THE WINGS OF DIPT ERA 



353 



at the margin of the wing. The result of this coalescence is the reduction 

 of cell Ri to a small quadrilateral area; in the wing shown at c, the coal- 

 escence of veins Ri and R2+3 is complete and cell Ri is obliterated. 



2d A*Cu, 



Fig. 366. — Wing of Thereva. 



The media. — A comparatively generalized condition of media exists in 

 the wings of Rhyphiis (Fig. 357), which differs from the hypothetical primi- 

 tive type only in the fact that vein M4 has coalesced either with vein Ma 

 or with vein Cui. 



The three-branched condition of media is preserved in many families of 

 this order and is illustrated by several of the figures given later. 



In the reduction of media in this order each of the different methods 

 known has taken place. In Dixa (Fig. 365) and in the fungus gnats 

 represented in Figure 361, veins Mi and Mo have coalesced. It is probable 

 that this coalescence proceded outward. In Rhynchocephalus (Fig. 358), 

 veins Mi and Mo coalesce at the margin of the wing and the coalescence is 

 proceding inward. In the gall-gnat represented by Figure 363, only a 

 slight vestige of media remains; here the last stage of the reduction was 

 doubtless due to atrophy. And in the insects discussed in the following 



R 



h ' 



R. 



Fig. 367. — Wing of Eulonchus. 



section of this chapter media is reduced by coalescence with an adjacent vein. 



The coalescence oj veins A/3 and Cu\- — One of the most striking of the 



modifications of the wings of Diptera is the coalescence in certain forms of 



