ODONATA 



317 



The head is large, broad, often semi-globose, and concave behind. 

 The wings are very strong. An important factor in the strengthening 



Fig. 362. — Wings of naiads of Gomphiis descripttis, early stages. (From Comstock 

 and Needham.) 



of the wings of these insects is the development of a series of cor- 

 rugations, which has resulted in certain veins becoming convex and 

 others concave ; this has progressed so far that there is a very perfect 

 alternation of convex and concave veins. 



The habits of dragon-flies have been carefully studied by Professor 

 Needham ('18), who writes as follows: 



"Among the dragon-flies are many superb flyers. The speed on the wing of 

 Trdmea and Anax equals, and their agility exceeds, that of swallows. They all 

 capture their prey in flight; and are dependent on their wings for getting a living. 

 But the habit of flight is very different in different groups. Only a few of the 



Fig. 363. — Tracheation of the wings of a grown naiad of Gomphus descriptus. 

 (After Needham.) 



