THE SYRPHIDAE OF OHIO 31 



indicated as in the larva, and the head and eyes are simply irregular, angu- 

 lar masses. The antennae and eyes are next differentiated. The'trach- 

 eation and venation of the wing- pads then becomes evident; and finally the 

 segmentation of abdomen, the vestiture, and last of all the adult coloration 

 appear. The thorax is one of the last parts of the body to assume the 

 adult shape and appearance. During this stage the hind leg presents a 

 peculiarity in that the tibia is bent just beyond the middle at an angle of 

 about 1 50 degrees. This shortens the extent of this leg posteriorly"^ 



The pupae of Eristalis spp. differ from the aphidophagous ones in 

 bearing on the prothorax dorso-laterally, the tracheae which lead to the 

 pupal respiratory cornua, (Plate VII, Fig. 146). This is doubtless also 

 the case in the genus Microdon and others. 



The emergence of the adult often takes a considerable time. The 

 newly emerged imago has its wings much crumpled and folded, in area 

 not more than one-fourth as great as when fully expanded. There is a 

 prominent U-shaped loop in the costal margin near the middle. The body 

 is usually much hardened by the time the fly is completely free from the 

 puparium; yet perfect induration, expansion of wings, and coloration are 

 sometimes not acquired (indoors at least) for an hour or more. 



GENERAL CHARACTERS: THE ADULT 

 The different species \'ar>- very much in form and appearance. They 

 are medium to large-sized flies, only a few species being small. The head 

 is alwa>s large, as broad or broader than the thorax; the face excavated 

 under the antennae and projecting below or with a distinct convex tuber- 

 cle near the middle; front never excavated, often swollen. Antennae 

 three-jointed, the third joint variable; usually compressed and with a 

 dorsal bristle, bare or plumose, but sometimes instead of bearing a dorsal 

 arista, the third joint tapers off into a terminal style. Eyes bare or pilose, 

 usually contiguous in the male between antennae and ocelli; ocelli always 

 present, three in number. Thorax moderately large, barrel shaped, with 

 a large scutellum. Tegulae of moderate si/.e. Abdomen varies from 

 slender and linear to clubbed, or short, broadly oval, and flattened; of 

 five or six, rarely four visible segments. Legs usually weak, sometimes 

 strong; the hind femora, especially, often moderately or much thickened. 

 Bristles ( macrochaetae) almost always wanting, the bod\- either bare, 

 thinl>- pilose, or clothed with thick pile. Wings comparatively large; 

 third longitudinal vein (cubitus) never forked; fourth longitudinal vein 

 terminates in the third; three ]>osterior cells; anal cells close before the 

 border of the wing; basal cells large; behveen the third aud fourth lonoi- 

 tudi)ial vents and iicctrly fyantllcl r,'//// Ihcui there is a false or spurious vein, 



