104 



media. The furrows are represented by dotted lines in the 

 figures. 



In the anal area (/>., that portion of the wing back of the 

 anal furrow) the three typical veins are preserved ; but they 

 coalesce to a considerable extent, both at the base and near 

 the margin of the wing. 



In the basal part of the pre-anal area [i.e.^ that portion of 

 the wing in front of the anal furrow) the stems of the princi- 

 pal veins are as follows : the costa coincides with the costal 

 margin of the wing (Fig. 6, C) ; the subcosta {Sc) is well pre- 

 served and is forked ; back of the subcosta is a strong stem 

 formed by the coalescence of the other three veins ; the 

 cubitus (Cti) 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 we have marked 

 the free portion of the media 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 could not have been solved by a 

 study of Hymenoptera alone. But a knowledge of the meth- 

 ods of specialization of the wings of Diptera gives a key to an 

 understanding of the wings of Hymenoptera. 



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 order named : a Bombyliid, 

 a Scenopinid, and an Empidid. Now study the figure of a 

 wing of Rhyphus (Fig. 2, p. 87) and note that while in Rhyphus 

 veins Cu^ and ist A retain their primitive position, in the 

 three wings named above these two veins exhibit varying de- 

 grees 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 vein : and this coalescence has 



