DIPTERA 



831 



The antennce vary greatly in form, in some genera the flagellum 

 s long and consists of several quite distinct segments (Fig. 1061) in 

 others it is short with but few indis- 



#tinctly separated segments and with 

 an arista (Fig. 1062) as in the True 

 Brachycera. 

 The most distinctive characteris- 

 tic is the peculiar venation of the 

 wings (Fig. 1063). The branches of 

 vein R are crowded together near the 

 costal border of the wing ; and the first 

 omyta. cell M2 is unusually short and broad; 

 the branches of vein M and vein Cui 

 are comparatively weak, and the tibiae are with- 

 out spurs. 



These flies are found on flowers and leaves, especially in the vi- 

 cinity of water, and in bogs and marshes, but some species are 

 found far from water. 



The larvas occur in various situations; some are aquatic and 

 feed upon algse, decaying vegetable matter, and small Crus- 

 tacea; some live in privies, in cow-dung, and in other decaying 



Fig. io6o.- 



Strati 



Fig. 1062. 



Fig. 1063. — Wing of Stratiomyia. 



matter; some are found under bark of trees that has become slightly 

 loosened and feed upon sap and upon insect larvse; and some have 

 been found in nests of H^Tnenoptera and in those of rodents, where 

 they act as scavengers. 



The larvffi are spindle-form or elliptical and flattened, and with 

 the surface of the body finely shagreened. The posterior pair of 

 spiracles is situated in a cleft or chamber at the end or near the end 

 of the body. In the aquatic forms the apical respiratory chamber is 

 furnished along its margins with long plumose hairs. When the larva 

 is at rest hanging from the surface of the 

 water these hairs are spread radiatingly upon 

 the surface film; they thus form a means of 

 support and prevent the water from enter- 

 ing the respiratory chamber. Fig. 1064.— Pupariura of 



The aquatic species leave the water to Odontomyia. 



