INSECTS 



insects; but it is evident that the majority of insects 

 have found it more advantageous to have the fore and 

 hind wings different in one way or another. 



In the grasshoppers, it was observed (Fig. 63), the hind 

 wings are expanded into broad membranous fans, while 

 the fore wings are slenderer and of a leathery texture. 

 The same is true of the roaches (Fig. 53), the katydids 

 (Fig. [68 B), and the crickets, except in special cases where 

 the fore wings are enlarged in the male to form musical 

 organs (Fig. 39). In all these insects the hind wings are 

 the principal organs of flight. When not in use they are 

 folded over the body beneath the fore wings, which latter 

 serve then as protective coverings for the more delicate 

 hind wings. In the beetles (Figs. 137, 168 C) the hind 

 wings are much larger than the fore wings, and, as with 

 the grasshoppers and their kind, thev take the chief part 

 in the function of flight. The beetles, however, have 

 carried the idea of converting the fore wings into pro- 

 tective shields for the hind wings a little farther than have 

 the grasshoppers; with them the fore wings are usually 

 hard, shell-like flaps that tit together in a straight line over 

 the back (Fig. 137 A), forming a case that completely 

 conceals, ordinarily, the membranous hind wings folded 

 beneath them. Neither the grasshoppers nor the beetles 

 are swift or particularlv efficient fivers, but thev appear to 

 demonstrate that the ordinarv insect mechanism of flight 

 is more effective with one pair of wings than with two. 



The butterflies and the moths use both pairs of wings 

 in flight; but with these insects, it is to lie noted, the front 

 wings are always the larger (Fig. 168 D). The butterflies, 

 with tour broad wings, flv well in their way and are ca- 

 pable of long-sustained flight, though they are compara- 

 tively slow goers. Some of the moths do much better 

 in the matter of speed, but it is found that the faster flying 

 species have the fore wings highly developed at the ex- 

 pense of the hind wings; and that the two wings on each 

 side, furthermore, are yoked together in such a manner as 



[318] 



