of the Corneous parts of Insects, 107! 



Burns without swelling, and 

 Contains no nitrogen. 



But it was necessary to the end proposed in this analysis, to 

 ascertain whether this horn-like substance be likewise found in the 

 other hard parts of the bodies of insects. I easily satisfied myself 

 by treating the entire animal with caustic potassa ; by this opera- 

 tion the Scarabaeus nasicornis afforded me the carapace very well 

 freed from other matter, and transparent. All the hard parts re- 

 mained in the same state as before, except as regards their transpa- 

 rency ; the hairs, even, were still discernible, which consequently 

 differ in their nature from the hair of vertebrated animals. This 

 method I conceive might be advantageously employed for the pur- 

 pose of examining this covering in an anatomical point of view, 

 and for studying the parts of which it is composed. 



The examination of the Scarabsei taught me that the membranes 

 of the wings are not formed of Chitine, and that the sinews, (ner- 

 vures) which are more solid, ai'e of the same nature as the elytra, 

 that is, that they contain Chitine, animal matter, oil and salts. 

 The parenchymatous matter, which M. M. Thouvenel and Beau- 

 poil, and M. Robiquet found in their analyses of cantharides, is 

 nothing else but Chitine. From these facts, I think we may con- 

 clude, that Chitine is the base of the horny pieces of all insects, 

 of whatever order, and apparently (for I have not made the expe- 

 riment) we may extend this opinion to the arachnides. But is the 

 presence of Chitine limited to this class, or shall we also find it in 

 the Crustacea ? The fact deserves the attention of naturalists and 

 would be well worthy of examination. 



The chemists who have analysed Crustacea, and M. Chevreul the 

 last, have announced the presence of an animal substance in the 

 carapace of those animals without distinctly stating its nature. M, 

 Geoffroy pretends that he has found in the upper layers of this 

 organ the cutis and epidermis of the vertebrated animals, but we 

 shall see that this naturalist was led into error by the external ap- 

 pearance of those parts. 



In order to examine the animal matter of the shell of the Crus- 

 tacea, I macerated the carapace of the common crab, for some 

 days, in water acidulated with muriatic acid. At the expiration 



