410 THE WINGS OF INSECTS 



vein; and this coalescence has proceeded so far that both branches cross 

 the anal furrow and end in the anal vein remote from the margin of the 

 wing. (See Fig. 425). 



It should be noted that vein Cu2 is rarely preserved in this order, even 

 in the more generalized forms. In Macroxyela (Fig. 424) the position of 

 the fork of the cubitus is indicated by a bend in this vein. 



If the branches of the media be now examined, it will be seen that vein 

 Ml (Fig. 425) extends longitudinally near the centre of the distal part of the 

 wing, its primitive course being modified slightly if at all. Vein M2 follows 

 a course similar to the course of this vein in the Bombyliid; so also does the 

 medial cross-vein (Fig. 425, m). A comparison of the position of cells Mi, 

 ist Mo, and 2d Mo in the Bombyliid and in the typical hymenopterous wing 

 (Fig. 426) is very instructive. 



Returning to Pampkilius (Fig. 425), we see that vein M3 coalesces with 

 the first anal vein, crossing the anal furrow near the margin of the wing. It 

 is evident that the forces that are causing the branches of the cubitus to 

 migrate along the first anal vein and towards the base of the wing are 

 exerting a similar influence on this vein. It is also evident that vein M4 

 and Cui coalesce at the tip, and that the migration of the united tips of these 

 veins (marked Cui in the figure) towards the base of the wing has so modi- 

 fied the course of that part of vein M4 which is still free that this part of 

 this vein extends towards the base of the wing. This change is very similar 

 to the change in the course of vein Cuo in the Empidid. 



A curious result of this change in the direction of the course of vein M4 

 is that the cell M4 has been closed and pressed back to the centre of the 

 wing (Fig. 426, M4), and now lies in front of the free portion of the vein M4 

 instead of behind it. 



Let us now consider the courses of the branches of the radius. Here 

 again we can gain help from a study of dipterous wings. Observe in the 

 Bombyliid (Pantarbes) the coalescence of the tips of veins R5 and Mi. In 

 the Hymenoptera a similar coalescence of veins R5 and Mi has occurred; 

 but it has proceeded much farther, so that the free portion of vein Rj in 

 Pampkilius (Fig. 425, R5) is remote from the end of the wing and has the 

 appearance of a cross-vein. 



In the Hymenoptera vein R5 has been followed in its migration along 

 vein Ml by vein R4, which has now reached a stage in Pamphilins that is 

 quite similar to that reached by vein R5 in Pajitarbes. But like vein R5 it 

 has the appearance of a cross- vein. 



From this it will be seen that the vein marked Mi in Figure 425 is really 

 compound, as it includes the tips of veins R5 and Ri. 



In Pamphilins vein Ri is curved away from the costal margin of the 

 wing to make room for a stigma (Fig. 426, S), and vein R3 ends in the costal 

 margin a short distance before the apex of the wing (Fig. 425). Vein R2 



