PHYLUM ARTHROPODA 



245 



vures. In most of the butterflies and moths (Fig. 143) the 

 wings are opaque, owing to their being covered with numer- 

 ous overlapping microscopic scales to which the various 

 colours of the wing are due. In the beetles (Fig. 144), 

 locusts, and others, on the other hand, the posterior wings 

 alone are membranous, the anterior pair being converted 

 into hard and tough cases — the elytra — which, when 

 folded up, cover over and protect the delicate posterior 

 wings. In the bugs and their allies, the anterior wings are 



Fig. 144. — d, Carpet beetle (Anthrenus scrophularise) with larvart, b, and pupa, c. 

 (After Riley, from Bulletin of Division of Entomology, United States Depart- 

 ment of Agriculture.) 



thick and opaque at the bases only. In the house-flies, 

 gnats (Fig. 145), and their allies (order Diptera), the ante- 

 rior wings alone are developed, the posterior being rep- 

 resented by vestiges, the halteres or balancers. In the 

 bee-parasites the posterior pair of wings are alone devel- 

 oped, the anterior pair being vestigial. In some insects 

 (springtails, lice, fleas) wings are entirely absent in all 

 stages. In others again, as certain moths, they are present 

 in one sex — usually the male — and absent in the other. 



