CHAPTER XI 

 THE V/INGS OF THE ODONATA 



Fig. 225. — A dragon-fly. 



(a) THE MORE GENERAL FEATURES OF THE WINGS OF THE ODONATA 



In the Odonata the wings are long and narrow and are finely netted with 

 cross-veins; the hind wings are as large as or larger than the fore wings; 



and each wing has on its cos- 

 tal margin a joint-like struc- 

 ture, the nodus. 



In the dragon-flies, sub- 

 order Anisoptera, the wings 

 are held extended at right 

 angles to the length of the 

 body when the insect is at 

 rest (Fig. 225). 

 In this suborder the wings 

 are exceedingly efficient 

 organs of flight; few if any 

 insects exceeding the dragon-flies in rapidity of flight. The damsel-flies, 

 suborder Zygoptera, are furnished with more delicate wings, which, as 

 a rule, are folded together above the abdomen 

 when not in use (Fig. 226), although in the Lestinae 

 they are partly spread. 



The most distinctive feature of the wings of the 

 Odonata is the fact that in the course of their onto- 

 genetic development one or more, usually two, of 

 the branches of the medial trachea invade the 

 area of the radial sector. This results in vein Rg 

 occupying a position behind one or more, usually 

 two, of the branches of media. This remarkable 

 phenomenon is discussed more at length a little 

 later. There are reasons to believe that a similar 

 invading of the area of the radial sector by media 

 takes place in the Ephemerida. With this excep- 

 tion it is distinctively characteristic of the Odonata. 

 The growth of our knowledge of the homologies 

 of the wing-veins within the order Odonata has been 

 a gradual one and is the result of the contributions of many authors; chief 

 among whom are Hagen, Walsh, and Baron de Selys-Longchamps. But 

 a complete understanding of the correspondence in detail of the wing- 

 veins of the Odonata with those of the wings of insects of other orders 



(224) 



Fig. 22b. — A (iamsel-fly. 



