318 



AN INTRODUCTION TO ENTOMOLOGY 



strongest forms roam the upper air at will. There is a host of beautiful species, the 

 skimmers or Libellulidce, that hover over ponds in horizontal flight, the larger 

 species on tireless wings, keeping to the higher levels. The stronger flying ^schni- 

 dae course along streams on more or less regular beats; but the Gomphines are 

 less constantly on the wing, flying usually in short sallies, from one resting place 

 to another, and alighting oftener on stones or other flat surfaces than on vertical 

 stems." 



The characters presented by the venation of the wings of the 

 Odonata are much used in the classification of these insects. In 

 general the veins and areas of the wings are designated as in the 

 accounts of the wings of other orders of insects ; but there are certain 

 features in the wings of these insects that are peculiar to them. 



The most distinctive feature of the wings of the Odonata is the 

 fact that in the course of their development one or more branches, 

 usually two, of the medial trachea invade the area of the radial sector. 



Fig. 364. — Wings of Gomphus descriptus. In the front wing, cells or areas are 

 labeled; in the hind wing, veins. 



This results in vein Rg occupying a position behind one or more, 

 usually two, of the branches of media. Figure 362 represents the 

 tracheation of the wings of two naiads of Gomphus descriptus; the 

 wing shown at A is of a very young naiad ; that at B is of a somewhat 

 older one. In the wing shown at A, the branches of trachea M are in 

 their typical position; in the wing shown at B, trachea Mi is in front 

 of trachea Rs. Figure 363 represents the tracheation of a full-grown 

 naiad of the same species. In this stage of the development of the 

 wings, both tracheas Mi and Mo are in front of trachea Rs; and it is 

 in this position that the veins of the adult wing are developed (Fig. 

 364)- 



