28 



The Form of Insects 



The firm fore-wings of Cockroaches serve as covers 

 beneath which the delicate hind-wings can be folded 

 after the manner of a fan, and protected when not in 

 use (fig. 22). In this respect the cockroach is more 

 highly specialised than many other insects, which 

 have all four wings of thin texture. In Dragonflies 

 the two pairs of wings are closely alike in size and 

 form. Often the front-wings are both larger and 

 broader than the hind-wings, as in the Mayflies, Bees, 

 Wasps, and their small relations, the extreme stage 



Fig. 22.— Cheese-fly {Piophiia casei). d. Male ; e. female with wings folded. 

 Magnified 8 times. From Howard, Bull. 4 (n.s.) Div. £nt. U.S. Dept. Agr. 



being reached in the Flies (fig. 22), whose hind-wings 

 are reduced to small stalked knobs. Or the fore-wings 

 are longer than the hind-wings, but also narrower, 

 as in Stoneflies, Caddis-flies, and many Moths. In 

 this latter case there is a tendency for the fore-wings 

 to become of firmer texture than the hind-wings, and 

 for the latter to be folded beneath the former when 

 at rest. Thus the marked distinction between the 

 two pairs which we notice in the Cockroach is reached, 



