Wings 29 



and by a further development along the same lines, 

 the fore-wings become so hard and horny that they 

 can hardly be considered as "wings" at all, their 

 function being simply to act as protecting sheaths for 

 the hind-wings, which alone are used for flight, as in 

 Beetles (fig. 69) and Earwigs. The wings of many 

 insects are fringed or covered with hairs or bristles ; 

 those of Butterflies and Moths, Gnats, and other 

 insects are clothed wholly or in part with flattened 

 scales (fig. 9 g. h.). 



In the female Cockroach the fore-wings are small, 

 movable plates, reaching back only to the middle of 

 the third segment of the fore-body ; the hind- wings 

 are represented only by a network on each outer 

 corner of the metanotum. Organs thus reduced 

 are said to be vestigial, and this is the condition 

 of the wings in many female insects whose males 

 have them well developed. In the American and 

 German (fig. 94) cockroaches, not distant relations of 

 our common kind, the wings of both sexes are, how- 

 ever, nearly similar. The presence of wings in the 

 female of the common cockroach, in a reduced or 

 vestigial condition, suggests that its ancestors had 

 females winged like the males, a view confirmed by 

 the presence of well-developed wings in the females 

 of the allied kinds. And the vast majority of wing- 

 less insects are believed to be the descendants of 

 winged ancestors. In many aquatic insects a tendency 

 towards loss of wings can be observed. Certain water- 

 bugs, for example, are habitually wingless, but the 

 occasional presence of a winged specimen shows that 

 the whole race has not yet lost the organs of flight. 

 The small and humble insects known as Springtails 

 and Bristletails are all wingless ; as none of them 

 have even traces of wings, and they are not nearly 

 related to other insects, it is believed that the 



