252 



THE WINGS OF PLECOPTERA 



Fig. 250. — Wing of Capnia. 



The Pteronarcidae. — Of the three known genera representing this 

 family, it is evident that so far as the venation of the wings is concerned the 

 genus Pteronarcella is the most generahzed.* 



In Pteronarcella hadia (Fig. 251) the plecopterous type of wing- venation 

 is very shghtly modified. Media is clearly two-branched in both fore and 

 hind wings. The first branch of the radial sector, vein R2+3, bears a few 

 branches; but here, as elsewhere in the order, a comparison of allied species, 

 or even of different individuals of the same species shows that these branches 



can not be considered pri- 



mitive. 



The data given above 

 show that in tracing the 

 methods of specialization 

 of the wing-veins in the 

 Plecoptera we should start 

 with a form in which the 

 radial sector and the 

 media are each only two- 

 branched. I have selected 

 Nenionra,\he better known 

 representative of the more 

 generalized suborder, as 

 the form with which to 

 make comparisons. 

 The tracheation of the wings of a nymph of Nemoura was figured by 

 Comstock and Needham (Fig. 252). This represents very closely the 

 hypothetical primitive type of tracheation except that the trachea of the 

 radial sector and of media in both fore and hind wings are only two- 





Wings of Pteronarcella hadia. 



*I have seen neither specimens nor figures of Diamphipnoa, which occurs in Chile. 

 But as this is said to resemble Pleronarcys in having cross-veins in cell R of the fore 

 wings, I feel warranted in making the above statement. 



