22 THE SKIN OF INSECTS. 



skin of insects is very complicated in its composition- 

 M. Odier, on analysing the wing cases of the cock- 

 chafer, found 1 . Albumen ; 2. Extractive, soluble 

 in water; 3. A brown substance, soluble in potass 

 and insoluble in alcohol ; 4. A coloured oil, soluble in 

 alcohol; 5. Carbonate of potass, phosphate of lime, 

 and phosphate of iron; 6. A particular principle, 

 constituting one fourth of the weight of the wing 

 cases : this principle he named Chitine. 



It is chitine which in reality forms the outer frame 

 or crust of insects. If an insect, such as a cockchafer 

 or a dung beetle, be plunged into a solution of potass 

 and exposed to heat, the crust of the insect is not 

 dissolved and does not change its form. The only 

 change it suffers is the loss of colour ; all the muscles 

 and intestines disappearing, the crust, consisting of 

 chitine, alone remaining. 



Chitine differs therefore from horn, hair, and the 

 human scarf skin, which are soluble in potass. It is, 

 besides, soluble in hot sulphuric acid, does not become 

 yellow by the application of nitric acid, and burns 

 without fusion or losing its form. It does not contain 

 azote. It consequently resembles woody fibre more 

 than any animal substance. 



THE HEAD. 



THE head of insects, though it be represented 

 as composed of three or four pieces, does not in 

 general show the least trace of divisions or rings, like 

 the rest of the body : but, because the rest of the 

 body is composed of rings or pieces, it is conjectured 

 by theory, that the head is also so composed, though 

 we cannot perceive the divisions. 



In the newly hatched insect, the head is often 

 joined to the bo'dy, as in spiders, without any obvious 

 division,which is always apparent in the adult insect; 



