Part 13

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].