulariæ, a little weevil; and of Tenthredo Cerasi L. a saw-fly, and that waxy or powdery substance which transpires through the skin of the larvæ of several Aphides, Chermes, Cocci, Hylotoma ovata F., &c. The Aphis, whose extensive ravages of our apple-trees (A. lanata) were before described to you[446], is covered and quite concealed by this kind of substance, so that the crevices in the bark which they inhabit look as if they were filled, not with animals, but with cotton. The insect, also, that forms those curious galls produced upon the spruce fir, and which imitate its cones (Chermes Abietis L., Aphis De Geer) secretes a similar substance. In these and other cases of the same kind, this matter seems to be, if I may so speak, wire-drawn through numerous pores in certain oval plates in the skin, more depressed than the rest of the back, arranged regularly upon the segments, and exhibiting minute tuberosities. When young, these animals have more of this secretion than when more advanced: it then hangs from their anal extremity in locks[447].

But the insects most remarkable for a covering of this nature are those Coccidæ of which Bosc has made a genus under the name of Dorthesia. De Geer is the first author that notices them, and has given a description and figure of one species under the name of Coccus floccosus[448]. It was discovered by Modeer upon some sere fir-leaves in a thick bed of moss. Panzer has figured a second found upon Geranium sanguineum, which from the figure appears distinct from De Geer's, under the name of Coccus dubius[449]. Fabricius regards this as synonymous with the Dorthesia characias of Bosc, inhabiting Euphorbia characias in South Europe[450]. Olivier found a species upon the bramble[451]. I once took one, which appears to differ in some respects from the preceding species, upon Melampyrum cristatum, and our indefatigable friend Mr. Sheppard has sent me another, on what plant found I do not remember, which does not agree with any that I have mentioned. The body of the animals of this genus is covered by a number of cottony or waxy laminæ which partly cover each other, and are arranged usually in a triple series: in De Geer's figure the series appears quadruple, the lateral ones being placed obliquely. The anterior one in my specimen covered the head, and they are all canaliculate. Above the anus are four diverging ones: the whole are of the most dazzling whiteness. When these laminæ are removed, the body appears divided into segments.

With respect to those larvæ which imitate slugs by the viscid covering that besmears them and issues from their pores, we learn from Professor Peck that this exudation takes place as soon as they are hatched; that the animal retains its humidity although exposed to the fiercest heat of the sun, and that at the last moult the skin becomes quite clean, and free from all viscidity[452]. It is probable that the other limaciform larvæ are similarly circumstanced. Madame Merian has figured an onisciform one, the legs of which, she says, are covered with a viscid skin: this produced a Noctua. Those of Papilio Anchises also are slimy, and adhere to each other[453].

v. Amongst other qualities which attach to larvæ, we must not omit to say something concerning their Colour. For though those which live in darkness, in the earth, in wood, in fruits, &c. are, with few exceptions[454], of an uniform whitish colour, yet such as are exposed to the influence of the light are usually adorned with a vast variety of tints, sometimes the most vivid that can be imagined. That the white colour of the former may be attributed to the absence of light is proved by an experiment of M. Dorthes, who having forced some to live under glasses, exposed to the light, found that they gradually became brown[455]. To attempt any classification of coloured larvæ would be in vain, since they are tinged with almost every possible shade that can be conceived, of many of which it would be difficult to find examples elsewhere; and infinitely diversified as to the arrangement and figure of their multiform markings and spots. A few general remarks, therefore, are all that you will expect on this head. Many are of one uniform colour; while a variety of tints, very different, and very vivid and distinct, ornament others. Sometimes they are distributed in longitudinal rays or bands, at others in transverse ones. Sometimes they are waved or spotted, regularly or irregularly; at others they are sprinkled in dots, or minute streaks, in every possible way. Various larvæ are of the colour of the plant on which they feed, whence they are with difficulty discovered by their enemies. Thus, a large proportion of Lepidoptera are green of different shades, sometimes beautifully contrasted with black bands; a circumstance which renders the caterpillars of two of our finest insects of this order as lovely as the fly: I mean that of Papilio Machaon and Saturnia Pavonia. Very frequently the larvæ of quite different species resemble each other so exactly, in colour as well as shape, as scarcely to be distinguishable: this sometimes takes place even where they belong to different genera, as in those of Bombyx versicolor a moth, and Smerinthus Populi a hawk-moth. And it sometimes happens, very fortunately for distinguishing allied species, that where the perfect insects very nearly resemble each other, the larvæ are altogether dissimilar. Thus, the female of Pieris Rapæ is so much like the same sex of Pieris Brassicæ, that it might be taken for a variety of it, did not the green caterpillar of the one, and the spotted one of the other, evince the complete distinction of these butterflies. Noctua Lactuca, N. umbratica, and several other species of the same tribe, which includes N. Absinthii, Verbasci, Chamomillæ, Abrotani, are so extremely alike, that the most practised eye can scarcely discover a shade of difference between them, though their larvæ in colour and markings are constantly distinct[456]. The markings of species belonging to the same family are usually different; but in some cases the latter may be prejudged from the former. The larvæ of many of the genus Sphinx L., for example, have their sides marked by oblique streaks running from the back in a direction towards the head; and by this last circumstance they are distinguished from those of Bombyx versicolor, Attacus Tau, and others of the same tribe, which have also lateral oblique striæ, but running from the back towards the tail[457]. The colours of individual larvæ of the same species are usually alike, but in Sphinx Elpenor and some others they vary exceedingly. Many, like those of Lasiocampa Rubi, Saturnia minor, &c., are of one colour when first disclosed, and assume others quite different in riper age. Just previously to changing their skin, the tints of most larvæ become as dull and obscure, as they are fresh and vivid when the change has fully taken place; and in some instances the new skin is quite differently marked from the old one. This is remarkably the case with the last skin of some of the larvæ of the genus Tenthredo L., which is entirely different from all the preceding ones. As people when they advance far in years usually become more simple in their dress than when they were young, so the larvæ in question change an agreeably variegated skin for one of a uniform and less brilliant colour[458]. Madame Merian has observed with respect to Attacus Erythrinæ, that its caterpillar is at first yellowish, with nine black striæ on each side: when arrived at one third of its size, they become orange; the striæ are obliterated, and in their place a round black spot appears on each of the eight intermediate segments[459]. Mr. Sheppard has remarked to me, that the skin of that of Sphinx Ligustri, after being under ground four days, was changed from a vivid green to a dull red. Very rarely, however, it becomes of a more brilliant hue just before entering the pupa state: thus, that of another hawk-moth (Smerinthus Tiliæ) changes to a bright violet; and the yellow hairs of that of Laria pudibunda then become of a lovely rose colour. And here I may observe, that the hairs and spines also, of larvæ, vary greatly in colour. They are to be met with brown, black, red, yellow, violet, white, &c. De Geer found, that in the larva of Cimbex nitens the two sides of the body were of a different colour, the left being of a deep green, whilst the right side and the rest of the body were paler[460]; but as he saw only a single individual, this was probably an accidental circumstance. Though the caterpillars, as I lately said, of one of the most beautiful butterflies and moths that inhabit Britain contend with the perfect insect in loveliness, yet in general no judgement can be formed of the beauty of the future fly from the colour of the larva; and the young Aurelian must not flatter himself always with the hope, because the caterpillar excites admiration by its colours and their arrangement, that the butterfly or moth it is to produce will do the same; nor ought he to despise and overlook a sombre or plain-coloured individual of the former, under the idea that it will produce one equally plain of the latter, for it often happens that the splendid caterpillar gives a plain butterfly or moth, and vice versâ. De Geer, however, gives us two instances of conformity between the colours of the caterpillar and those of the future moth; the one is that of the common currant-moth (Phalæna G. grossulariata L.), the caterpillar of which is white, ornamented with several black spots varying in size. At the two extremities it is yellowish, with a longitudinal ray of the same colour on each side, the head and legs being black. These colours are all to be found in the fly, the ground of its wings being white ornamented with many black spots of different sizes. Its upper wings are traversed by a yellowish band; and towards their base is a spot of the same colour. Its body is yellowish, with black spots; but the head and legs are black[461]. The other is that of a green caterpillar, which gives a green moth, figured by Reaumur (Pyralis prasinaria Fab.)[462]. Sometimes, also, the sex of the future perfect insect may be predicted from the colour it exhibits in its first state: thus, the brown caterpillars of Noctua Pronuba produce males, and the green ones females[463]. The sexes, also, of N. exoleta and Persicariæ differ in that state.

vi. To the full account of the Food of insects given in a former letter[464], which had reference chiefly to their larva state, it is only necessary in this place to add a few particulars not there noticed. Many larvæ when first excluded, as those of Pieris Cratægi, &c. devour the shells of the eggs from which they have proceeded[465]; and others (Cerura Vinula, Sphinx Euphorbiæ, Noctua Verbasci), though their usual food is of a vegetable nature, eat with great apparent satisfaction the skins which they cast from time to time, not leaving even the horny legs. This strange repast seems even a stimulating dainty, which speedily restores them to vigour, after the painful operation by which they are supplied with it. Under this head it will not be out of place to mention, that some larvæ of insects, which feed only on the juices of animals, or the nectar and ambrosia of flowers, have no anal passage, and of course no feces. This is said to be the case with the grubs of bees, wasps, the larvæ of Myrmeleon, &c.[466]

vii. You will require no stimulus to induce you to attend to the subject I am next going to enter upon,--the Moulting, namely, of Larvæ; or their changes of skin. This, indeed, is a subject so replete with interest, and which so fully displays the power, wisdom, and goodness of the Creator, affording at the same time such large occasion for nice investigation, that a pious and inquisitive mind like yours cannot but be taken with it. In the higher orders of animals, though the hairs of quadrupeds and the feathers of birds are in many cases annually renewed, the change, or scaling and increment of the skin, is gradual and imperceptible; no simultaneous rejection of it, in which it is stripped off by the animal itself like a worn shirt, being observable, till you descend in the scale to the Serpent tribe[467], which at certain periods disengage themselves from their old integument, and start forth with that new and deadly beauty so finely described by the Mantuan bard:--

"So from his den, the winter slept away, Shoots forth the burnished snake in open day; Who, fed with every poison of the plain, Sheds his old spoils and shines in youth again: Proud of his golden scales rolls tow'ring on, And darts his forky tongue[468], and glitters in the sun." PITT.

In these the new skin, I imagine, is formed under the old from the rete mucosum; but in insects, as I formerly stated[469], since the time of Swammerdam it has generally been believed by entomologists, that the larva includes a series of cases or envelopes, one within the other, containing in the centre the germe of the future perfect insect, whose development and final exclusion take place only when these cases have been successively cast off. This hypothesis, as was explained to you on a former occasion[470], has been controverted by a late writer, Dr. Herold; who affirms that the skins of caterpillars are also successively produced out of the rete mucosum. I have however, I hope, satisfied you that the old system is most consonant to nature and probability: but as we are now to enter at large upon the Moults of insects, it will not be without use if I add a few additional reasons which seem to me still further to prove the correctness of Swammerdam's system, as far as it relates to that subject. With regard to the mere formation of the skin from the rete mucosum, were this the whole question few would hesitate to adopt the sentiments of M. Herold; but when we come to consider further--that the number of moults of individuals of the same species is always the same, and that it varies in different species, and takes place at certain periods,--we begin to suspect that something more than the mere formation of a new skin upon an old one being cast is to be accounted for; and that the law which prescribes its own definite number of skins to each species, must begin to act in the primordial formation of the larva. Again, the hairs observable in the higher animals do not take their origin from the epidermis solely, but are planted below it in the rete mucosum, or deeper[471]; so that the change of skin does not affect them; but in the larvæ of insects they are a continuation of that integument, since, when the moult takes place, they always remain on the rejected skin[472]: this is the case, also, even with spines. If you shave a caterpillar ready to change its skin, either partially or generally, you will find that the parts in the new skin that correspond with those that are denuded, are equally hairy with those that were not[473]; and if you pay attention to the new-clad animal, you will find further, that the hairs never grow after a moult. From hence it follows, that the hairs have their place and take their whole growth between the new skin and the old[474]. Whether the spines, simple or compound, lately described to you, that arm some larvæ are similarly circumstanced, seems not as yet to have been ascertained; but as the spinous ones of certain Tenthredines L. and Lepidoptera at their last moult have no spines, the presumption is, that, whether incased or not, they are mere appendages of the skin on which they appear. A new set of hairs, therefore, and probably of spines in spinous larvæ, accompanying each skin, and these varying very much in size, composition, &c. though a new membrane may be admitted to be formed from an action in the rete mucosum without a pre-existent germe of it, it seems not easy to conceive how these hairs and spines can spring up and grow there, each according to a certain law, without existing previously as a kind of corculum or punctum saliens; and that the germes of the tubercles, in which the hairs are so generally planted, according to a certain arrangement and in a given number, should also pre-exist, seems most consonant to reason. These and the several skins may all co-exist in their primordial germes, and remain beyond the discovery of our highest powers of assisted vision, till a certain period when they may first enter the range of the microscope-aided eye. It does not therefore follow, because these primordia semina rerum are not discoverable, that therefore they may not exist. Our faculties and organs are too limited and of too little power to enable us to see the essences of being.

Upon the supposition that the hypothesis of Swammerdam is the true one, we may imagine that the envelope that lies within all the rest is that which covers the insect in its pupa state. Above this are placed several others, which successively become external integuments. These changes or casting of the skin in larvæ, analogous, as before observed, to that of serpents, are familiar to every breeder of silk-worms, in which four such changes occur: the first at the end of about twelve days from its birth, and the three next each at the end of half that time from the moulting which preceded it. With some exceptions[475], similar changes of the skin take place in all larvæ, not however in the same number and at the same periods. Most indeed undergo this operation only three or four times; but there are some that moult oftener, from five up to eight (Arctia villica), nine (Callimorpha Dominula), or even ten times; for so often, M. Cuvier informs us, the caterpillar of the tiger-moth (Callimorpha Caja) casts its exuviæ. It has been observed that the caterpillars of the day-flying Lepidoptera (Papilio L.) usually change only three times, while those of the night-flying ones (Phalæna L.) change four[476]. The periods that intervene between each change depend upon the length of the insect's existence in the larva state. In those which live only a few weeks or months, they are from eight to twenty days; while in those that live more than a year, as the cockchafer, &c. they are probably proportionably longer: though we know very little with regard to the moult of any insects besides the Lepidoptera.

A day or two previously to each change of its skin, the larva ceases eating altogether; it becomes languid and feeble, its beautiful colours fade, and it seeks for a retreat in which it can undergo this important and sometimes dangerous and even fatal operation in security. Here, either fixing itself by its legs to the surface on which it rests, or, as is the case with many caterpillars, by its prolegs, to a slight web spun for this purpose, it turns and twists its body in various directions, and alternately swells and contracts its different segments. The object of these motions and contortions seems to be, to separate the exterior skin, now become dry and rigid, from the new one just below it. After continuing these operations for some hours, resting at intervals without motion, as if exhausted by their violence, the critical moment arrives: the skin splits in the back, in consequence of the still more violent swelling of the second or third segment: the opening thus made is speedily increased by a succession of swellings and contractions of the remaining segments: even the head itself often divides into three triangular pieces, and the inclosed larva by degrees withdraws itself wholly from its old skin. All larvæ, however, do not force their way through this skin in precisely the same place. Thus, those of the hawthorn butterfly (Pieris Cratægi), according to Bonnet[477] make their way out by forcing off what may be called their skull, or the horny part of their head, without splitting the skin, which remains entire; others have been observed to make their way out at the side and the belly. Reaumur noticed the larva of Zygæna Filipendulæ, previously to its last moult, actually biting off and detaching several portions of its old skin; and before this, drops of a fluid resembling water were seen to exude from it[478].

The skin when cast is often so entire, that it might be mistaken for the larva itself; comprising not only the covering of the main trunk with the hairs which clothed it, but of the very skull, eyes, antennæ, palpi, jaws, and legs; which, if examined from within, are now found to be hollow, and to have incased, like so many sheaths, similar parts in the new skin. That the feet of the newly-coated larva were actually sheathed, as fingers in a glove, in the same parts of the exuviæ, may be proved by a very simple experiment: if a leg of one just ready to cast its skin be cut off, the same limb will be found mutilated when that change has ensued. The anal horns, also, of the larvæ of the hawk-moth (Sphinx L.) and other similar protuberances, are incased in each other in like manner; but hairs are laid flat between the two skins, and contribute considerably towards their more easy separation. Thus, if you saved the skins cast by the larva of Callimorpha Caja, for instance, you would appear to have ten different specimens of caterpillars, furnished with every external necessary part, and differing only in size, and the colour perhaps of the hairs, and all representing the same individual.

But further changes than this take place. Swammerdam says, speaking of the moult of the grub of Oryctes nasicornis, a beetle common in Holland, but not satisfactorily ascertained to inhabit Britain, "Nothing in all nature is in my opinion a more wonderful sight than the change of skin in these and other the like worms. This matter, therefore, deserves the greatest consideration, and is worthy to be called a specimen of nature's miracles; for it is not the external skin only that these worms cast, like serpents, but the throat and a part of the stomach, and even the inward surface of the great gut, change their skin at the same time. But this is not the whole of these wonders; for at the same time some hundreds of pulmonary pipes within the body of the worm cast also each its delicate and tender skin. These several skins are afterwards collected into eighteen thicker, and, as it were, compounded ropes, nine on each side of the body, which, when the skin is cast, slip gently and by degrees from within the body through the eighteen apertures or orifices of the pulmonary tubes before described, having their tops or ends directed upwards towards the head. Two other branches of the pulmonary pipes that are smaller, and have no points of respiration, cast a skin likewise." ... "If any one separates the cast little ropes or congeries of the pulmonary pipes with a fine needle, he will very distinctly see the branches and ramifications of these several pipes, and also their annular composition[479]."--Bonnet makes a similar observation with regard to caterpillars; but he appears to have observed it more particularly, at least the change of the intestines, previously to the metamorphosis of the insect, when he says with the excrements it casts the inner skin of the stomach and viscera[480]. Both these great men appear to have recorded the result of their own actual observations with regard to the proceedings of two very different kinds of insects; the one the grub of a beetle, and the other the caterpillars of Lepidoptera. The account of the former is given quite in detail, as that of a person who is describing what he has actually seen: yet by a later and very able physiologist, Dr. Herold, it is affirmed that the inner skin of the intestinal canal is never cast, that canal constantly retaining its two skins. He further affirms, that they are only the large trunks of the Tracheæ that cast their skins, none being detached from their smaller ramifications[481]. When men so eminent for their anatomical skill and nicety, and for their depth and acumen, disagree, the question must be regarded as undecided till further observations throw sufficient weight into one scale or the other.

The larva which has undergone this painful process is at first extremely weak: all its parts are soft and tender; even the corneous ones, as the head and the legs, are then scarcely more than membranous, and are all bathed with a fluid, which, before the moult, intervenes between the two skins, and facilitates their separation[482]: and it is only after some hours, or in some cases even days, during which it lies without motion, that this humidity evaporates, all its parts become consolidated, and it recovers its strength sufficiently to betake itself to its wonted food. Its colour, too, is usually at first much paler than before, and its markings indistinct, until their tints have been enlivened by exposure to the air, when they become more fresh, vivid, and beautiful to appearance than ever. When a few meals have invigorated its languid powers, the renovated animal makes up for its long abstinence by eating with double voracity. . A similar preparatory fast, and succeeding state of debility, accompany every change of the larva's skin. Each time except the last, the old skin is succeeded by a new one, with few exceptions, similar to the one it has discarded. Previously to the final change, which discloses the pupa, it quits the plant or tree on which it had lived, and appears to be quite unsettled, wandering about and crossing the paths and roads, as if in quest of some new dwelling. It now abstains from food for a longer time than before a common moult, empties itself copiously, and as I have just said, if Swammerdam and Bonnet are to be depended upon, casts the skin that lines the stomach and intestines, as well as that of the Tracheæ.

I have observed above, that all larvæ, with few exceptions, change their skins in the manner that I have described. These exceptions are principally found in the order Diptera, of which those of the Linnean genera Musca, Œstrus, and probably all that, like the maggot of the common flesh-fly, have membranous contractile heads, never change their skin at all, not even preparatory to their becoming pupæ. The skin of the pupa, though often differing greatly in shape from that of the larva, is the same which has covered this last from its birth, only modified in figure by the internal changes that have taken place, and to which its membranous texture readily accommodates itself. The larvæ of the Dipterous genera Tipula, Culex, and those which have corneous heads, like other larvæ change their skins several times previously to becoming pupæ[483]. The grubs, also, of bees, wasps, ants? and probably many other Hymenoptera, do not change their skin till they assume the pupa, nor the larva of the female Coccus[484].

If you feel disposed to investigate the reasons of that law of the Creator which has ordained that the skins of the higher animals shall be daily, and imperceptibly, and as it were piece by piece renewed, while those of insects are cast periodically and simultaneously,--the proximate cause must be sought for in the nature of the two kinds of skin, the one being more pliable and admitting a greater degree of tension than the other, and being so constructed as to scale off more readily. If, ascending higher, you wish to know why the skins of insects are so differently circumstanced from our own, the most apparent reason is, to accommodate the skin to the very rapid growth of these animals, which a gradual and slower change would have impeded too much, or the skin have suffered constant dilapidation and injury; therefore their Beneficent Creator has furnished them with one which will stretch to a certain point, and during a certain period, and then yield to the efforts of the inclosed animal, and be thrown aside as a garment that no longer fits the wearer.

viii. And this leads me to a subject to which I am desirous now to bespeak your attention,--the Growth, I mean, and size of Insects in this state. As to size, larvæ differ as much as insects in their perfect state: these last, however, never grow after their exclusion from the pupa, while larvæ increase in bulk in a proportion, and often with a rapidity, almost without a parallel in the other tribes of animals. Thus Lyonnet found, that the caterpillar of the great goat-moth (Cossus ligniperda F.) after having attained its full growth is at least 72,000 times heavier than when it was first excluded from the egg[485]; and of course had increased in size in the same proportion. Connected with the size of larvæ, is the mode in which their accretion takes place. This, with respect to the more solid parts, as the head, legs, &c., is not, as in other animals, by gradual and imperceptible degrees, but suddenly and at stated intervals. Between the assumption of a new skin and the deposition of an old one, no increase of size takes place in these parts, while the rest of the body grows and extends itself, till, becoming too big for these solid parts, nature restores the equilibrium between them by a fresh moult[486], in which the augmentation of bulk, especially in these parts, is so great, that we can scarcely credit the possibility of its being cased in so small an envelope. Malpighi declares, that the head of a silk-worm that has recently cast its skin is four times larger than before the change[487]. It is very probable, also, that when the outer skin becomes rigid, it confines the body of the larva within a smaller compass than it would expand to if unconfined, so that, when this compression is removed, the soft and elastic new integument immediately swells out, and the animal appears all at once much larger than it was before the moult. In fact, the proximate cause of the rupture and rejection of the old skin is the expansion of the included body, which at length becomes so distended as to split its envelope, aided, indeed, as before described, by the contortions of the creature itself.

The larvæ most notorious for the rapidity of their growth are those of Musca carnaria and other flesh-flies: some of which Redi found to become from 140 to more than 200 times heavier in twenty-four hours[488]: an increase of weight and size in so short a time truly prodigious, but essential for the end of their creation--the rapid removal of dead and putrescent animal matter. As the skins of these larvæ are never changed, we may conclude, if the cause of the change of skin in other larvæ above surmised be accurate, that their skins are more contractile and capable of a greater degree of tension than those of larvæ that are subject to moulting. And two peculiarities observable in them confirm this idea: in the first place, their head is not hard and corneous, as that of the others, but capable of being shortened or lengthened; and in the next, their breathing-pores are not in the sides, but at the extremities of the body, while in the moulting larvæ there are two in almost every segment, which must form so many callous points that impede the stretching of the skin to the utmost. The hairs, spines, and tubercles, that are so often found on caterpillars, must also form so many points of resistance that prevent that full extension of the integument which it might otherwise admit.

There is not always that proportion between the size of larvæ and of the insects that proceed from them that might have been supposed, some small larvæ often producing perfect insects larger than some of those proceeding from such as are of greater size.

ix. As insects often live longest in the state we are treating of, I shall say something next upon the age of larvæ, or the period intervening between their exclusion from the egg and their becoming pupæ. This is exceedingly various, but in every case nicely adapted to their several functions and modes of life. The grubs of the flesh-fly have attained their full growth, and are ready to become pupæ, in six or seven days; the caterpillar of Argynnis Paphia, a butterfly, in fourteen days; the larvæ of bees in twenty days; while those of the great goat-moth (Cossus ligniperda) and of the cockchafer (Melolontha vulgaris) live three years, or at least survive three winters, before the same change. That of another lamellicorn beetle (Oryctes nasicornis F.) is said to be extended to four or five; that of the wire-worm (Elater segetum) to five. That of the stag-beetle (Lucanus Cervus) is affirmed by Rösel to be extended to six years; but the most remarkable instance of insect longevity is recorded by Mr. Marsham in the Linnean Transactions[489]. A specimen of Buprestis splendida, a beautiful beetle never before found in this country, made its way out of a deal desk in an office in London in the beginning of the year 1810, which had been fixed there in the year 1788 or 1789; so that according to every appearance it had existed in this desk more than twenty years. Ample allowance being made for its life as a pupa, we may conclude that it had existed as a larva at least half the above period. The grubs of the species of the genus Cynips L. attain their full size in a short time; but they afterwards remain five or six months in the gall before they become pupæ[490].

With few exceptions it may be laid down, that those larvæ which live on dead animals, in fungi, in dung, and in similar substances, are of the shortest duration in this state; and that those which live under the earth, on the roots of grass, &c. and in wood, the longest: the former becoming pupæ in a few days or weeks, the latter requiring several months, or even years, to bring them to maturity. The larvæ which live on the leaves of plants seem to attain a middle term between the one and the other,--seldom shorter than a few weeks, and rarely longer than seven or eight months. Aquatic larvæ appear to be subject to no general rule: some, as the larvæ of Gnats, becoming pupæ in two or three weeks; and others, as those of the Ephemeræ, which are thus compensated for their short life as flies, in as many years[491]. The cause of all these differences is obviously dependent on the nature of the food, and the purposes in the economy of creation to which the larvæ are destined.

x. The last part of the history of larvæ relates to their Preparations for assuming the pupa state. When they have acquired their full size, after having ceased to take food, by a copious evacuation they empty the intestinal canal, even rejecting the membrane that lines it and the stomach[492]; their colours either change totally, or fade; and they make themselves ready for entering upon a new stage of their existence. Some merely rest in a state of inactivity in the midst of the substances in which they feed, as if conscious of their inability to select any safer abode. Of this description are most Coleopterous, Hymenopterous, and Dipterous larvæ, that feed under ground, or in the interior of trees, fruits, and seeds.

But a still larger tribe, those which feed on leaves, animals, &c. act as if more sensible of the insecurity of this to them important epoch. They are about to exchange their state of vigour and activity for a long period of deathlike sleep. The vigilant caution which was wont to guard them from the attack of their enemies will be henceforward of no avail. Destitute of all the means of active defence, their only chance of safety during their often protracted night of torpor must arise from the privacy of their place of repose. About this, therefore, they exhibit the greatest anxiety. Many, after wandering about as if bewildered, retire to any small hole on the surface of the earth, covering themselves with dead leaves, moss, or the like, or to the chinks of trees, or niches in walls and other buildings, or similar hiding-places. Many penetrate to the depth of several inches under ground, and there form an appropriate cavern by pushing away the surrounding earth; to which they often give consistence by wetting it with a viscid fluid poured from the mouth. The larvæ of other insects undertake long and arduous journeys in search of appropriate places of shelter. Those of flesh-flies, now satiated with the mass of putridity in which they have wallowed, leave it, and conceal themselves in any adjoining heap of dust. The grubs of the gad-fly (Œstrus) creep some of them out of the backs of cattle, in tumours of which they have resided, and suffer themselves to fall to the earth; while others, which have fed in the stomach of horses, quit their hold, and by a still more extraordinary and perilous route are carried through the intestines the whole length of their numerous circumvolutions, and are discharged at the anus. And without enumerating other instances, various aquatic larvæ, as that of a common fly (Elophilus pendulus), &c. leave the water, now no longer their proper element, and betake themselves to the shore, there to undergo their metamorphosis.

Most of these, having reached their selected retreat, require no other precaution; but another large tribe of larvæ have recourse to further manœuvres for their defence before they assume the pupa. Those of the aphidivorous flies (Syrphus F. &c.), of the various lady-birds (Coccinella L.), and tortoise-beetles (Cassida L.), &c. fix themselves by the anus with a gummy substance to the leaves or twigs under which they propose to conceal themselves during their existence in that state. Others previously suspend themselves by a silken thread fixed to the tail, or passing round the body; by which also, when become pupæ, they are afterwards pendent in a similar position; and lastly, a very great number of larvæ wholly inclose themselves in cases or cocoons, composed of silk and various other materials, by which during their state of repose they are protected both from their enemies and the action of the atmosphere. As these two last-mentioned processes are extremely curious and interesting, I shall not fear tiring you by entering into some further detail respecting them: explaining first the mode by which larvæ suspend themselves, both before and after they are become pupæ, by silken threads; and next, the various cases or cocoons in which others inclose themselves, and their manner of operating in the formation of them.

1. The larvæ which suspend themselves and their pupæ, with the exception of the tribe of Alucitæ, and some Geometræ of the family of G. pendularia, punctaria, &c. are almost all butterflies[493]. No others follow this mode. They may be divided into two great classes--those which suspend themselves perpendicularly by the tail, and those which suspend themselves horizontally by means of a thread girthed round their middle. In both cases it should be observed, that the suspension of the pupa is the object in view; but as the process is the work of the larva, this seems the proper place for explaining it. To begin with the first case.

You are aware that all lepidopterous larvæ have the faculty of spinning silk threads from their mouths, and it will readily occur to you that it is by means of these threads that they suspend themselves. But how? How is a caterpillar to hang itself by the tail to threads spun from the mouth? Even suppose this difficulty overcome, others still greater remain. Suppose the caterpillar to be suspended by its tail,--this is but a preparatory operation,--what is required is, that the pupa shall hang in the same position: now when you take into consideration that it is incased within the skin of the larva, and without feet or other external organs; that it has to extricate itself from this skin; to hang itself in its place, and to detach the skin from the threads which hold it--this will appear no trifling task. Indeed at first view it seems impossible. Country-fellows for a prize sometimes amuse the assembled inhabitants of a village by running races in sacks: take one of the most active and adroit of these, bind him hand and foot, suspend him by the bottom of his sack with his head downwards, to the branch of a lofty tree; make an opening in one side of the sack, and set him to extricate himself from it, to detach it from its hold, and suspend himself by his feet in its place. Though endowed with the suppleness of an Indian juggler, and promised his sack full of gold for a reward, you would set him an absolute impossibility: yet this is what our caterpillars, instructed by a beneficent Creator, easily perform. Their manœuvres I shall now endeavour to explain.

When the caterpillar has selected the under-side of the leaf or other object to which it purposes suspending itself, its first process is to spin upon it a little hillock of silk consisting of numerous loosely interwoven threads; it then bends its body so as to insinuate the anal pair of prolegs amongst these threads, in which, by a slight exertion, the little crochets which surround them[494] become so strongly entangled as to support its weight with ease. It now suffers the anterior part of the body to fall down, and it hangs perpendicularly from its silken support with its head downwards. In this position it remains often for twenty-four hours, at intervals alternately contracting and dilating itself. At length the skin is seen to split on the back near the head, and a portion of the pupa appears, which by repeated swellings acts like a wedge, and rapidly extends the slit towards the tail. By the continuance of these alternate contractions and dilatations of the conical pupa, the skin of the caterpillar is at last collected in folds near the tail, like a stocking which we roll upon the ancle before withdrawing it from the foot. But now comes the important operation. The pupa, being much shorter than the caterpillar, is as yet at some distance from the silken hillock on which it is to be fastened; it is supported merely by the unsplit terminal portion of the latter's skin. How shall it disengage itself from this remnant of its case, and be suspended in the air while it climbs up to take its place? Without arms or legs to support itself, the anxious spectator expects to see it fall to the earth. His fears, however, are vain; the supple segments of the pupa's abdomen serve in the place of arms. Between two of these, as with a pair of pincers, it seizes on a portion of the skin; and bending its body once more, entirely extricates its tail from it. It is now wholly out of the skin, against one side of which it is supported, but yet at some distance from the leaf. The next step it must take is to climb up to the required height. For this purpose it repeats the same ingenious manœuvre, making its cast-off skin serve as a sort of ladder, it successively with different segments seizes a higher and a higher portion, until in the end it reaches the summit, where with its tail it feels for the silken threads that are to support it. But how can the tail be fastened to them? you ask. This difficulty has been provided against by Creative Wisdom. The tail of the pupa is furnished with numerous little hooks pointing in different directions[495], as well adapted to the end in view as the crochets of the larva's prolegs, and some of these hooks are sure to fasten themselves upon the silk the moment the tail is thrust amongst it. Our pupa has now nearly completed its labours; it has withdrawn its tail from the slough, climbed up it, and suspended itself to the silken hillock--manœuvres so delicate and perilous, that we cannot but admire that an insect which executes them but once in its life, should execute them so well: nor could it, as Reaumur has well and piously observed, had it not been instructed by a GREAT MASTER. One more exertion remains: it seems to have as great an antipathy to its cast-off skin, as one of us should, when newly clothed after a long imprisonment, to the filthy prison garments we had put off. It will not suffer this memento of its former state to remain near it, and is no sooner suspended in security than it endeavours to make it fall. For this end--it seizes, as it were with its tail, the threads to which the skin is fastened, and then very rapidly whirls itself round, often not fewer than twenty times. By this manœuvre it generally succeeds in breaking them, and the skin falls down. Sometimes, however, the first attempt fails: in that case, after a moment's rest, it makes a second, twirling itself in an opposite direction; and this is rarely unsuccessful. Yet now and then it is forced to repeat its whirling, not less than four or five times: and Reaumur has seen instances where the feet of the skin were so firmly hooked, that after many fruitless efforts the pupa, as if in despair, gave up the task and suffered it to remain[496]. After these exertions, it hangs the remainder of its existence in this state until the butterfly is disclosed.

We are now to consider the second mode of suspension, in which larvæ by means of a silken girth round their middle, fix themselves horizontally under leaves, &c. These follow the same process with that of those last described, in spinning a small hillock of silk to which they fasten their hind legs; and if the operation concerned the larva state alone, this would be sufficient, as by means of this support, and of their prolegs, they could easily retain themselves in a horizontal position. But these larvæ act as if they foresaw the assumption of a state in which they will be deprived of legs. It is the suspension of the forthcoming pupa that is the object in view; and though this can be hung by the tail in the same way with those of the first class, yet it is plain that it cannot be retained in a horizontal position, which for some unknown reason is essential to it, without some support to its anterior extremity. It is necessary for the larva, therefore, not only to fix its posterior legs amongst a collection of silken fibres, but to spin a girth of the same material round its body. This girth, though apparently of a single thread, will be found on examination to be composed of several, often as many as fifty or sixty; and is fastened on each side of the body of the larva about the middle, to the surface under which it is placed. Three different modes of fixing these girths are adopted by the caterpillars of different butterflies. Some, as those of the common cabbage-butterfly (Pieris Brassicæ), which have remarkably pliable bodies, bend them almost double on one side, then fix the thread and carry it over to the other in the same position, repeating this operation as often as is necessary. Others, as that of Lycæna Argus and many more of the Papiliones Rurales and Urbicolæ L., which have a short and more rigid body, after having bent the head on one side so as to fix one end of the thread, bring themselves into a straight position, and, by a manœuvre not easily described, contrive to introduce the head under the thread, which they then bend themselves to fasten on the other side, pushing it to its proper situation by the successive tension and contraction of their segments. But the most curious mode, though indeed that which seems most natural, is adopted by the caterpillar of the beautiful swallow-tail butterfly (Papilio Machaon) and others of the same family. This first forms the loop which is to serve for its girth, and then creeps under it. But the difficulty it has to surmount is, to keep itself from being entangled in the fifty or sixty fine distinct threads of which the girth is composed, and to preserve them all extended so as to be able to introduce its body beneath them. For this purpose it makes use of the two first pair of its fore-legs, employing them as a woman does her hands in winding a skein of cotton, to collect and keep all the threads of its card unentangled and properly stretched; and it is often with great difficulty, towards the end of the process, that it prevents them from slipping off. When a sufficient number of threads is completed, the animal bends its head between its legs, and insinuates it under the collected loop, which by its annular contraction it easily pushes to the middle of the body.

In about thirty hours after the larvæ which girth themselves have finished their operations, the skin splits, and the pupa disengages itself from it by those contractions and dilatations of its segments which have been before described, pushing the exuviæ in folds to the tail, by different motions of which it generally succeeds in detaching them. One would have thought there would be considerable difficulty in slipping the skin past the girth; but this, according to Reaumur, seems to be easily effected[497].

If you are desirous of witnessing for yourself the manœuvres by which these curious modes of suspension are effected, you may be readily gratified. It is only necessary to collect and feed until their metamorphosis the black spinous caterpillars of the common peacock-butterfly (Vanessa Io), which in most places may be found upon nettles, or those of the Pieris Brassicæ, which swarm in cabbages or brocoli in every garden. The former will exhibit to you a specimen of vertical, the latter of horizontal suspension. It should be observed, however, that to hit the precise moment when these processes are going on, it is necessary to feed a considerable number of the larvæ of each kind; some one of which, if you watch them narrowly when they have attained their full growth, you will scarcely fail to surprise in the act.

I must observe here, that although the vertical and horizontal are the two principal positions in which caterpillars suspend themselves, yet that others are inclined at various angles; and some are attached with less art, appearing only to be fastened by some part of their abdomen to the body upon which they are fixed[498].

2. The larvæ whose procedures I am in the next place to describe, are those which, previously to assuming the pupa state, inclose themselves in cases or cocoons of different materials. For the sake of method, I shall divide these into two great classes: First, those which form their cocoons entirely or principally of silk; and secondly, those which form them chiefly of other substances.

To begin with the first. The larvæ which inclose themselves in silken cocoons are chiefly of the Lepidopterous tribes of Bombycidæ and Noctuidæ; but a few Geometræ (G. papilioniaria, lactearia, &c.); most of the Hymenoptera; some Coleoptera, as certain of the weevil tribe (Hypera Arator, Rumicis Germ.), and those brilliant beetles frequenting aquatic plants constituting the genus Donacia F.; the Neuropterous genera Hemerobius and Myrmeleon; Mycetophila and a few others in the Diptera; and Pulex in the Aphaniptera fabricate coverings of the same material. In all, with the exception of Myrmeleon and Hemerobius (and perhaps Hypera Rumicis, &c.?) which have their spinning apparatus at the extremity of the abdomen, the silken thread employed in forming these coverings proceeds from the middle part of the under-lip, as before explained; and is in fact composed of two threads gummed together as they issue from the two adjoining orifices of the spinner.

Of the larvæ which inclose themselves in silk, the most familiarly known is the silk-worm: the cocoon of this consists exteriorly of a thin, transparent, gauze-like coating, through the interstices of which can be seen an inner, smaller, oval ball of a more close and compact texture. The whole is in fact composed of one single thread, but arranged in two distinct modes. To form the exterior envelope, which is merely the scaffolding by means of which the inner and more solid covering is constructed, the caterpillar, after fixing upon a space between two leaves or twigs or angles suitable for its purpose, begins by glueing one end of its thread to one of the adjoining surfaces. This thread it next conducts to another part and then fastens, repeating this process and interlacing it in various directions, until it has surrounded itself with a slight and loosely spun netting. In the centre of this, when contracted into a space sufficiently small, it lays the foundation of the interior cocoon. Fixing itself by its prolegs to some of the surrounding threads, it bends its body, and by successive motions of its head from side to side spins a layer of silk on the side opposite to it: when this is of the requisite thickness, the larva shifts its position, and repeats the same process in another quarter, covering each layer in turn with a new one until the interior cavity is reduced to the size desired. Thus, the silken thread which forms this new cocoon is not, as might have been supposed, wound circularly as we wind the thread of a ball of cotton; but backwards and forwards in a series of zigzags, so as to compose a number of distinct layers. Malpighi could distinguish six of these layers[499], and Reaumur suspects there is often a greater number[500]. The former found the length of the thread of silk composing them when wound off, without including the exterior case, to be not less than 930 feet[501]; but others have computed it at more than a thousand[502]: consequently the threads of five cocoons united would be a mile in length. Estimating by the weight,--the thread of a pound of cocoons, each of which weighs about two grains and a half, would extend more than 600 miles[503], and such is its tenuity, that the threads of five or six cocoons require to be joined to form one of the thickness requisite in the silk manufacture. It is the continuous thread of the inner cocoon which is most valuable; the outer loose coating from its irregularity cannot be wound off, and is known in commerce by the name of floss silk.

Manœuvres in their general principle similar to those of the silk-worm are followed by most of those larvæ which inclose themselves in silken cocoons. Many species, however, adopt variations in the mode of procedure all of which it would be tedious to particularize, but some of them are worth mentioning. The larvæ of Tortrix prasinana, and other species of moths which form cocoons resembling a reversed boat, arrange their threads in layers, so as to construct two parallel walls gradually inclining towards the top and ends, where they finally force them to approach each other by means of an apparatus of silken cables[504]. And the larva of Saturnia Pavonia, though it forms the base of its flask-shaped cocoon by spinning like the silk-worm a number of interwoven zigzags, places the threads which compose the interior funnel-like opening of the apex nearly straight, parallel to each other, and converging towards the same point in the centre[505].

These last, as well as almost all larvæ, constantly remain in the inside of the cocoon during its construction. But De Geer has given us the history of a minute caterpillar of a species of moth (Tinea L.) which feeds on the under side of the leaves of the Rhamnus Frangula, or Black Alder, that actually weaves half of its cocoon on the outside. This cocoon, which is very small, is beautifully fluted, consisting of several longitudinal cords, with the intervals filled by fine net-work, and shaped like a reversed boat[506]. The animal begins by laying the foundations of one of the ends of her cocoon, she adds new threads to this small beginning, and so proceeds. As the work advances she retreats backwards, and her body is situated nearly in the same line with the cocoon she has begun, and quite out of it; she only touches with her head and legs its anterior margin. When half the cocoon, or rather of its exterior layer, is finished, she suspends her operations for some moments. She then for the first time introduces her head into this demi-cocoon, and turns herself in it by doubling her supple body, and passing one part over the other, so that at last she manages to bring her tail into the pointed end of the cocoon, the head and the anterior half of her body remaining without. Thus situated, she commences her operations afresh. At a distance from the margin of the demi-cocoon, equal to its length, she begins to spin the pointed end of the other moiety, the length of her body serving her as a measure that enables her to begin at the proper distance from it. This new portion she spins in the same manner as the other; but as she is prevented by the demi-cocoon in which the posterior part of her body is lodged from retreating backwards, she contracts her body more, which answers the same purpose. When the new work is so advanced that she can no longer contract her body, she bends the anterior part of it considerably, and reverses her head. When the distance between the margin of the two halves of the cocoon is very small, so as no longer to admit the head between them, in order to unite them she is obliged to have recourse to another manœuvre. Withdrawing her head, she extends silken longitudinal threads between the two margins, and thus unites them. This part is more clumsy, and not so regular as the rest of the cocoon, so that the point of union is always discoverable. These caterpillars do not always divide the cocoon into two equal portions, for often they will finish three quarters of the cocoon before they enter it, and begin at the other end[507].

The general rule is,--that each larva spins for itself a separate cocoon; but amongst those of Arctia chrysorhea and others which live in society, two or three sometimes begin their operations so close together that they are under the necessity of forming one common cocoon, which serves for a covering to the whole number. The same thing happens to silk-worms, the double or treble cocoons of which are called Dupions by the breeders. The larvæ of some Ichneumons, besides forming each its separate cocoon, spin a joint cottony covering for the whole[508], which is effected thus:--After they leave the caterpillar they have devoured, they fix themselves side by side at a little distance from it, and begin to spin each a cocoon; and in order to defend its end and side that is not covered by others, they spin further an envelope of loose silk, and thus this exterior covering is formed.

The size, figure, colour, substance, and texture of silken cocoons are extremely various. Their size indeed is usually proportioned to that of the included larva or pupa; yet it is by no means always so. Some large caterpillars spin cocoons so small, that the observer can hardly conceive how they can be contained in so narrow a compass: Eriogaster Catax is a moth of this description[509]. And others smaller in size lodge themselves in apartments apparently much more spacious than necessary. The transparent hammock-like cocoons of Hepialus Humuli and Arctia villica, two other moths, would contain several of their pupæ. I possess one in which the pupa is suspended in the centre, that is ten times its size, and not very short in dimensions of that of Attacus Paphia, a giant silk-moth. The largest cocoon I ever read or heard of, is that thus described by Mr. Hobhouse in his Travels: "Depending," says he, "from the boughs of the pines, near the Attic mountain Parnes, and stretching across from tree to tree so as to obstruct our passage, were the pods, thrice as big as a turkey's egg! and the thick webs of a chrysalis, whose moth must be far larger than any of those in our country."[510] If this statement is correct, and I am not aware that there is any reason for doubting it, the cocoon must be vastly larger than the pupa, or the moth it produced would far exceed in size any yet known. Perhaps, however, as this gentleman is probably no entomologist, what he took for a cocoon might be a nidus, in which many larvæ were associated, of the nature of those formerly described[511].

With regard to figure, the majority are like those of the silk-worm, of a shape more or less oval or elliptic: some, however, vary from this. That of Lasiocampa Rubi is oblong. I have one from New Holland somewhat resembling an acorn, fixed to the twigs of some tree or shrub, of a very close silk, and covered by a circular operculum, which the animal pushes off when it assumes the imago; this is ovate or conico-ovate; others again are globose[512]; others are conical[513], as that of Gastropacha quercifolia; others almost fusiform[514] (Odenesis potatoria). Reaumur received one from Arabia which was nearly cylindrical[515]. Those of T. prasinana before noticed, and many other Tortrices, are shaped like a reversed boat[516]; that of Saturnia Pavonia and others of the same tribe, like a Florence flask with a wide and short neck. The cocoon of Lygæna Filipendulæ resembles a grain of barley. Another cocoon in my cabinet, of very slight network, is shaped something like an air-balloon. But the most remarkable one for its form and characters, is one that I received from the rich cabinet above quoted. This, which is of an unusually close texture, is suspended by a thread more than two inches long from the point of a leaf; it then swells into a perfect cone, at the base about four-fifths of an inch in diameter and half an inch in length, and covered with scattered setiform appendages: from the centre of the base projects a large hemispherical protuberance, which terminates in a long stalk, much thicker than the thread that suspends the cocoon. There is commonly no difference between the shape of cocoons spun by larvæ which are to give birth to different sexes of the same species. The silk-worm cocoons, however, which will produce male moths, have more silk at the ends, and consequently are more round than those which are to produce females: but the difference is not striking.

The most usual colour of silken cocoons is white, yellow, or brown, or the intermediate shades. The whites are very pure in the general envelope of some species of Ichneumonidæ, and yellows often very brilliant. But besides these more general colours, some cocoons are black[517], some few blue or green, and others red[518]. Sometimes the same cocoon is of two different colours. Those of certain parasites of the tribe of Ichneumones minuti L. the motions of one of which I noticed on a former occasion[519], are alternately banded with black or brown and white, or have only a pale or white belt in the middle, which gives them a singular appearance. In both cases the difference in colour depends upon the different tints with which the silky gum is imbued in the reservoirs: the first portion of it is white, and with this the larva first sketches the outline of its cocoon, and then thickens the layers of silk considerably in those parts where the white bands appear: when these are finished, its stock of white silk is exhausted, and the remainder of the interior of the cocoon is composed of brown silk[520]. The circular operculum above mentioned as covering an acorn-shaped cocoon, is paler than the latter, and also ornamented by a zone within the margin of deep brown. The pale cocoon also of Attacus Paphia is veined with silk of a deep red.

I have very little to say on the substance of the silk of cocoons. Though that of the silk-worm is composed of such a slender thread, that of many others is still finer, scarcely yielding in tenuity to the spider's web. On the other hand, the silk of the cocoons of Saturnia Pavonia and of several foreign species is as thick as a hair.

With regard to the texture of their cocoons--in some, as in that of the silk-worm, the threads are so slightly glued to each other, as to separate with facility; but in that of the emperor-moth just mentioned they are intimately connected by a gummy matter, furnished, as Reaumur conjectures, from the anus[521], with which the whole interior of the cocoon is often plastered. Some, as that of the silk-worm, are composed of an exterior loose envelope, and an inner compact ball; others have no exterior covering, the whole cocoon being of an uniform and thick texture. The larva of Cossus Robiniæ Peck, in spinning its cocoon, makes the end next the opening to the air, by which the imago is to emerge, of a slighter texture than the rest of it[522]. The exterior case is sometimes, as in Laria pudibunda, very closely woven, so as to resemble a real cocoon[523]: its form is usually adapted to that of the inner one; but in some which fix them under flat surfaces (Laria fascelina, Callimorpha Caja,) it resembles a hammock[524]. Cocoons of a close texture have generally no orifice in any part; but that of Eriogaster lanestris is spun with openings, as if bored from without, the use of which, however, does not seem to have been ascertained[525].

Many silken cocoons are of so close a fabric, as, when finished, entirely to conceal the included insect; but a very considerable number are of a more open texture, composed of a much smaller quantity of silk, and that woven so loosely, that the larva or pupa may always be discovered through it. Of this description are the cocoons of Hypogymna dispar, Arctia Salicis, &c., which consist only of a few slight meshes. Those of some others resemble gauze or lace[526]. Of the first description is one in my cabinet before alluded to, shaped somewhat like an air-balloon; the meshes are large and perfectly square. The pupa hangs in the centre, fixed by some few slight threads which diverge from it to all parts of the cocoon--so that it looks as if it was suspended in the air, like Mahomet's coffin, without support. Of the second description is a black one with very fine and nearly circular meshes: the threads that form these are thick, and seem to be agglutinated. In our own country, the cocoons of some beetles, as of Hypera Arator, Galeruca Tanaceti, and of some little Tineæ, also resemble gauze. Many of the larvæ, however, which spin these cocoons, whose thinness is probably attributable to the smallness of their stock of silk, seem anxious for a more complete concealment; and therefore commonly either hide them between leaves tied together, in some with a certain regularity, in others without art[527]; or thicken their texture, and render it opaque, by the addition of grains of earth[528], or of other materials with which their bodies supply them. These are principally of two kinds. The larvæ of Lasiocampa Neustria, Arctia Salicis, &c. after spinning their cocoons, cast from their anus three or four masses of a soft and paste-like matter, which they apply with their head all round the inside of the cavity; and which, drying in a short time, becomes a powder that effectually renders it opake. This is not, as might be conjectured, an excrement, but a true secretion, evidently intended for this very purpose: and, according to Reaumur, a similar powder, but white, derived from the varicose intestines, is used by the caterpillars of Gastropacha quercifolia, &c.[529] The other material, which is still more frequently employed, and which is occasionally mixed with the former, is the hair which everyone has observed to cover so thickly the bodies of some caterpillars. This, after spinning a sufficient envelope, they tear, or in some instances cut off with their mandibles, and distribute all round them, pushing it with their head amongst the interstices of the silk, so as to make the whole of a regular thick texture. After this process, which leaves the body completely denuded, and often seems to give them great pain, they conclude by spinning another tissue of slight silk, in order to protect the forthcoming pupa from the surrounding prickly points. It should be observed, however, that though many hairy larvæ, as those of Noctua Aceris, Arctia Caja, and others, employ their hairs in the composition of their cocoons, the rule is not general, several never making any such use of them. Nor do all that do so employ them distribute them in the same manner as those above described, which rarely attempt to arrange them in any regular position. Reaumur has noticed a small hairy caterpillar that feeds on lichens, which is more methodical: this actually places its hairs upright, side by side, as regularly as the pales in a palisade, in an oval ring around its body, connecting them by a slight tissue of silk, which forces them to bend into a sort of roof at the top; and under this curiously-formed cocoon assumes its state of pupa[530]. Some larvæ make so much hair and so little silk enter into the composition of their cocoons, that on the first inspection they would be pronounced wholly composed of it[531]; others, thickening the interior of their cocoon with hair, line the whole with a viscid matter like varnish[532].

The larvæ of some saw-flies (Tenthredo L.) are remarkable for inclosing themselves in a double cocoon, in which the inner is not, as in the silk-worm &c., connected with the outer, but perfectly distinct from it. Some species, as T. Rosæ (Cryptus Jur.), which have but a small stock of silk, compose the outer cocoon of thick silken cords crossing at right angles, and forming an oval net; which at the same time that it protects them effectually from the ants, which are always ready to attack them, demands much less silk than a covering of a closer texture. But the tender nymph itself requires to be inclosed in a case of a softer and more delicate substance; and accordingly the inner cocoon is composed of fine silk, woven so closely that the threads are scarcely perceptible under a microscope[533]. Reaumur mentions a hymenopterous larva belonging to Latreille's Fossores (Sphex L.) which thickened its cocoon with the legs, wings, and other relics of the flies which it had devoured[534]: trophies--like the drinking-cups of some savages, made of the skulls of their enemies, or the skull pyramid near Ispahan--of its powers of devastation.

It is a general rule, that those larvæ which spin cocoons, never in ordinary circumstances become pupæ without having thus inclosed themselves. An exception, however, is met with in the larva of a species of ant noticed by De Geer (Formica fusca L.), some of the individuals of which inclose themselves in cocoons; while others neglect this precaution, and undergo their metamorphosis uncovered[535]. Rösel also made nearly the same observation on the larva of the flea[536].

I must say something with regard to the situation, often very remote from their place of feeding, in which larvæ fabricate their cocoons. A very considerable number, probably the majority, form them either partially (Arctia lubricipeda) or wholly under ground; others beneath dead leaves, moss, or in the chinks of the trees; others within the wood in substances on which they have fed; the larva of Cossus leaves in these a communication with the open air by which the imago emerges; and a large number attach them to the leaves and branches of trees and plants; the cocoon of Donacia fasciata(?) is fastened by one side to the roots or surculi of Typha latifolia. There is usually nothing very remarkable in the mode of fixing them, the exterior threads being merely gummed irregularly to different portions of the objects which support them. But some effect this with greater art. I have one from New Holland, very long, which is suspended from a twig by a long riband, as it were, which entirely girths the twig. The larva of the magnificent silk-moth, Attacus Paphia, actually forms a solid silken stalk to its cocoon, an inch and half in length and a line in diameter, fastened by the other extremity to a twig, which it closely surrounds as if with a ring, at first sight resembling a fruit of a very singular appearance[537]. I have specimens of this cocoon with both stalk and ring. A bell-shaped cocoon fastened by a foot-stalk, but of softer consistence, to a blade of grass, found by Mr. Sheppard, I can also show you; and my friend Mr. Wilkin had a similar one out of the late Mr. Hudson's collection. Most larvæ spin their cocoons in solitude: some of those, however, which live in society do it close together under their common tent.

There are other cocoons that should be noticed here, such as those formed by the larva of Zygæna Filipendulæ, and some Bombyces, saw-flies (Tenthredo L.), and beetles (Curculio, Donacia F.), &c. These are formed of a substance which seems more analogous to gum than silk, yet furnished from the silk reservoirs, and usually present the appearance externally of parchment or membrane. That of the insect first mentioned is coated, however, with a slight interior silken lining; as indeed are almost all cocoons, of whatever substance.

* * * * *

The second class, into which I have divided larvæ that inclose themselves in cocoons, includes those which form their coverings not solely or principally of silk, but in which other materials are mixed more or less. The cocoons of some of these larvæ are merely composed of a few leaves slightly tied together, either irregularly, or arranged, particularly when they are of a linear figure, with considerable symmetry. The grubs of many beetles, as of the rose-beetle, Cetonia aurata, &c., prepare themselves a cocoon, composed of earth, pieces of rotten wood, and any substances within their reach: which they fasten together with a glutinous secretion. The same material is employed by others in forming a cocoon wholly of earth; which is sometimes, as that of the stag-beetle, Lucanus Cervus, exceedingly hard; at others, as that of some moths, Noctua ambigua, &c, so slight as to fall to pieces as soon as touched[538]. Other cocoons are formed of grains of earth. Reaumur has given a very interesting account of the procedures of a larva in repairing one of these cocoons, from which he had broken off the top when just completed. Without quitting the interior of the walls that remained, it put out its head from the breach, and for more than an hour employed itself in selecting one by one grains of earth, which it conveyed with its mandibles and deposited within its case: it next spun all round the opening threads of silk, to which it attached grains of earth taken from the previously-stored heap, uniting them compactly by means of other silken threads. After employing three hours in this laborious process, the industrious little mason had reduced the diameter of the breach to a few lines. Reaumur was very curious to know how it would fill up this orifice, which would no longer admit the protrusion of its head outside the walls, as in its previous operations. He concluded, that while the rest of the cocoon was exteriorly formed of earth, this opening would be merely closed with silk. He was mistaken, however: the artist knew how to vary its manœuvres, and make its vault of one uniform texture. It spun across the opening a little net of silk, between the meshes of which it thrust grains of earth so dexterously that they projected as far as the outer surface, retained there probably by silken lines previously attached and fastened within. It then finished its habitation by fortifying the inside of the orifice with another layer of earth[539]. The ant-lion (Myrmeleon) spins a globular cocoon with its anus, which it covers with grains of sand[540]. One that I took in the forest of Fontainebleau, in the quarry that produces the crystallized sandstone called the Fontainebleau fossil, was covered with large and shining grains. Instead of the grains of earth or sand employed by these larvæ, those of another tribe substitute grains of stone detached from the softer walls, upon whose lichens they previously feed, which they unite into solid oval cocoons[541]. Those of a fourth form their cocoons of patches of short moss arranged with the roots downwards, and forming a vault, as it were, of verdant turf, admirably adapted for concealment[542]. The larvæ of some moths form their cocoons of irregular pieces of bark tied together with silk, and resembling when completed a knotty protuberance of the twig on which they are fixed. That of Pyralis tuberculana constructs a pannier-shaped one of the parenchyma of the leaves of plants[543].

All these cocoons, however, must yield in point of singularity of construction, materials, and ingenuity, to one formed by a small caterpillar, described by the illustrious naturalist lately quoted, which feeds upon the oak. This cocoon is wholly composed of small rectangular strap-shaped pieces of the fine upper skin, or epidermis of the twig upon which it rests, regularly fastened to each other in a longitudinal direction with very slender silken cords. But the mode of its construction is even more remarkable than the substance of which it is fabricated. The caterpillar's first process is to form its slips of bark into two flat triangular wing-like pieces, projecting opposite to each other from each side of the twig, somewhat like the feathers of an arrow. It does not, perhaps, require any great degree of intelligence in a larva to give its cocoon the usual oval form, when it begins to arrange its materials in that shape from the very first, and round so good a mould as its own bent body; but we surely must admit that it is a task to which no stupid artist would be competent, to form first a multitude of strap-shaped laminæ into two triangular plates, and then to bend these plates into a case resembling the longitudinal section of a cone, with an elliptical and protuberant base,--the figure which the cocoon of this insect assumes. All the minutiæ of the manœuvres which it employs in this nice operation could not be comprehended without a more diffuse explanation than I have here room to give: suffice it to say, that the caterpillar fastens silken lines to each exterior opposite and longer side of the laminæ, and by applying all the weight of its body forces them to bend and approach each other, in which position it secures them by other shorter lines. It next repeats the same process with the upper and shorter sides of the plates; which when joined form the base of the cocoon. Both these tasks are accomplished in less than an hour, and the seams are so nicely joined as to be imperceptible. A fine inner tapestry of silk, covering all the asperities of the exterior walls, concludes its labours[544]. It is to be lamented that Reaumur was unacquainted with the moth that proceeds from the pupæ inclosed in these ingenious cocoons; which being small, and precisely of the same colour as the bark of the twig that supports them, are not to be discovered but by a very narrow inspection. It would seem, however, to be Noctua Strigula of Berkhausen, Pyralis strigulalis of Hubner[545]. The larva, he informs us, is found in May: its body is flatter than common, of a yellowish flesh-colour, clothed with tufts of red hair on each segment, and furnished with fourteen feet. Should this description enable you to detect it upon your oaks, a view of its ingenious procedures would amply repay you for the trouble of seeking for it. The larvæ of Cerura vinula, Stauropus Fagi, and several other moths, form their cocoons of grains of wood gnawed from the trees on which they feed. These grains they masticate, mixed with a glutinous fluid secreted from the mouth, into a paste, which forms a covering of an uniform smooth texture, and so hard as not readily to yield to a knife. Of a substance apparently nearly similar is composed the cocoon of a weevil related to Liparus Pini; which with its inhabitant was given me by the ingenious Mr. Bullock. A little moth, whose ravages have been before noticed[546], lines the interior of the grain of barley, of which it has devoured the contents, with silk; divides it into two apartments, into one of which it pushes the excrement it had voided, and in the other assumes the pupa[547].

These, and the other larvæ mentioned above, commonly form their cocoons of the substances I have indicated; but when by any cause they are prevented from access to them, they often substitute such other materials as are at hand. Reaumur fed a larva that formed its cocoon of minute fragments of paper, which with its mandibles it had cut from the piece that covered the glass vessel that contained it[548]: and the same circumstance happened to Bonnet.

Upon a former occasion I described to you the cases of various kinds formed and inhabited by the insects of the Trichoptera Order (Phryganea L.) commonly called case-worms[549]. As these serve for the pupa as well as the larva, they may be regarded as a kind of cocoon. I shall not repeat here what I then said; but having purchased from the collection of the late Mr. Francillon some that seem to belong to this or some cognate tribe, that are of a curious construction, I shall give you some account of two or three of them in this place. The first is not quite three inches long, of a sublanceolate shape, but rather widest towards one end. It consists of an internal tough and thick bag or cocoon, of a silk resembling fine wool of a dirty white colour, which is closely covered transversely by pieces of the stalk of a plant, about three-fourths of an inch in length, and crossing each other at an obtuse angle. The next is thicker and shorter: the internal bag is just covered with small fragments of wood like sawdust; over these are fastened irregularly, short stout pieces of a pithy stick or stalk, and the whole is clothed with a very close-woven ash-coloured web. It seems difficult to conceive how the inclosed animal could contrive to cover her habitation with this web without going wholly out of it. The third is the most curious and remarkable of all. It is nearly six inches long, and about four-fifths of an inch in diameter. It consists of a bag of thick cinereous silk web, to which are fastened, in a sextuple series, pieces of stick about an inch long, the end of one mostly resting upon the base of another: between each series a space of about three-tenths of an inch intervenes, but at the apex they all converge. This probably imitates the branch or stem of some tree or plant, in which the leaves are linear, and diverge but little from the stem. A label upon it states its country to be New Holland. I suspect the inhabitants of the two last cocoons to be terrestrial animals: the first is probably a true aquatic case-worm.

* * * * *

The same purpose for which the cocoons above described serve, is answered in the case of numerous Dipterous insects, by a humble and less artificial contrivance--the skin, namely, of the larva; which, as was before observed[550], is never cast, but, when the insect is about to enter into the pupa state, assumes a different form and colour; becomes of a thicker and more rigid texture; and defends the included pupa, which is separate from it, till its exclusion. In this case the mouth of the larva is constantly different from that of the perfect insect, or at least has not with it those relations as to number and kind of organs, which have been observed in the mouth of other larvæ compared with the insects that they produce. The animal, immediately after it is clothed with this skin, if it is opened, exhibits only a soft gelatinous pulp, in the surface of which the exterior organs of the adult insect cannot yet be detected. Nature requires more time for their elaboration, or at least for the appearance of their outline, and to consolidate them. This pulp first takes an oblong form (Boule allongée Reaum.), and afterwards that of the insect it is destined to give birth to[551]. The skin of the larva also serves for a cocoon to the pupæ of male Cocci[552]. The grub of the genus Anthrenus, so destructive to our cabinets of natural objects[553], when it assumes the pupa does not quit its skin, but only splits it open longitudinally on the back, and when it becomes an imago makes its exit through the orifice[554]. Some Lepidopterous larvæ even (Alucita pentadactyla, Callimorpha rosea, &c.) assume the pupa state within their last skin[555].

* * * * *

When a larva has finished its cocoon,--which with some species, that proceed so earnestly as though they had not a moment to lose, is the work of a few hours, of others about two or three days,--after a certain interval it casts its last skin, which is usually suffered to remain in the cocoon (but which one moth, Geometra lacertinaria, ejects through an opening purposely left in its bottom), and the pupa makes its appearance[556]. This interval is exceedingly various. Most larvæ assume the pupa state within a few days after they have formed their cocoons; but some not for several weeks, or even months. The caterpillar of Bombyx cæruleocephala, according to Rösel, lies three weeks in the cocoon before this change is effected; those of many Pupivora and Diplolepariæ Latr., according to Reaumur, six months[557]; that of Phalæna urticata nine months[558]; and that of Cimbex lutea, according to De Geer, sometimes eighteen months[559]. Brahm observes, that such larvæ of the double-brooded moth, Hepialus Testudo, as form their cocoons in autumn, do not become pupæ until the following spring; while those which form them in summer undergo this change in a few days[560]. From this fact it might be conjectured, that the degree of heat prevailing at the time the insect incloses itself determines the period of the pupa's appearance; but this supposition seems contradicted by what Reaumur observed of a brood of the larvæ of Phalæna urticata, just mentioned, which, though they formed themselves cocoons in September, did not become pupæ till the June following[561]. I am unable, therefore, to assign any plausible cause for these extraordinary variations. The difficulty of comprehending how animals before so voracious can live so long without food may be partly surmounted, by adverting to the circumstance of its having attained its full growth, and laid up a store of nutriment for the development of the perfect insect. It is consequently no more wonderful that it should not have need of any further supply without casting off its upper integument, than that it should not eat after having done so and become a pupa.

FOOTNOTES:

[206] De Geer vii. 197.Return to passage

[207] De Geer vii. 197.Return to passage

[208] Ibid. 85.Return to passage

[209] Epist. lxvii. 1694. 390.Return to passage

[210] Enum. Ins. Austr. 575.Return to passage

[211] N. Dict. d'Hist. Nat. i. 74.Return to passage

[212] De Geer vii. 576.Return to passage

[213] Ibid. 584.Return to passage

[214] Considerat. Géner. 21. Horæ Entomolog. 353.Return to passage

[215] De Geer, Ibid. Mr. W. MacLeay observes of the Chilopoda, or Centipedes, that they moult in the manner of Crustacea. ubi supr. 352.Return to passage

[216] De Geer iii. 549. The figure of the forceps in De Geer (Ibid. t. xxv. f. 21) is not quite correct. The styles do not taper to a point, but are filiform and acute.Return to passage

[217] Compare De Geer iii. t. xviii. f. 2 and 12. q.Return to passage

[218] See above, VOL. II. p. 401.Return to passage

[219] PLATE XVI. FIG. 4. c. Reaum. v. t. xix. f. 16. De Geer ubi supr. t. xxxii. f. 26. According to Reaumur, the larva as well as the pupa of Chermes Ficus has wing-cases (iii. 353).Return to passage

[220] These are in the female sex of some Coleoptera, as Lampyris, &c. which retain in the perfect state nearly the same form which they had when larvæ. The larvæ of some Staphylini are not very dissimilar in form to the perfect insect.Return to passage

[221] The larvæ described in the first Section, which resemble the imago, are usually covered with a skin not materially different from that of the insect in that state.Return to passage

[222] Huber Fourmis. 73; N. Dict. d'Hist. Nat. vi. 250.Return to passage

[223] Reaum. v. 40. t. vi. f. 4-15.Return to passage

[224] Müller, the Danish zoologist, relates, that he once met with a papilio which, with the true wings of the genus, had a head without antennæ or tongue, furnished with mandibles; and, in short, that of a true caterpillar. It was a female, which deposited eggs that proved barren. If this solitary instance was not a mistake, is it possible that some parasitic larva had devoured only the inclosed head of the butterfly, or so injured it that it could not reject the hard skin of the larva, and yet not be destroyed?Return to passage

[225] The only larvæ which have a visible distinct neck are those of some Dytisci, Staphylini, and a few others, in which this part is quite distinct: proving the erroneousness of the opinion of those German entomologists, who consider the thorax as analogous to the neck of other animals, and hence call it Halsschild. In some lepidopterous larvæ, however, as in that of Pieris Brassicæ, though no visible neck presents itself, one is very perceptible when the insect stretches the head forward considerably. Reaum. i. 460.Return to passage

[226] PLATE XVII. FIG. 13.Return to passage

[227] Reaum. v. t. vi. f. 7. i. c.Return to passage

[228] In fact, in almost all Lepidopterous larvæ the head may be regarded as divided into two lobes or eye-shaped portions, which include in the angle formed by their recession anteriorly from each other, the nasus (clypeus F.), the labrum, and other instruments of manducation. Posteriorly these lobes generally come into contact; but I have a specimen in which there is a narrow space between them.Return to passage

[229] Ins. Surinam. t. xvii.Return to passage

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

[231] Ibid. t. xxxii.Return to passage

[232] Ibid. t. viii.Return to passage

[233] Ibid. t. xxiii.Return to passage

[234] Ibid. t. xiv.Return to passage

[235] I purchased this singular caterpillar from the collection of the late Mr. Francillon, with his other exotic larvæ; but without any indication of the fly to which it belonged.Return to passage

[236] De Geer vi. 352.Return to passage

[237] De Geer iv. 66. ii. 922.Return to passage

[238] De Geer v. 170.Return to passage

[239] De Geer says, he could not make out the number of eyes of the larva of the whirlwig (Gyrinus): probably, as in that of Dytiscus, there are six. iv. 362. 385.Return to passage

[240] Pez. 188.Return to passage

[241] ii. 923, t. xxxvi. f. 1, b b. Fabr. Philos. Ent. 60.Return to passage

[242] Lyonnet 41. t. ii. f. 1. c.Return to passage

[243] De Geer vi. 307.Return to passage

[244] Ibid, ii. t. xvi. Comp. f. 2 a a with f. 14 a a.Return to passage

[245] In the larva of Cicindela there are six palpi, as in the perfect insect.Return to passage

[246] Lyonnet, t. i. f. 7. E. In the larva of Callidium violaceum, however, this part is of a singular shape, being orbicular. Kirby Linn. Trans. v. t. xii. f. 12. a.Return to passage

[247] It is affirmed (N. Dict. d'Hist. Nat. vii. 333) that the larvæ of those Coleoptera that live in carcases have mandibles almost membranous: those, however, of that of Silpha rugosa are horny and hard.Return to passage

[248] Lyonnet, t. ii. f. 1. D D, and f. 2, 3, 4.Return to passage

[249] Kirby in Linn. Trans. v. t. xii. f. 7 b.Return to passage

[250] Cuvier Anat. Comp. iii. 322.Return to passage

[251] Reaum. vi. 340.Return to passage

[252] The larva of Cicindela campestris has mandibles of this description. PLATE XVII. FIG. 13. c´.Return to passage

[253] See above, VOL. II. 275--.Return to passage

[254] Reaum. v. 9. t. i. f. 4. c c. l l.Return to passage

[255] Traité Anatom. t. ii. f. 1. H H.Return to passage

[256] Reaum. ii. t. 40. f. 4.Return to passage

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

[258] Ibid. iv. t. xi. f. 16. p p.Return to passage

[259] Linn. Trans. v. t. xii. f. 10.Return to passage

[260] Cuvier Anat. Comp. iii. 323.Return to passage

[261] De Geer iv. t. xv. f. 9. b b. The exterior and interior palpi are both represented in this figure.Return to passage

[262] Reaum. vi. t. xxxvii. f. 5. e e.Return to passage

[263] Ibid. i. 125.Return to passage

[264] PLATE XXI. FIG. 9. The organ with which the larvæ of Hemerobius, Myrmeleon, and Hydrophilus, spin their cocoons, is situated in the anus. The spinneret of the Cossus is figured by Lyonnet Anatom. t. ii. f. 1. I. and fig. 9.Return to passage

[265] De Geer vi. 370. This species (Tipula Agarici seticornis De Geer) has two separate spinnerets. t. xx. f. 8. m m.Return to passage

[266] Lyonnet 55--.Return to passage

[267] Reaum. iv. 166.Return to passage

[268] Reaum. v. 155.Return to passage

[269] Ibid. vi. t. xxxvii. f. 7. b p.Return to passage

[270] Ibid. m e e.Return to passage

[271] Ibid. f. 6. p.Return to passage

[272] Ibid. Compare f. 4 with f. 6, 7.Return to passage

[273] Ibid. t. xxxvi. f. 12. s u e.Return to passage

[274] Ibid. n e, and xxxviii. f. 7, d c.; De Geer ii. t. xix. f. 17. d g.Return to passage

[275] Reaum. vi. t. xxxvii. f. 4-6. 8.Return to passage

[276] Ibid. t. xxxviii. First joint f. 8. b f p.; jaws f. 7. c d.; opening o, Ligula, f. 6. l.Return to passage

[277] De Geer ii. f. 17. Jaws g g; claw d; tooth h.Return to passage

[278] Ibid. 674.Return to passage

[279] Ibid. ii. 674.Return to passage

[280] Reaum. iv. 376.Return to passage

[281] N. Dict. d'Hist. Nat. xii. 64.Return to passage

[282] Anat. Comp. iii. 322.Return to passage

[283] At first in the Dytisci they appear to have five joints; but, as I before observed, the first joint must be regarded as representing the maxilla.Return to passage

[284] Lyonnet Anatom. 55, 58.Return to passage

[285] De Geer v. 203.Return to passage

[286] De Geer iv. 5. Legs of this kind are figured PLATE XXIII. FIG. 7.Return to passage

[287] In the larva, however, of Sialis, or some kindred genus, in which, like those of Scolopendra, the prolegs are jointed, a pair distinguishes each abdominal segment. See Reaum. iv. t. xv. f. 1, 2. Compare De Geer ii. t. xxiii. f. 11.Return to passage

[288] See above, VOL. II 286--.Return to passage

[289] Ibid. 288.Return to passage

[290] Lyonnet Anatom. t. iii. f. 8. Coxa B. Trochanter C. Femur D. Tibia E. Tarsus F. Claw G.Return to passage

[291] De Geer iv. t. xiii. f. 20; and t. xv. f. 16.Return to passage

[292] Ibid. ii. t. xvi. f. 5, 6, 7. d e: and t. xix. f. 4. c f g h.Return to passage

[293] The larva of a scarce moth (Stauropus Fagi. See PLATE XIX. FIG. 4) is an exception to this. The first pair of its legs are of the ordinary stature, but the two next are remarkably long, and so thin and weak as to be unable to bear the body. Pezold. 119. Another minute caterpillar described by Reaumur has the third pair of the legs apparently fleshy and singularly incrassated at the apex into a pyriform figure, terminated by a pair of claws. This conformation is for some particular purpose in the economy of the animal, since they are the most busily employed of all in arranging the threads of her web. Reaum. ii. 258. In the larva of a geometer (Geometra lunaria) the third pair are remarkably long. Illig. Mag. 402. In that of another moth, according to Kuhn (Naturf. xvi. 78. t. iv. f. 3), the third pair of the fore-legs is remarkably incrassated, being twice as thick and long as the other pair, though consisting of the same number of joints, the last of which has claws.Return to passage

[294] On the legs and prolegs see also what is said above, VOL. II. p. 286--.Return to passage

[295] In some few instances these legs are dorsal. Ibid. 281.Return to passage

[296] The claws or crotchets, though general, are not universal, in Lepidopterous larvæ. An exception is furnished to the rule by the singular limaciform ones of Hepialus Testudo and Asellus of Fabricius, two moths forming Haworth's genus Apoda, which have no distinct prolegs, but in their stead a number of small transparent shining tubercles without claws. The larva also of one of the subcutaneous moths first discovered by De Geer in the leaves of the rose (i. 446), but whose history is fully given by Goeze, Naturf. xv. 37-48, (who has satisfactorily ascertained that it is the true larva of a Tinea of Linné, but of a different habit from that of most subcutaneous ones), has no true legs, and eighteen prolegs without any claws. Another subcutaneous larva, for the history of which we are indebted to M. Godeheu de Riville, is according to him entirely deprived of legs of any kind (Bonnet ix. 196--.); as is another of the same tribe that feeds on the poplar, an account of which is given by Goeze Naturf. xiv. 105.Return to passage

[297] PLATE XXIII. FIG. 7. See also below, p. 137.Return to passage

[298] Lyonnet Anatom. 84. t. iii. f. 11, 12.Return to passage

[299] Hist. Vermium, 130.Return to passage

[300] PLATE XXIII. FIG. 1.Return to passage

[301] PLATE XXIII. FIG. 18.Return to passage

[302] Account of Locust-tree Insects, 69.Return to passage

[303] Reaum. iv. 443. t. xxx. f. 6. l l. t. xxii. f. 6. l l.Return to passage

[304] De Geer vi. 383. and 137. t. viii. f. 8, 9.Return to passage

[305] See above, VOL. II. p. 278. De Geer ubi supr. 376.Return to passage

[306] Reaum. iv. 184. t. xv. f. 12. c c.Return to passage

[307] De Geer v. 203.Return to passage

[308] See above, p. 110, 114.Return to passage

[309] Some few subcutaneous larvæ have more, as that, before mentioned, observed by De Geer in the leaves of the rose; which has eighteen prolegs, and no true ones.Return to passage

[310] De Geer ii. t. xl. f. 15, 16. Bergman has added to these four classes of the larvæ of saw-flies, a fifth; the insects belonging to which, he affirms, though they have sixteen prolegs, are without the anal pair. Ibid. 931. But as neither De Geer nor Reaumur ever met with one of this description, it is probable he was mistaken. Reaumur thought he had seen one with eighteen prolegs upon Erysimum alliaria (v. 91), but he does not speak positively.Return to passage

[311] De Geer v. 288.Return to passage

[312] De Geer iv. 157.Return to passage

[313] Ibid. v. 36. t. ii. f. 11.Return to passage

[314] See above, VOL. I. p. 171.Return to passage

[315] De Geer v. 228.Return to passage

[316] Ibid. 233.Return to passage

[317] See above, VOL. II. p. 281.Return to passage

[318] De Geer vi. 388.Return to passage

[319] Ibid. 389.Return to passage

[320] Reaum. v. t. v. f. 10.Return to passage

[321] Ibid. 31. This larva has also a pair of pediform processes at the anus, surrounded at the end with claws (t. v. f. 4, 5, s s), which he saw the animal use in locomotion; but which he suspects to be respiratory organs (Ibid. 33), which Latreille asserts they are. Gen. Crust. et Ins. iv. 249.Return to passage

[322] De Geer Ibid. t. xxiv. f. 15-17.Return to passage

[323] Ibid. 383.Return to passage

[324] Ibid. 111. t. vi. f. 14-16.Return to passage

[325] Merian Ins. Sur. t. xx.Return to passage

[326] Ibid. t. xxxiv.Return to passage

[327] I have a caterpillar, I believe from Georgia, in which this horn is nearly an inch long, filiform, slender, and tortuous.Return to passage

[328] PLATE XVIII. FIG. 12. c.Return to passage

[329] That of Sphinx Iatrophæ L. appears to be jointed, at least it is moniliform. Merian Surinam. t. xxxviii. Compare also t. iii.Return to passage

[330] N. Dict. d'Hist. Nat. vi. 252.Return to passage

[331] Schellenberg Entomolog. Beytr. t. 1.Return to passage

[332] Smith's Abbott's Insects of Georgia, t. xiii.Return to passage

[333] De Geer ii. 507. t. xi. f. 16. m n. t. xiv. f. 7.Return to passage

[334] N. Dict. d'Hist. Nat. vi. 256.Return to passage

[335] See above, VOL. II. p. 244--.Return to passage

[336] PLATE XIX. FIG. 1. a.Return to passage

[337] Reaum. i. t. xxx. f. 2. N. Dict. d'Hist. Nat. xxiv. 490, 497--.Return to passage

[338] Ray says he found it feeding on common fennel, about Middleton in Yorkshire: Lett. 69. The indefatigable Mr. Dale recently found many in the neighbourhood of Whittlesea-mere, feeding on Selinum palustre. It will also eat the wild carrot.Return to passage

[339] This gentleman was remarkable for the admirable manner in which he prepared caterpillars, so as scarcely to differ from life.Return to passage

[340] Reaum. i. 92.Return to passage

[341] Bonnet ii. 84--. iii. 1.Return to passage

[342] See above, VOL. II. 251--.Return to passage

[343] Bonnet ii. 88.Return to passage

[344] De Geer ii. 507. t. xi. f. 16. c.Return to passage

[345] Rös. iv. 162.Return to passage

[346] De Geer i. 322--. See PLATE XIX. FIG. 2. a a.Return to passage

[347] Reaum. ii. 275. t. xxii. f. 3.Return to passage

[348] Ibid. 276. t. xxii. f. 4, 5.Return to passage

[349] Ins. Surinam. t. vii. Nymphalis Amphinome xxiii. Morpho Teucer t. xxxii. Papilio Cassiæ.Return to passage

[350] This is not, however, universally the case, for the caterpillar of a Geometer described by Reaumur (ii. 363. t. xxix. f. 8.) (G. amatoria) has a pair of fleshy anal horns, terminating, it should seem from his figure, in a minute hook that the animal uses as a forceps; which has at the same time the anal legs, of which indeed these horns seem to be appendages.Return to passage

[351] Sepp. iv. t. l. f. 6-8.Return to passage

[352] PLATE XIX. FIG. 5. a b. Sepp. iv. t. xxi. f. 4-7.Return to passage

[353] Rös. iii. 69.Return to passage

[354] PLATE XVII. FIG. 13. c.Return to passage

[355] N. Dict. d'Hist. Nat. vii. 95.Return to passage

[356] De Geer v. 170-- t. v. f. 19-23. Compare Reaum. iii. 235--.Return to passage

[357] PLATE XIX. FIG. 11. a. De Geer vi. 137. Reaum. iv. 482.Return to passage

[358] Reaum. iv. t. xiv. f. 9, 10.Return to passage

[359] Reaum. v. 32. t. v. f. 3-5. Latr. Gen. Crust. et Ins. iv. 249.Return to passage

[360] De Geer ii. 1031. t. xl. f. 13, 14. k k.Return to passage

[361] N. Dict. d'Hist. Nat. x. 430.Return to passage

[362] De Geer ii. 697. t. xxi. f. 4, 5. b b b.Return to passage

[363] Reaum. v. t. vi. f. 7. n.Return to passage

[364] PLATE XVIII. FIG. 2.Return to passage

[365] Reaum. ii. t. xxv. f. 20.Return to passage

[366] See above, VOL. II. p. 245--.Return to passage

[367] Reaum. iii. 384. vi. 366. t. xxxii. f. 7, 8.Return to passage

[368] Rös. iii. t. lxviii. f. 1. Meinecken Naturf. vi. 120.Return to passage

[369] Ibid. xiii. 175.Return to passage

[370] In the larva of Tenthredo Cerasi L., and some others, no traces of segments are to be seen; and in many coleopterous and dipterous ones the folds of the skin prevent the segments from being distinctly perceptible.Return to passage

[371] Reaum. ii. 361. In the larva of a small common moth often met with in houses (Aglossa pinguinalis), every segment is divided into two parts, and underneath has two deep folds, by means of which these two parts can separate to a certain point, or approach again, according to circumstances. Thus Providence has enabled them to prevent their spiracles from being stopped by the greasy substances on which they often feed. N. Dict. d'Hist. Nat. i. 208.Return to passage

[372] See above, p. 110.Return to passage

[373] N. Dict. d'Hist. Nat. xvii. 329.Return to passage

[374] Hor. Entomolog. 285. 397--. 422. 462--. &c.Return to passage

[375] Ibid. 399-401.Return to passage

[376] Hor. Entomolog. 423.Return to passage

[377] See above, p. 23.Return to passage

[378] The Intestinaux cavitaires of Cuvier, and the Epizoaria of Lamarck. See Hor. Entomolog. 286--.Return to passage

[379] Hor. Entomolog. 422. comp. 463. Mr. MacLeay's idea of the larva of Meloe is taken from the animal which Frisch, Goedart, and De Geer imagined to be such; but upon this opinion there rest great doubts. (See Kirby Mon. Ap. Angl. ii. 168, and Latreille N. Dict. d'Hist. Nat. xx. 109.) At p. 464 he gives also Mordella and many Heteromera as having Thysanuriform larvæ. He thinks, that probably that of Clerus is of the same description; to which he suspects that many of Latreille's Malacoderma likewise belong.Return to passage

[380] PLATE XVIII. FIG. 1. as to the thoracic shield.Return to passage

[381] May 27, 1822. This day, T. Allen, Esq. F.L.S. brought me in a phial a vast number of the little insect which Goedart, Frisch, and De Geer took for the larva of Meloe Proscarabæus, which he found on the leaves of Achillea Millefolium. These little animals were coursing each other with wonderful velocity over the sides of the phial. To assist them in their motions, they applied to the surface of the glass the end of their abdomen, using it, like many larvæ of Coleoptera, as a seventh leg. This circumstance excited a suspicion in the minds of both Mr. MacLeay sen., then visiting me, and myself, that after all they might be coleopterous larvæ. One, amongst other circumstances, however, seemed to militate strongly against this opinion; namely, that in this infinite number none appeared to differ in size.Return to passage

[382] PLATE XVII. FIG. 13.Return to passage

[383] Ibid. FIG. 12.; PLATE XVIII. FIG. 4, 11, 13, &c.Return to passage

[384] PLATE XVIII. FIG. 3, 9.Return to passage

[385] PLATE XIX. FIG. 8.Return to passage

[386] Ibid. FIG. 3. Reaum. v. 97. t. xii. f. 17, 18.; De Geer ii. 1004. t. xxviii. f. 12.Return to passage

[387] See above, p. 110, 114, 138, 142.Return to passage

[388] PLATE XVIII. FIG. 7.Return to passage

[389] PLATE XVIII. FIG. 5.Return to passage

[390] PLATE XIX. FIG. 9.Return to passage

[391] PLATE XVIII. FIG. 2.Return to passage

[392] Hor. Entomolog. 465.Return to passage

[393] De Geer iv. 66. t. ii. f. 5-8.Return to passage

[394] Ibid. t. xiii. f. 16-19. A very singular larva, which preys upon that of Aleyrodes proletella Latr., if Reaumur's figure be correct (ii. t. xxv. f. 18-20), is of a perfect Chilopodiform type, the abdominal legs being represented by a tubercle crowned by a bristle: yet even this, which turns to a minute beetle (Ibid. f. 21), has some tendency to the Anopluriform type.Return to passage

[395] "Squilla insectum a squilla pisce parum differt." Mouffet, 319.Return to passage

[396] A remarkable difference obtains between the larva of the wire-worm and that of Elater undulatus. In the former, the last segment is longer than the preceding one, terminating in a small acute mucro at the apex, with a deep cavity, perhaps a spiracle, on each side, at the base. In the latter, this segment is shorter than the preceding one, forming above a nearly circular plate; the margin of which is a little elevated, and armed on each side with three teeth, and at the apex with a pair of furcate recurved horns, and without any basal spiracle. De Geer iv. 156. t. v. f. 25. I have a similar larva, but not the same species.Return to passage

[397] Hor. Entomolog. 397.Return to passage

[398] Ibid. 399.Return to passage

[399] Ibid. 438. Note *.Return to passage

[400] Traité Element. ii. 35. n. 577.Return to passage

[401] Trans. Linn. Soc. vii. 66. t. vi. f. 3.Return to passage

[402] Compare De Geer iii. t. xi. f. 3. and t. xvii. f. 14. &c.Return to passage

[403] Ibid. t. i. f. 4, 9. t. ii. f. 15. t. ix. f. 4.Return to passage

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

[405] Compare PLATE VI. FIG. 6. with FIG. 12 c, d, d.Return to passage

[406] De Geer ii. t. xxi. f. 4, 5.Return to passage

[407] Swamm. Bibl. Nat. t. xiii. f. 1.Return to passage

[408] Hor. Entomolog. 438.Return to passage

[409] See above, VOL. II. p. 256.Return to passage

[410] De Geer ii. t. xxiii. f. 9-14. Comp. Reaum. iv. t. xv. f. 1, 2.Return to passage

[411] De Geer ii. t. xiv. f. 7. &c. The caterpillar of P. G. Scratiotata L. like those of Phryganeæ, has these respiratory threads. Ibid. i. t. xxxvii. f. 2-6. De Geer has described the larva of a Phryganea L. which is without any respiratory threads, ii. 569. t. xv. f. 10.Return to passage

[412] Hor. Entomolog. 401. Montagu in Linn. Trans. vii. 67.Return to passage

[413] Ins. Surinam. t. xxviii. Compare Ibid. t. xix. right-hand figure.Return to passage

[414] PLATE XVIII. FIG. 10.Return to passage

[415] Swamm. Bibl. Nat. t. xxxix. PLATE XIX. FIG. 13.Return to passage

[416] Lyonnet 69--.Return to passage

[417] Surinam, t. lvii. right-hand figure.Return to passage

[418] Sepp iv. t. ii. f. 3. t. xvi. f. 2, 3.Return to passage

[419] N. Dict. d'Hist. Nat. vi. 254.Return to passage

[420] PLATE XIX. FIG. 6. One of these larvæ was taken at Melville Island. See Parry's Voyage, Appendix No. x. 37.Return to passage

[421] Sepp. iv. t. viii. f. 4. Some species have three, others four, and others even five of these brushes. N. Dict. d'Hist. Nat. vi. 255.Return to passage

[422] Ibid. Merian Eruc. xxxiv. upper left hand figure.Return to passage

[423] Merian Ins. Surinam. t. lx.Return to passage

[424] Ibid. t. xl.Return to passage

[425] See above, VOL. I. p. 238.Return to passage

[426] De Geer iv. 207. t. viii. f. 4-6.Return to passage

[427] Ins. Sur. t. xix. right hand caterpillar.Return to passage

[428] Ibid. xli.Return to passage

[429] PLATE XVIII. FIG. 13.Return to passage

[430] Ins. Sur. t. xxix.Return to passage

[431] Ibid. t. vii. liii.Return to passage

[432] Smith's Abbott's Ins. of Georg. Pref. vi.Return to passage

[433] Prodromus Entomology.Return to passage

[434] Ins. Sur. t. xliii. The figure represents only the two spines near the head as thus circumstanced.Return to passage

[435] Reaum. v. t. xii. f. 8, 14. PLATE XVIII. FIG. 11.Return to passage

[436] See above, VOL. II. p. 238. This, with B. imperatoria, &c. in the modern system, should form a genus.Return to passage

[437] Ins. Sur. t. xlviii. right hand figure.Return to passage

[438] Ibid. t. xi.Return to passage

[439] Ibid. t. xxiii.Return to passage

[440] Ibid. t. xxix.Return to passage

[441] Reaum. v. 95.Return to passage

[442] Huber Mœurs des Fourmis, 79.Return to passage

[443] See above, VOL. II. p. 276--.Return to passage

[444] Reaum. v. 72. t. ix. f. 2-4.Return to passage

[445] Rös. t. 211.Return to passage

[446] See above, VOL. I. p. 29, 198--.Return to passage

[447] De Geer iii. 111. Comp. 121. It would be as well to adopt the French word flocon, instead of locks or flocks, which strictly mean very different things.Return to passage

[448] vii. 604. t. xliv. f. 26.Return to passage

[449] Fn. Germ. Init. xxxvi. 21.Return to passage

[450] Syst. Rhyng. 311. 29.Return to passage

[451] N. Dict. d'Hist. Nat. ix. 554.Return to passage

[452] Natural History of the Slug-worm, 7.Return to passage

[453] Ins. Surinam. t. xv. xvii.Return to passage

[454] The larvæ of Carabus L. form one, being generally black.Return to passage

[455] Annales de Chimie ii.Return to passage

[456] Wien. Verz. 219.Return to passage

[457] Wien. Verz. 4.Return to passage

[458] Reaum. v. 92.Return to passage

[459] Ins. Surinam. t. xi.Return to passage

[460] ii. 1017.Return to passage

[461] De Geer i. 57.Return to passage

[462] Ibid. 58. Reaum. i. t. xxxix. f. 13, 14.Return to passage

[463] De Geer ii. 400.Return to passage

[464] See above, VOL. I. Letters xii. xiii.Return to passage

[465] Bonnet (ii. 18) mentions, that the young larvæ of a butterfly (Pieris Cratægi), after devouring the exuviæ of the eggs from which they were hatched, gnawed those which were not so: not, however, so as to destroy the included animal, but rather to facilitate its egress. Those also of Coccinella bipunctata which I lately bred from the egg, as soon as hatched began to devour the unhatched ones around them, which they seemed to relish highly. I am inclined to believe, however, that this unnatural procedure was to be attributed to the circumstance of the female not having had it in her power to place her eggs in the midst of Aphides, their proper food.Return to passage

[466] N. Dict. d'Hist. Nat. xx. 359.Return to passage

[467] In the human species, after certain fevers a simultaneous and total moult, if the term may be so applied, takes place. I experienced this myself in my boyhood; when convalescent from Scarlatina, the skin of my whole body, or nearly so, peeled off.Return to passage

[468] The translator, more ignorant of natural history than his author, has turned the "linguis micat ore trisulcis" of Virgil, into "darts his forky sting."Return to passage

[469] VOL. I. p. 70.Return to passage

[470] See above, p. 52--.Return to passage

[471] Cuvier Anat. Comp. ii. 596. N. Dict. d'Hist. Nat. xxvi. 165.Return to passage

[472] Cuvier Ibid. 624.Return to passage

[473] Reaum. i. 182.Return to passage

[474] N. Dict. d'Hist. Nat. vi. 290.Return to passage

[475] Those Diptera whose metamorphosis is coarctate (VOL. I. p. 67), bees, the female Cocci, &c. do not cast their skin in the larva state. Reaum. iv. 364. N. Dict. d'Hist. Nat. xx. 365.Return to passage

[476] N. Dict. d'Hist. Nat. vi. 289. xx. 372. Cuvier Anat. Comp. ii. 548. M. Cuvier (Ibid. 547.) asserts, that most Papiliones and Bombyces moult seven times.Return to passage

[477] Œuvr. ii. 71.Return to passage

[478] Reaum. ii. 75.Return to passage

[479] Bibl. Nat. E. Trans. i. 135. col. B. t. xxvii. f. 6.Return to passage

[480] Œuvres, viii. 303.Return to passage

[481] Entwickelungsgeschichte, &c. 34, 88. Swammerdam on the contrary affirms, that "on the hinder part of the cast skin where it is twisted and complicated, whoever accurately examines the skin itself may still observe the coat that was cast by the intestinum rectum." Ubi supr. 136. col. A.Return to passage

[482] N. Dict. d'Hist. Nat. vi. 290Return to passage

[483] Reaum. iv. 604.Return to passage

[484] Ibid. 364. N. Dict. d'Hist. Nat. xx. 365. Huber Fourmis 78. M. Huber does not say expressly that the grubs of ants do not change their skin; but his account seems to imply that they change it only previously to their metamorphosis.Return to passage

[485] Lyonnet 11.Return to passage

[486] N. Dict. d'Hist. Nat. vi. 290.Return to passage

[487] De Bombycibus, 68.Return to passage

[488] Opusc. i. 27.Return to passage

[489] Linn. Trans. x. 399.Return to passage

[490] N. Dict. d'Hist. Nat. vii. 129.Return to passage

[491] As the larvæ of Ephemeræ usually live in the submerged part of the banks of rivers, perhaps they may be regarded as following the economy of subterranean terrestrial larvæ.Return to passage

[492] A caterpillar nearly answering to the description of that of Bombyx camelina, which I found upon the hazel, after a few days produced sixteen grubs of some Ichneumon. At first these grubs were green, but they became gradually paler; and after a day or two became pupæ. But I mention this circumstance here for another reason: upon examining them after this last occurrence, I observed that they adhered to the lid of the box in which I kept the larva, arranged somewhat circularly; and at a little distance from the anus of each was a pea-green mass, consisting of about eight oval granules, which appeared like so many minute eggs. These were the excrement evacuated by each grub previously to its becoming a pupa. The appearance of this little group, with their verdant appendage, formed a curious spectacle: they are still pupæ, July 30, 1822.Return to passage

[493] Except some species of Polyammatus Latr. (Thecla, Argynnis F.), P. Argiolus, Corydon, &c., and Hesperia Rubi, Betulæ F., &c. Some of the larvæ of the former become pupæ within the stalk of some plant, or partly under the earth: those of the latter usually in a leaf to which the abdomen is fastened by various threads. These last are the rouleuses of the butterfly-tribe, living, like some moths, in leaves that they have rolled up. N. Dict. d'Hist. Nat. xxiv. 499.Return to passage

[494] PLATE XXIII. FIG. 1. a.Return to passage

[495] PLATE XXIII. FIG. 8. a.Return to passage

[496] Bonnet is of opinion that this twirling process is not with any view to get rid of the exuviæ, but is caused only by the irritation occasioned by the spines of the skin of the caterpillar when they touch that of the pupa. Œuv. ii. 109.Return to passage

[497] For the above account see Reaum. i. Mem. x. xi.Return to passage

[498] N. Dict. d'Hist. Nat. vi. 291--.Return to passage

[499] De Bombyc. 24.Return to passage

[500] i. 498.Return to passage

[501] De Bombyc. 43.Return to passage

[502] N. Dict. d'Hist. Nat. vi. 294.Return to passage

[503] Lesser. L. ii. 150, note 22. Boyle says an English lady found that the silk of a single cocoon would extend 300 English leagues or 900 miles. But this must be a mistake.Return to passage

[504] Reaum. i. 555--.Return to passage

[505] PLATE XVII. FIG. 5. b.Return to passage

[506] De Geer i. t. xxxii. f. 3-6.Return to passage

[507] De Geer i. 463--.Return to passage

[508] Reaum. ii. Mem. xi. Comp. De Geer ii. 162. Reaum. ii. 424.Return to passage

[509] B. Catax--Pupa arcte folliculata. Fab.Return to passage

[510] Travels in Greece, 285.Return to passage

[511] See above, VOL. I. p. 476--.Return to passage

[512] Merian Surinam. t. xv.Return to passage

[513] Reaum. ii. t. xxiii. f. 5.Return to passage

[514] Sepp. iv. t. viii. f. 5.Return to passage

[515] Reaum. i. t. xliv. f. 2.Return to passage

[516] PLATE XVII. FIG. 7.Return to passage

[517] I have a black one from Mr. Francillon's cabinet.Return to passage

[518] N. Dict. d'Hist. Nat. vi. 294.Return to passage

[519] See above, VOL. II. p. 298--.Return to passage

[520] Reaum. ii. 436.Return to passage

[521] Reaum. i. 503.Return to passage

[522] Peck on Locust-tree Insects, 69.Return to passage

[523] Bonnet ii. 260.Return to passage

[524] Sepp. iv. t. ii. f. 4.Return to passage

[525] Brahm. Ins. Kal. 289.Return to passage

[526] PLATE XVII. FIG. 8.Return to passage

[527] The thick cocoons of Attacus Paphia, Polyphemus, &c. are also thus fastened between leaves.Return to passage

[528] Merian Europ. ii. t. ix.Return to passage

[529] Reaum. ii. 284.Return to passage

[530] Ibid. i. 524.Return to passage

[531] Bonnet ii. 297.Return to passage

[532] Ibid. ix. 181.Return to passage

[533] Reaum. v. 102.Return to passage

[534] Ibid. iv. 269.Return to passage

[535] De Geer ii. 1084. Comp. Ray Hist. Ins. Præf. xi. It is the opinion of M. P. Huber, that in this case the naked pupæ are deprived of their cocoons by the neuters: he states, indeed, that he has often seen them pulled off by them, and also by those of F. canicularia; and he seems to think that these larvæ are never developed. Mœurs des Fourmis, 84. note 1.Return to passage

[536] II. viii. 16.Return to passage

[537] Linn. Trans. vii. t. ii. f. 5, 6.Return to passage

[538] Wien. Verz. I possess a cocoon of this kind from New Holland, even now quite solid, and retaining its form. No silk appears to have been used in its composition.Return to passage

[539] Reaum. i. 579.Return to passage

[540] Ibid. vi. 368.Return to passage

[541] Ibid. i. 542.Return to passage

[542] Ibid. 543.Return to passage

[543] Linn. Trans. i. 196.Return to passage

[544] Reaum. i. 545--.Return to passage

[545] Pyral. 8. 3. t. iii. f. 16.Return to passage

[546] See above, VOL. I. p. 172--.Return to passage

[547] Reaum. ii. 491.Return to passage

[548] Reaum i. 540.Return to passage

[549] See above, VOL. I. 167--. II. 264.Return to passage

[550] See above, VOL. I. p. 67.Return to passage

[551] N. Dict. d'Hist. Nat. xvi. 269--. xxii. 76.Return to passage

[552] Reaum. iv. 32. The author here quoted asserts that the grub of Ichneumon Larvarum L. retains its skin, which, he says, is so transparent that the form of the nymph can be seen through it. Ibid. ii. 447. De Geer, however, found that this really did cast its skin, which is so transparent as to be scarcely visible, by pushing it gradually towards the anus, where it soon dries up and cannot then be discovered. De Geer ii. 893--. According to Rösel the same circumstance attends the transformation of Coccinella renipustulata Illig. (C. Cacti Ent. Brit.), which at first perplexed him not a little. It is probable that in this case the retention of the skin was accidental; for some of the grubs of a Mycetophila, the transformation of which I observed, became pupæ within their last skin, while others wholly disengaged themselves from it. The cause of this variation, I conjectured, arose from the former being too weak to extricate themselves from the skin.Return to passage

[553] See above, VOL. I. p. 238. Byrrhus Musæorum belongs to this genus.Return to passage

[554] N. Dict. d'Hist. Nat. ii. 161.Return to passage

[555] Pezold. 102.Return to passage

[556] De Geer i. 339--.Return to passage

[557] Reaum. ii. 423, and iii. 497.Return to passage

[558] Ibid. i. 605.Return to passage

[559] De Geer ii. 941.Return to passage

[560] Brahm Insek. 72.Return to passage

[561] Reaum. ubi supra.Return to passage