230 



ANATOMY. 



play into a multitude of shades of colour, which proceeds, according to 

 Roesel *, from their peculiar structure. For whilst the surface of the 

 scales in the majority is flat, there are in these sharp parallel ridges 

 just as if small prisms were affixed to their surface. These prisms are 

 all upon one side of a metallic blue, and on the other side brown, and 

 thus according to the position of the butterfly or of the observer, either 

 the brown or blue side is seen f. 



162. 



With respect to the chemical composition of the common integument, 

 it agrees in general with that of horn, but nevertheless distinguishes 

 itself by some peculiarities of proportion, which may probably arise 

 from its being formed, by not merely the epidermis alone, but by the 

 entire cutis. 



All true horny substances consist essentially of azote (10. 2 

 12. 3), carbon (43. 053. 7), hydrogen (7. 32. 8), and oxygen 

 (29. 3 31. 2). In nitric acid it is dissolved, as also in a heated 

 solution of potass or natron ; muriatic acid, on the contrary, is coloured 

 only by degrees. Boiling water somewhat distends horn, but a 

 continued boiling in closed vessels (Papin's digester) will nearly 

 entirely dissolve it. Dry distillation developes ammonia in com- 

 bination with carbonic acid, as well as other hydrocarbonates, and a 

 peculiar stinking oil, besides which other burnt matter remains 

 which is no further changeable. 



The horny case of insects has as externally, a uniform consistency, 

 so also internally, the same constituents; but it nevertheless dis- 

 tinguishes itself by the admixture of a peculiar substance, viz. 

 chitine or entomeilin, as well as by small portions of phosphate of 

 lime and magnesia. The peculiar character of chitine is its insolu- 

 bility in caustic potass. Exhibited separately, which is very easy by 

 means of treating horny parts in a solution of potass, it appears as an 

 almost colourless transparent substance, which becomes brown in nitric 

 acid, and in the dry distillation produces no carbonate of ammonia, 

 and therefore appears to contain no azote, and it burns in fire 



* Insektenbelustigungen, vol. iii. p. 254. PI. XLIV. f. 5 8. 



f This supposition of Roesel's is erroneous ; the change of colour arises from the 

 reflection of the light, the same as in the buds of the Iris. The scales are merely 

 longitudinally striated. Atitkor's MS. Note. 



