618 



THE PANORPOID COMPLEX, 111., 



R 2+3 (contrast with this the line of evolution in the Nemocera) ; 

 the archaic condition of the median cell (mc) with the four 

 branches of M 1— . normally situated with regard to it; and the 

 presence of the cross-veins r-m, im and m-cu, as well as the 

 lower portion of ir, in the form of a stump-vein. The humeral 

 veinlet (hm) is also present. 



The line of evolution within the Braehycera leads to a number 



Text-Fig.t>8. 

 Forewings of a, Tabanus circumdatus Walk. (fain. Tabanidae). (x8). 

 and b, Rhyphus brevis Walk. (fam. Rhyphidae). (x 15) Letter- 

 ing- as on p. 535. Note the condition of Mi and Cui. (See also 

 Text-fig\48). 



of venational types in which a reduction is brought about hy 

 the formation of Y-veins of the type already noted in Sections 

 hi., v., vi., but in this Order affecting all the distal branches 

 of the main veins. The Y-vein is formed by fusion of two 

 veins distally, and may be brought about onlv after much altera- 



