10 Transactions • of the Society. 



the families of the Braehycera, but is now seen to he a Nemato- 

 cerous character, and affords valuable evidence of affinity. 



In all the Stratiomyidse that I have examined, the mandibles 



are fused in the median line of the mentum, and often send out 

 lateral processes at the posterior end. Michrochrysa polita L., and 

 Chloromyia formosa Scop., have plates at the bases of the tracheae 

 similar to those referred to above (plate II. figs. 25, 26). 



The tropin in the Conopodse are of a highly specialised type, 

 and fitted for flower feeding. They are mostly analogous in 

 structure to Prosena in the Muscidre ; that is to say, the mentum 

 lias displaced all the membranous parts of the labium, and has 

 developed into a long styliform plate with the sides bent upwards, 

 and fused with the mandibles at the upper edges. Of this type 

 are Conops quadrifasciata Deg., C. jiavipcs L., and Physocephala 

 rvjipes F. 



Zodioii cinereum F. has the palpi more developed, and the 

 paraglossse are lengthened, and geniculated at the base ; Myopa 

 buccata L. has the palpi even more developed than in Z. cinereum, 

 and the paraglossre bearing well-marked tracheie. These last two 

 species have analogies in the Museidae in Siphona, and the tropin 

 of the Conopodse present, when compared with Prosena and 

 Siphona, excellent examples of parallel development. The man- 

 dibles in this family are very obvious on the dorsal side of the 

 labium, and the maxillary palpi, found in interesting stages of 

 degeneration, show the relationship to the Syrpkidse. 



Group 4. — The presence of the pharyngeal pump in the heads 

 of many Dolichopodidse is one more peculiarity in this family, 

 already remarkable for its numerous peculiarities ; it is also a 

 character that helps the solution of the problem as to their 

 phylogeny (plate II. fig. 31). 



The pump is connected with the base of the hypopharynx and 

 approximates to the mechanism found in the Empkke, but differs 

 in detail. The piston working in the cavity is a plate with the 

 sides bent to the shape of a bulb, connected with the pharynx at 

 its posterior end ; there are also openings on either the upper or 

 lower wall. When the bulb is drawn back by the pharynx, this 

 opening is closed by the roof or floor of the outer case, and the 

 bulb acts as a piston creating a vacuum, and when released, the 

 opening being no longer obstructed, permits the free flow of fluid 

 up the pharynx. Preparations of the following species show the 

 pharyngeal pump : — 



Dolichopus phcmipes Scop. 

 D. griseipennis Stan. 

 Poecilobothrus nobilitatus L. 

 Orthochile niqroccerulca Ltr. 



