284 THE MECHANICAL FUNCTIONS. 



phosphate of lime. In external appearance their 

 texture approaches nearer to that of horn than to 

 any other animal product; yet in their chemical 

 composition they differ from all the usual forms of 

 albuminous matter. The substance to which they 

 owe their characteristic properties is of a very pe- 

 culiar nature; it has been termed Chitine 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 ori- 

 ginal form. J 



With this substance there is blended a quantity 

 of colouring matter, which has usually a dull brown 

 or black hue. But the colour of the external sur- 

 face 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 re- 

 moved 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 



* Annales de Chimie, torn. 76. 



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



X M. Odier had concluded from his experiments that no nitrogen 

 enters into the composition of this substance. That this conchision 

 has been too hastily adopted has been proved by Mr. Children, who, 

 by pursuing another mode of analysis, found that the chitine of can- 

 tharides contains not less than nine or ten per cent, of nitrogen. 

 See Zoological Journal, i. Ill — 115, 



