170 



ANIMAL LOCOMOTION. 



to fly from the hand, it extends its front legs and flexes 

 the back ones, and tilts its head and thorax upwards, so 

 as exactly to resemble a horse in the act of rising from the 

 ground. This preliminary over, whirr go its wings with im- 

 mense velocity, and in an almost horizontal direction, the 

 body being inclined more or less vertically. The insect rises 

 very slowly, and often requires to make several attempts 

 before it succeeds in launching itself into the air. I could 

 never detect any pressure communicated to the hand when 

 the insect was leaving it, from which I infer that it does not 

 leap into the air. The bees, I am disposed to believe, also 

 rise without anything in the form of a leap or spring. I 

 have often watched them leaving the petals of flowers, and 

 they always appeared to me to elevate themselves by the steady 

 play of their wings, which was the more necessary, as the sur- 

 face from which they rose was in m^any cases a yielding surface. 



The Wings of Insects, Bats, and Birds. 



Elytra or Wing-cases, Membranous Wings — their shape and 

 uses. — The wings of insects consist either of one or two pairs. 

 When two pairs are present, they are divided into an ante- 

 rior or upper pair, and a posterior or under pair. In some 

 instances the anterior pair are greatl}^ modified, and present 

 a corneous condition. When so modified, they cover the 

 under wings when the insect is reposing, and have from 

 this circumstance been named elytra, from the Greek ekvrpov, 

 a sheath. The anterior wings are dense, rigid, and opaque 

 in the beetles (fig. 89, r) ; solid in one part and membran- 

 aceous in another in the water-bugs (fig. 90, r) ; more or less 

 membranous throughout in the grasshoppers ; and completely 

 membranous in the dragon-flies (fig. 91, (3 6, p. 172). The 

 superior or upper wings are inclined at a certain angle when 

 extended, and are indirectly connected with flight in the 

 beetles, water-bugs, and grasshoppers. They are actively 

 engaged in this function in the dragon-flies and butterflies. 

 The elytra or anterior wings are frequently employed as sus- 

 tainers or gliders in flight,^ the posterior wings acting more 



1 That the olytra take part in flight is proved by this, that when they 

 are removed, flight is in many cases destroyed. 



