566 



THE PANORPOID COMPLEX, 111., 



the second stage of evolution in Rhyacophila, but more trans- 

 versely placed. This condition is illustrated very well in the 

 Stratiomyiid genus Sargus (Text-fig. 43) and others of the 

 same family. I do not know of any Dipteron in which the 



Text-Fig. 43. 



Base of wing of Sargus sp. (Order Diptera, fam. Stratiomyiidae) , to 

 show presence of reduced cubito-median T-vein. Lettering as on 

 p. 535. 



complete archaic form of the Y-vein can be made out; though 

 I think that it may well be visible in the pupae of some of the 

 older types, which have not yet been obtained. Thus the evi- 

 dence in this Order, though containing nothing against the sup- 

 position that the evolution of the Y-vein has been along the 

 same lines as in the Triehoptera, is still not by any means as 

 complete as we could wish. 



(5) The Megaloptera. 



In this order we meet with a peculiar position. In the more 

 advanced groups, viz. the Raphidioidea and the family Sialidae 

 of the Suborder Sialoidea, the forewing shows always a more 

 or less complete fusion of Mi_4 with Ciij basally, as in the 

 third stage of evolution of the arculus in the Rhyacophilidae 

 (Text-fig. 42, d) . In the hindwing, the Y-vein is still evident, 

 though its branches are generally much shortened, and M 5 ap- 

 pears as a very short vein. This condition is shown in Text- 

 fig. 44, a, drawn from the archaic Sialid genus Stenosialis. 



Turning to the family Corydalidae, which is generally ad- 

 mitted to be the most archaic family in the Order, and from 



