THE INTEGUMENT 3 



terrestrial existence for insects and vertebrates. It is these same 

 materials which have made possible the development of wings. 



The ordinary protein of the cuticle, which is tanned to form 

 sclerotin, is called 'arthropodin'. In addition there is always present 

 another protein called k resilin\ This is an elastic substance in which 

 the protein chains are bound together in a uniform three-dimensional 

 network so as to form a perfect rubber. Resilin may be deposited be- 

 tween the chitinous lamellae and provides the elasticity of the cuticle; 

 or it may exist in the pure state to form elastic tendons for muscles 

 connected to the wings or elsewhere. 



In a few aquatic larvae of Diptera there may be deposits of lime in 

 the cuticle and in a few Diptera the puparium may be strengthened 

 with a deposit of lime inside. But insects in general do not harden the 

 cuticle as do many Crustacea by incorporating lime in the form of 

 calcite. It is interesting to note, however, that sclerotin is actually 



fig. 1. — Section of typical insect cuticle 



a, laminated endocuticle; b, exocuticle; c, epicuticle; d, bristle; e, pore-canals; /, duct 

 of dermal gland; g, basement membrane; h, epidermal cell; /. tnchogen cell; k, tormogen 

 cell; /, oenocyte; m, haemocyte adherent to basement membrane; n, dermal gland 



