30 INSECT A. 



the front or costal margin, the outer or apical, and 

 the inner or anal. The important veins divide the 

 wing into the three areas, costal, median, and anal. 

 When the wings are expanded as in the act of flying 

 (PI. I., Fig. i), the forward part is rigid, owing to the 

 larger veins which radiate from the base, while the 

 posterior portion is flexible. The wings are attached 

 to the tergal portions of their respective rings, which 

 are loosely connected with the lateral parts. The 

 movements of each tergum, which are accomplished 

 in the living locust by strong internal muscles, may 

 be imitated by gently pressing the tergum downward, 

 when the wings will be seen to rise. It is instructive 

 to observe the correspondence existing between the 

 size of the wings, and that of the rings upon which 

 they are borne. In the locust and most Orthoptera, 

 whose posterior wings do the larger part of the work 

 of flying, the metathorax is larger than the meso- 

 thorax ; but in other insects, like the butterfly and fly, 

 which use their first pair of wings more than the 

 second pair, the reverse will be seen to occur. The 

 greater amount of work done by the muscles within 

 these rings in moving the wings causes their own en- 

 largement, and the segment necessarily grows more 

 capacious to make room for the accommodation of 

 the muscles. 



The wings are membranous expansions quite dif- 

 ferent in aspect from the body wall, but are con- 

 sidered to be folds of the skin which have grown out 

 from the tergal portions of their respective rings. 

 They are mere pads in the young, and their veins are 

 hollow, some of which contain tracheae. This has led 



