88 



ZOOLOGY. 



up ; but the forcing of air into the tracheae quickly 

 causes them to unfold. A firm substance is now 



Fig. 59.— Leg of a Ground Beetle (X 2). 



deposited in the larger trachese, which are thus con- 

 verted into veins or ribs giving support to the wings. 

 In beetles the fore wings are quite hard and horny, 

 and serve for protecting the delicate hind-wings and 

 soft back rather than for flight; they are therefore 

 named " wing-covers " (elytra). In many insects the 

 fore wings (wasps) or the hind wings (beetles, grass- 

 hoppers) are folded when at rest. 



The abdomen only bears organs of movement in 

 caterpillars (Fig. 60) and a few other insects in the 



Fig. 60.— Silkworm Moth (Bomlyx mori). Female moth, caterpillar, pupa aud cocoon. 



young condition, and in these cases they are not 

 jointed like the true legs or " thoracic feet," but un- 

 jointed pro-legs or "abdominal feet." In the adult 



