THE FLIGHT OF INSECTS 



The subordination of the hind-wings to the fore-wings has led 

 in many cases, e.g. Bees, to a diminution in size of the former. 

 And in ordinary Two-winged Flies (Diptera) this reduction has 

 gone so far that the hind-wings have dwindled to a pair of club- 

 shaped " balancers " (kalteres) which appear to be chiefly useful as 

 sense organs, though they also play a subordinate part in flight. 



But, on the other hand, there p 



are many insects in which the 

 hind-wings are the chief agents 



Fig. 841. Wings of Insects 



A, A Dragon-Fly. B, Left fore- and hind- wings of a Moth; note frenulum projecting from base of latter. 

 C, left fore- and hind-wings of a Bee, showing row of hooks on latter. D, Two-Winged Fly; b, one of reduced 

 hind-wings. E, Male Stylops; f.w., reduced fore-wing. The figures have been drawn to various scales. 



in flight, the fore-wings having become more or less hard and 

 thick to constitute protective wing-covers. The most familiar 

 case of the kind is afforded by the Beetles (Coleoptera), although 

 it is supposed that in these insects the firm wing-covers (elytra) 

 play a passive part in flight by acting as " wind-catchers", or kites. 

 The membranous hind-wings of a Beetle, when not in use, are 

 neatly folded up under the wing-covers, and are so long that 

 they do not merely shut up like fans, but also have to be bent 

 up along a transverse crease. In some Beetles which possess a 



VOL. III. 



83 



