94 COKXECTICUT GEOL. AND NAT. HIST. SURVEY [Bllll. 



Bombyliidae, etc.) it is ecasy to recognize the genital forceps as such, 

 although in the Cyclorrhapha structures homologous with the genital 

 forceps have not been definitely identified. 



The Asilidae are of particular interest, since the eighth and ninth 

 segments (with the proctiger) become temporarily inverted in such 

 asTlids as DasyUis and Laphria, and structures which appear to repre- 

 sent the segments of the genital forceps, labelled cxi and st, are well 

 developed in such asilids as the one shown in Fig. 10, N. Certain of 

 the appendages of the ninth tergite, 'dt, of the asilid shown in Fig. 

 10, N, may represent the surstyli, ss, of such primitive Nematocera as 

 the one shown in Fig. 10, K, and these appendages become of increas- 

 ing importance in the types ancestral to the Cyclorrhapha, in which 

 group i\\Q surstyli are well developed. 



The Dolichopodidae are among the most important of the orthor- 

 rhaphous Brachycera which approach the lines of descent of the 

 Cyclorrhapha, and the abdominal structures of the Dolichopodidae. 

 like those of other regions of the body in these interesting Diptera, 

 present some extremely interesting modifications. Thus, in the dol- 

 ichopodid, Scellns venustiis^ shown in Fig. 10, M, a pair of delicate 

 ribbon-like spatulate processes attached in front of the sixth sternite, 

 extends upward, one on each side of the sixth tergite, from which 

 they project backward as delicate processes bearing long mesal setae 

 at their tips. The function of these processes has not been de- 

 finitely determined, although they are evidently secondary sexual 

 characters of the male. 



Another interesting modification is exhibited b}^ the dolichopodid, 

 DoUchopus julvi'pes^ shown in Fig. 10, D, which has a membranous, 

 ventral, bilobed sac, bearing the label en in Fig. 10, D. This struc- 

 ture appears to be of the nature of an eversible "scent sac", which is 

 protruded at the time of mating, although its function has not been 

 definitely determined. Eversible sacs also occur in the abdominal 

 region of the males of some Empidae and a few other Diptera. 



The cerci are much better developed in the males than in the 

 fenudes in the Dolichopodidae, and in the male dolichopodid shown in 

 Fig. 10, D, the cerci, ce, are broad, flat, fan-like, fringed plates, while 

 in the dolichopodid, Limiculus hydrophilus, figured by Snodgrass 

 (1904), structures which appear to be homologous with the cerci (or 

 surstyli?) project forward as long slender processes extending to the 

 ventral region of the thorax in this insect. 



In some Dolichopodidae in which a torsion of the postabdomen 

 occurs, the cavity of the body opens into the eighth segment through 

 an aperture situated on the left side, instead of being located ante- 

 riorly as is usually the case; and the terminal abdominal structures of 

 the Dolichopodidae are of great interest for the study of the modi- 

 fications occurring in the Cyclorrhapha, as will be discussed later. 



In addition to. the Dolichopodidae, Asilidae, etc., which in some 

 cases exhibit a marked torsion in the segments of the postabdomen 

 (most male Diptera are apparently capable of twisting the parts 

 about temporarily during the mating process), other Brachycera such 



