INSECTS. 



cf formation of thefe coverings ; but our data are hardly 

 fufficient to refolve it fatisfadorily. " Some obfervations," 

 Jays Cuvier, " fcem to prove that tliere are tellaceous 

 animals, which lofe tlieir (hells cntin-ly at certain periods, 

 and are fupplied with new ones. But this reproduftion 

 might be effeded by developement like that of the an- 

 tler : and if it be alYo a developement, which produces the 

 interior layers of tliofe (liells, which do not drop off, it 

 may be compared to that which forms the inner lamina of 

 the horns of cows,, theep, and other nmiinating mammalia, 

 and alfo to the produftion of the cpidrrmis in all animals : 

 that is to fay, it is a deficcation, a kind of death of a mem- 

 brane, which appeared to have fome fort of organization, as 

 long as it was protefted from the conta:t of the external air, 

 or had not acquired completely its charatterillic folidity. 

 All the hard parts which hold the place of bones in in- 

 vertebral animals feem to be developed in this manner. In 

 the crab and lobfter, for example, that wliich ferves at the 

 fame time for integuments and tlceleton, grows no more 

 when it has once attained its pcrfeft harchiefs ; yet the 

 foft parts flill continue the progrefs of their developement. 

 AVhen they are too much confined by the hard covering, 

 that feparates and is detached : but another is found under 

 it, which was in a llate of formation while the former was 

 detaching itfelf, or, as we may fay, dying. This new co- 

 vering is at firft foft, fenfible, and even vafcular ; but a 

 quantity of calcareous matter, previoufly coUefted in the 

 ftomach, is very foon conveyed to it, hardens it, obllructs 

 the pores and vefTels, and renders it, in ihort, perfectly fimi- 

 lar to that of which it has fupplied the place. Infefts do 

 not acquire their perfecl hardnefs until they have taken 

 their lall form, and have no further change of fkin to un- 

 dergo ; but all the fkins which they had cafl off before, al- 

 though fofter, were dead, and already replaced by others, 

 developed before they were difcharged. Thus all the hard 

 external organs of white-blooded animals, whatever their con- 

 fidence and chemical nature may be, fhould rather be com- 

 pared, in their mode of giowth, to the epidermis, to hoi- 

 low nails, and horns, than to true bones." Lecons d'Ana- 

 tomie comparee, t. I, p. Ii8. 



Efulirmh. — Cr'ullacea and infefts, whether in their larva 

 or perfect ftate, have a true epidermis ; but, as this integn- 

 ment, when it has once become dry and hard, is no longer 

 fufceptible of that extenfion which is necelTary to accom- 

 modate the growth of the animal, it is feparated at certain 

 periods, which are definite in each fpecies, but influenced 

 confiderably by the atmofpherical temperature : the animal 

 quits its ikin, paiTmg out from it as from a ilieath. This 

 procefs is called moulting : the infect, in many cafes, is 

 fe>feral days preparing for it, and fometimes periihes. Moll 

 of tli-: larvae of the papilio and bombyx kinds change their 

 covering feven times before they pafs into the ftate of chry- 

 falis. Tl'.e bombyx caja has ten fuccefllve coverings. 



Ttiis mod fmgular procefs is not analogous to the mere 

 reparation of the cuticle in the human fubjecl ; for the parts 

 ■which are detached in infefts, in many cafes afford altach- 

 nient to the mufcles of the animal. Thus, in the crullacea 

 the whole (keleton is ilied, and this takes place annually. 

 " Thefe frequent moultings," fays Lyonet, " of the cater- 

 pillar of the phalina colTus are the more lingular, niafmuch 

 as the caterpillar does not Cmply change its fkin, but calls 

 its whole external covering, in which we obferve the head, 

 jaws, cornea:, all the fcaly parts compofing the lips, the 

 cirri, the fp inning hole, the antenni, and even the fcaics 

 CDcLfed v.it/)in the head, and affording attachment to feveral 

 mufcles ; alfo the lligmata, the nails, fcales, and hooks of 

 tlie feet, the hairs, the anus, in ihort all the vifible external 



furface of the animal. In difpofing itfelf for this operation, 

 it paffes fome days without taking any nourifhn-cnt ; the 

 miilcles, and other interior organs of the head, are detached 

 from the old cranium, and withdrawn into the neck ; thi-y 

 form a new covering, fimilar to that which they have left, 

 but larger, and at firlt foft. When the new fldn, and all the 

 other parts, which contribute to the covcrinp- of the cater- 

 pillar, are formed, the old one is opened, and the animal 

 withdraws from it by an operation fo much the more difficult 

 in confequence of tlie weaknefs caiifed by the foft llate of 

 the new organs, which will not allow it to act with vigour, 

 nor to take any nourilhment for fome days. 



"The catcrpillar,thus newly clothed, exhibits different pro- 

 portions from thofe which it had before moulting ; the head, 

 legs, and all the horny parts are fenfibly larger in comparifon 

 to the reft of the body ; thefe therefore do not increafe after- 

 wards. The body and foft parts of the animal only grow, 

 until they become again too large for their covering, and a 

 new moulting is neceffary.'' Lyonet, Traitc Anatomique 

 dela Chenille, p. 7. 



Rete Mucoj'um. — The place of this organ is held in the 

 cruftacea, by the calcareous fhell, which immediately fnc- 

 ceeds the epidermis ; its colour is commonly a dull green, 

 fometimes red, blue, white, or black. Alcohol, acids, and 

 particularly the application of heat, often produce remark- 

 able changes in thefe colours, as we may obferve in the 

 lobllers brought to our tables. In larvae a layer of mucous 

 fubftance is feen between the epidermis and the mufcles ; 

 and the colours of this vary infinitely in the different fpecies. 

 It is particularly remarkable for its brilliancy in caterpillars, 

 and the larvx of fome hymenoptera ; it gives to their bodies 

 the purell and moft lively tints, of which the (hades and 

 fymmetr)- are admirable. Red, purple, violet, blue, green, 

 yellow, fcarlet, black, S:c. are dillributed in the moil regular 

 and Itriking manner. Probably the brilliant colours of the 

 perfeft infeCts are owing to the mucous body dried and 

 blended with the horny covering. For whillt the lepidoptera 

 are in their chryfalis Itate, the fmall coloured fcales which 

 will afterwards adorn their win^s, appear like the mucofity 

 which is under the (kin of the caterpillars. The colours 

 of the fpiders are alfo owing to this mucous matter, which 

 is found under their fkin, and has the appearance of fmall 

 glandular points marked by different Ihades of colour. But 

 in the culeoptera, and in feveral other orders, the colours 

 feem to refide in the horny tiflue, as thofe of the tellacea do 

 in their calcareous fhells. 



Nothing can be feen in this clafs, which can be compared 

 to the cutis ; there is a peUicle under the fhell of the crullacea, 

 but it is fine, tranlparent, and has very little conlillence. 

 The layer which is feparated from larvae in their moultings, 

 is of the fame nature and thicktiefs as that which is under 

 it and fucceeds. The coverings of the contrafted chryfalifes, 

 fuch as thofe of the lepidoptera and diptera, cannot be re- 

 garded as a true fkin ; it is rather a horny epidermis. I.aflly, 

 in their perfeft llate, infedts have nothing in their coverings 

 which can be compared to cutis. The hairs of infedts feem 

 to be produftions of their epidermis ; for they are difcharged 

 with that in moulting, and are fupplied by new and longer 

 ones. The fcales ol the wings and body in the lepid.>ptera 

 and fome other orders, are fmall horny plates, differently co- 

 loured, implanted in the fkin, and placed one over the other, 

 like tiles in the roof of a building. The plumes of fome 

 infefts are prolongations or flireds of the wings, furnilhed 

 with long hairs on their fides. 



Joinis. — The cruftacea and the proper infedts agree in the 



kind of their articulations ; the particular nature of which 



arifes from their hard ^arts being placed externally to the 



c Bii-ftles^ 



