THE WINGS OF INSECTS 



409 



Stem formed by the coalescence of the other three veins; the cubitus (Cu) 

 soon separates from the 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. 



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

 branches, we meet a much more complicated problem, a problem which 



Fig. 425. — The veins of a typical hymenopterous wing; a fore 

 wing of Pamphilius with vein R2 added. 



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 a 

 key to an understanding of the wings of H^Tnenoptera. 



We will study first the branches of the cubitus. Spread out before you 

 your drawings of the wings of the following insects, and arrange them in the 



Fig. 426. 



-The cells of a typical hymenopterous wing; a fore wing 

 of Pamphilius with vein R2 added. 



order named: a Bomb}-liid, a Scenopinid, and an Empidid. Now study 

 the figure of a wing of Rhyphus (Fig. 410) and note that while in Rhyphns 

 veins Cu2 and 2d A retain their primitive position, in the three wings named 

 above these two veins exhibit varying degrees of coalescence. 



A similar method of specialization has taken place in the Hymenoptera, 

 but in this order both branches of the cubitus coalesce with the first anal 



