MOSQUITOES AND FLIES 



are provided with sets of highly developed wing muscles 

 which are much more effective than those of other insects. 

 From these examples, therefore, we can not well judge 

 of the mechanical efficiency of two pairs of equal wings 

 moved by the equipment of muscles possessed by most 



Fig. i 68. Evolution of the wings of insects 

 A, wings of a termite, approximately the same in size and shape. B, wings 

 of a katydid, the hind wings are the principal organs of flight. C, wings of 

 a beetle, the fore wings changed to protective shells, elytra (El), covering the 

 hind wings. D, wings of a hawk moth, united by the spine (/), which is 

 held in a hook on under surface of fore wing. E, wings of the honeybee, 

 held together by hooks (h) on edge of hind wing. F, wing of a blowfly, 

 and the rudimentary hind wing, or halter (HI) 



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