THE WINGS OF PLECOPTERA 257 



Correlated with the development of one or more accessory veins on 

 vein Cui there is a tendency of this vein to curve forward towards media, 

 which frequently results in an anastomosis of these two veins. In the fore 

 wing of Isogenus (Fig. 245) this extension forward of vein Cui is marked; 

 but the cross-vein m-cu still persists. In the hind wing of this species, the 

 cross- vein m-cu has been obliterated by the anastomosis of veins M3+4 

 and Cui. The result of this anastomosis is to produce the appearance of 

 media being three-branched; but what appears to be the third branch of 

 media is vein Cui. 



The first anal vein. — Occasionally, as in some species of Pteronarcys, the 

 first anal vein is forked at the tip ; but, as a rule this vein is unbranched in 

 both fore and hind wings. 



The second and third anal veins. — The anal area of the fore wings is 

 rarely expanded, the second and third anal veins remaining unbranched in 

 most genera; but in a few cases, as in Pteronarcys (Fig. 254), these veins 

 are branched. 



In the hind wings, the anal area is expanded in many genera; and 

 correlated with this expansion, there is a branching of both the second and 

 third anal veins; this is shown in Isogenus (Fig. 245) and in Pteronarcys 

 (Fig. 254). 



The most remarkable expansion of the anal area of the hind wings that 

 I have observed in this order is that of Eusthenia spectabilis (Fig. 246). 

 There is here a certain resemblance to the hind wing of an orthopterous 

 insect ; for in several places there are what appears to be the beginnings of 

 the development of intercalary veins. 



