-*«.. 



t« 



226 THE MECHANICAL FUNCTIONS. ~ 



of horn than to any other animal product: yet in their che- 

 mical composition they differ from all the usual forms of al- 

 buminous matter. The substance to which they owe their 

 characteristic properties is of a very peculiar nature; it has 

 been termed Chiiine by M. Odier,* and Entomoline by 

 M. Lassaigne.t This substance is found in large quantity in 

 the wings and elytra of coleopterous insects. It is remark- 

 able for not liquefying, as horn does, by the action of heat; 

 and accordingly the integuments of insects, even after having 

 been subjected to a red heat, and reduced to a cinder, are 

 found to retain their original form.:}: 



With this substance there is blended a quantity of colour- 

 ing matter, which has usually a dull brown or black hue. 

 But the colour of the external surface is generally owing to 

 another portion of this matter, which is spread over it like 

 a varnish, and being soluble in alcohol and in ether, may be 

 removed by means of these agents. The colours which are 

 displayed by insects, and which arise from the presence of 

 this latter substance, are often very brilliant, and, as is the 

 case with many other classes of animals, the intensity of the 

 tints is heightened by the action of light. The elytra of 

 tropical insects display a gorgeous metallic lustre depending 

 on the reflection of the prismatic colours; and the same va- 

 riegated hues adorn the scales of butterflies of those regions. 



Hair grows in various parts of the surface of insects. 

 Where the integument is membranous and transparent, these 

 hairs may be distinctly perceived to originate from enlarged 

 roots, or bulbs, and to pass out through apertures in the skin; 

 as is the case with the hair of the larger animals. Their 

 chemical composition, however, is very different, for they 

 are formed of the same substance as the integuments, name- 



• Annales de Chimle, torn. 76. 



I See the work of Straus Durckheim, p. 33. 



t M. Odier had concluded from his experiments that no nitrog-en enters 

 into the composition of this substance. That this conclusion has been too 

 hastily adopted has been proved by Mr. Children, who, by pursuing" another 

 mode of analysis, found that the chitlne of cantharides contains not less than 

 nine or ten per cent, of nitrogen. See Zoological Journal, i. Ill — 115. 



