THE SYRPHIDAE OF OHIO tg 



much if there is an}' homology with adult mandibles. All these parts are 

 black, firmly chitinized, and are continued internally into a broad, chitin- 

 ous, esophageal framework, the whole operated by a complex system of 

 muscles. 



The antennae are very short, consisting of a single, fleshy joint with 

 two, minute, rounded segments, side by side, at its apex. The pair of 

 sessile, prothoracic spiracles each have typically a crescentric opening 

 which may be guarded by rounded, tooth-like lobes. 



The posterior respiratory organ, in this type, consists of two, short, 

 cylindrical tubes united along the median line, very slightly divergent at 

 the tip, situated on the dorsum of the last segment which is much depressed. 

 They are firmly chitinized especially at the tip where each tube bears three 

 slit-like spiracles raised on radiating carinae. Dorsally near the middle 

 line, each is marked by a smooth, circular plate. Median to this plate is 

 usually a spur or spine-like projection of the surface, the dorsal spiracular 

 spine, and there are frequently elevations of the surface or other orna- 

 ments between the spiracles, referred to as interspiracular hairs, spines or 

 ridges. 



The colors of these larvae are commonly some shade of brown, pink 

 or greenish marked with black or white. The integument though 

 tough is thin and transparent and the dorsal blood-vessel almost always 

 visible along the median line. 



Of Mesogramma polita, which in the lar\-al stage feeds on the cells 

 and pollen of corn, I have not secured the larvae, but a careful study of 

 puparia found at the Experiment Station Farm, West Raleigh, N. C, 

 has revealed enough about the larval organization to show that the larvae 

 of this habit are superficially quite similar to the aphidophagous ones; 

 the general shape, size, and appearance being the same. Some of the 

 detailed external anatomy, however, shows important differences from 

 the aphidophagous larvae. 



The mouth-parts could be only imperfectly made out but showed the 

 presence of the beak-like arrangement of upper and lower V-shaped jaws 

 (Fig. 191). The posterior respiratory appendage is essentially like that 

 in aphidophagous species but peculiar in having the most dorsal of the 

 spiracular slits with its elevation small and rounded, instead of trans- 

 versely oval like the other two. I could find no trace of the circular 

 plaieso common in the aphidophagous form. There is little ornamentation 

 of the appendage, only a short, inconspicuous, dorsal spiracular spine. 

 The two tubes are somewhat divergent at the tip. A brief discnption 

 of the stages of J/, polila will be found on pp. 66, 67. 



