THE WINGS OF TRICIIOPTERA 317 



In the hind wings the cubital and first anal trachea? coalesce for a short 

 distance, but the two soon separate; they extend parallel in the coalesced 

 vein until the point is reached where the two veins separate and then each 

 follows its vein. The base of the free part of vein Cu makes a sharp cuxxq 

 towards the base of media but does not quite reach it, the two veins are 

 connected by a short posterior arculus in which there is no trachea. Directly 

 opposite the point of separation of the cubitus and the first anal veins, the 

 first anal vein is joined by the second anal vein, the trachea of which is 

 perfectly distinct. The tracheae of the two veins continue parallel until 

 the two veins separate and then the second anal trachea follows its vein. 



(c) THE ZOOLOGICAL POSITION OF THE MICROPTERYGID.5 



If the wings of Mnemonica, one of the more generalized of the Alicro- 

 pterygidae (Fig. 324), be compared with those Rhyacophila, one of the more 

 generalized of the Phryganeina (Fig. 320), it will be seen that they agree 

 in the more essential features of their venation ; the more striking character- 

 istics of the one are presented by the other. These characteristic features 

 are the following. In the fore wings, the coalescence of veins Cu and ist A 

 at the base of the wing ; the Z-shaped course of vein Cu ; the formation of a 

 serial vein consisting of the base of media, the posterior arculus, and the 

 longitudinal part of ^•ein Cu ; the coalescence of the tips of the second anal 

 vein arid of two of the branches of the third anal vein ; and the cross-vein 

 between the first and second anal veins. In the hind wings, the coalescence 

 of veins Cu and ist A at the base of the wing; the Z-shaped course of the 

 cubitus; the anastomosis of the first and second anal veins; the longitu- 

 dinal direction of the cross-vein connecting the second anal vein and the 

 first branch of the third anal vein; and the form of the branching of the 

 third anal vein. In addition to these common venational features the 

 fibulse of the two insects are identical in structure. 



The possession of this remarkable series of common features of their 

 wings by these representatives of the Phryganeina and the Micropterygina, 

 and which is found in no insect not belonging to one of these two groups, 

 can be explained only by assuming that it indicates a community of descent 

 of the two groups. This conclusion is confirmed by the results of Dr. T. A. 

 Chapman's studies of pupae.* 



For these reasons, the Micropterygina must be regarded as more closely 

 allied to the Phryganeina than they are to any other group of insects; that 

 is, they are obviously trichopterous insects. 



It is also obvious that the Phryganeina and the Micropterygina represent 

 two quite distinct lines of descent from the common stem of the order and 

 should be regarded as distinct suborders. 



*Trajis. Ent. Soc. London, 1896, p. 569. 



