60 



FIRST BOOK OF ZOOLOGY. 



In all these wings the pupil will observe a net-work of 

 lines, which stiffen the wing and support the delicate mem- 

 brane constituting the wing, just as the frame of a kite 

 stiffens and supports the paper that is stretched upon it. 

 These lines are called veins, or nervures. To study the vena- 



FIG. 60. AN IN- FIG. 61. AN INSECT WITH 

 BECT WITHOUT TWO WlNGS. 



WINGS. 



FIG. 62. AN INSECT WITH FOUR WINGS. 



tion of the wings, is to study the way in which these veins 

 are arranged. It would be well for the pupils to stick upon 

 a card a number of different kinds of wings, such as those 

 of the grasshoppers, beetles, flies, wasps, and label them 

 accordingly. 



58. In many insects the forward and hinder pair of wings 

 are of the same nature, as in the butterflies, moths, bees, 

 wasps, and dragon-flies. In other insects, however, the for- 

 ward-wings differ in character from the hind-wings. Thus, 

 in the grasshopper the forward pair of wings are more 

 dense in structure than the hind-wings, though the little 

 veins may be seen closely crowded together. They differ as 

 well in form. (See Fig. 64.) 



In other insects, as in the squash-bug, the front-wings 



