240 THE WINGS OF ODONATA 



The hind wing of Gomphus descriptus (Plate IV) may be taken as an 

 illustration of a wing which lacks an anal loop. In this wing veins Ai, A2, 

 and A3 extend in a nearly parallel direction to the inner margin of the wing. 



In Cordulegaster sayi (Fig. 230) vein Ai coalesces with vein Cu2 for a 

 short distance and then extends obliquely towards the anal angle until it 

 is met by a branch of vein A2, in this way there is enclosed a polygonal 

 space between veins Ai and A2 and is formed what is termed the anal loop 

 (Fig. 230, al). 



The supplemental anal loop. — In some genera of the Aeschnin^ there 

 exists a second anal loop, which is termed the supplemental anal loop this 

 is shown in the hind wing of Anax Junius (Fig. 236, al'). 



Fig. 240. — Wings of Orthemis ferriiginea. 



The cuhito-anal or foot-shaped loop. — -In the Libellulids vein Ai is 

 greatly shortened; it ends at the point where it joins vein Cu2 at the 

 posterior corner of the triangle (Fig. 240). The result of this is that the 

 loop formed in the anal area is developed between veins A2 and Cu2; 

 for this reason it is termed the cuhito-anal loop (Fig. 240, cual). On account 

 of its peculiar form it was termed by Needham the foot-shaped loop; and for 

 the same reason Tillyard designates it the Italian loop, as it resembles in 

 outline a map of Italy. 



The cubital supplement. — The cubito-anal loop is divided longitudinally 

 by a midrib-like vein, which is not formed about a trachea; this vein is 

 termed by Tillyard ('14) the cubital supplement (Fig. 240, cuspl). 



The quadrangle of the Zygoptera. — In the suborder Zygoptera, or damsel- 

 flies, the cubitus and its first branch, vein Cu], extend in a comparatively 

 direct course from the base of the wing outward (Plate IV, Fig. 2); the 



