THE WIISCS OF HYMENOPTERA 365 



area ; the cubitus (Fig. 382, Cu) soon separates from this stem, extending in 

 a curve towards the anal furrow; while the radius and the media coalesce 

 for about half their length. In order to make these veins more distinct in 

 the figure the free portion of the media is marked with cross lines ; see also 

 Plate X. 



When we pass from a consideration of the main stems of the veins to a 

 study of the branches, we meet a much more complicated problem, a 

 problem that could not have been solved by a study of Hymenoptera alone. 

 But a knowledge of the methods of specialization of the wings of Diptera 

 gives, as already stated, a key to an understanding of the wings of Hymen- 

 optera. 



If the reader will examine the series of figures illustrating the coalescence 

 of veins Cu^ and 2d A in the Diptera (page 3 5 5) , he will find it easy to under- 

 stand what has taken place in the Hymenoptera. In the Hymenoptera, 

 however, both branches of the cubitus coalesce with the first anal vein ; and 



li^ A Cu. Cu.' 

 Fig. 384. — Wing of Pantarbes. 



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. 



It should be noted that vein Cu2 is comparatively rarely preserved in 

 this order. Dr. MacGillivray, in his very extended study of the wings of the 

 Tenthredinoidea, (MacGillivray '06, p. 552), notes its presence in represen- 

 tatives of several genera of the Lydidje ; but in most of the Tenthredinoidea 

 all traces of it are lacking. 



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

 Ml (Fig. 382) extends longitudinally near the center of the distal part of the 

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

 a course similar to the course of this vein in the dipterous gentis Pantarbes 

 (Fig. 384). Vein M3 extends across the anal furrow near the margin of the 

 wing and coalesces with the first anal vein. It is evident that the forces 

 that are causing the branches of the cubitus to migrate along the first anal 

 vein towards the base of the wing are exerting a similar influence on this 

 vein. It is also evident that veins M4 and Cui coalesce at the tip, and that 

 the migration of the united tips of these veins (marked Cui in the figure) 



