14 TIIK LIFE-SToKY OF INSECTS [CH. 



wing (fig. 5). After the last moult the wings are 

 exposed, articulated to the segments that bear them, 

 and capable of motion. Having been formed beneath 

 the cuticle of the wing-rudiments of the penultimate 

 instar, the wings are necessarily abbreviated and 

 crumpled. But during the process of hardening 

 of the cuticle, they rapidly increase in size, blood 

 and air being forced through the nervures, so that 

 the whigs attaining their full expanse and firmness, 

 become suited for the function of flight. 



The changes through which these insects pass are 

 therefore largely connected with the development of 

 the wings. It is noteworthy that in an immature 

 cockroach the entire dorsal cuticle is hard and firm. 

 In the adult, however, while the cuticle of the pro- 

 thorax remains firm, that of the two hinder thoracic 

 and of all the abdominal segments is somewhat thin 

 and delicate on the dorsal aspect. It needs not now 

 to be resistant, because it is covered by the two firm 

 fore wings, which shield and protect it, except when 

 the insect is flying. There are, indeed, slight changes 

 in other structures not directly connected with the 

 wings. In a young grasshopper, for example, the 

 feelers are relatively stouter than in the adult, and 

 the prothorax does not show the specifically dis- 

 tinctive shape with its definite keels and furrows. 

 Changes in the secondary sexual characters may also 

 be noticed. For instance, in an immature cockroach 



