FLYING ANIMALS. 21 



fled into the well-known horn-like wing-covers, or 

 elytra, beneath which the membranous second pair are 

 neatly folded during such times as the creatures are 

 not engaged in flight. In some kinds, such as the 

 Stag-Beetle and the Water-Beetles, these wing-cases 

 are long, and extend backwards to the hinder extre- 

 mity of the body ; but in others, like the well-known 

 " Devil's Coach-Horse," they are extremely short. The 

 modification of the front wings into wing-covers clearly 

 indicates that Beetles are a highly specialised group ; 

 the extreme development of this specialisation occur- 

 ring in certain species like the Oil Beetle, where the 

 second pair of wings have also become rudimentary, so 

 as to render their owner incapable of flight. In some 

 degree a confirmation of this specialisation is afforded 

 by the circumstance that Beetles are not known in the 

 fossil condition so far down in the geological scale as 

 are some of the more generalised groups of insects. 



In the Bees, Wasps, Ants, and other members of the 

 second order Hymenoptera, both pairs of wings are 

 membranous and adapted for flight; the front pair 

 being, however, considerably the larger of the two. In 

 the Caddis Flies and other Neuroptera, both pairs of 

 wings are likewise fully developed and membranous in 

 structure, although differing in the mode of arrange- 

 ment of their veins. Moreover, the hinder pair are 

 frequently nearly as large as the front pair a circum- 

 stance which seems to indicate that the whole group is 

 a more generalised one. The development of the well- 

 known minute scales on both pairs of wings in the 



