350 



THE WINGS OF DIPT ERA 



place here, the third branch of media is vein M3 and the vein behind it is 

 vein CU1+M4. This, as shown in the preceding chapter, is probably the 

 method of reduction of media that has taken place in the suborder Frenatae 

 of the Lepidoptera; bvit there the coalescence of the two \'eins preceded 

 outward. 



The figure of a wing of Protoplasa (Fig. 360) is labeled in accordance 

 with this theory. But until more evidence as to the fate of vein M4 is 



obtained it seems best to omit 

 ^R.+i any reference to this vein in 

 the designation of the veins of 

 the Diptera. 



Specializations within the 

 order. — While a partial reduc- 

 tion of the anal area and the 

 loss of vein M4 as a distinct 

 vein are characteristic of recent 

 Diptera as a whole, the greater 

 number of specializations ex- 

 hibited by the wings of Dip- 

 tera have arisen within the 

 order and have been earned 

 to widely different degrees in 

 different members of the order. 

 The most practicable way of 

 discussing these specializations 

 is to treat of the modifications 

 of each of the principal veins 

 separately. 

 ^"' "' The costa. — The costa is 



Fig. 361.— Wings of fungus gnats. marginal. I have no data to 



give regarding modifications of its extent. 



The subcosta. — The primitive, two-branched condition of the subcosta 

 is preserved in a very few forms; one of these is Protoplasa (Fig. 360). In 

 most members of the order it is not branched. In some cases the tip of the 

 simple subcosta ends in the margin of the wing, indicating that vein Sc-z 

 is lost; In other cases the tip coalesces with vein Ri, indicating that vein 

 Sci is lost. Frequently the subcosta is greatly shortened. 



Three widely different conditions of the stibcosta exist in the three 

 wings of fungus-gnats represented in Figure 361; in the first it is greatly 

 shortened, in the second it is tw^o-branched , and in the third it coalesces with 

 radius for the greater part of its length. 



The radhis. — In a few genera of flies the radius retains its primitive, 

 five-branched condition; the genus Protoplasa of the Tipulida? has already 



