BY VERA IRWIX SMITH. 



515 



(pi), which probal)ly mark the points of insertion, internally, of the segmental 

 muscles, as described by Viallanes (1882, p. 7) . Similar plates are numerous 

 on the eleventh segment, and in the reaion of the anus. The latter is in the 



^mw^ 9 





Text-fig.9. Spii-acle of abdominal segment, and portion of the integument surround- 

 ing it. (x210). 



Text-fig. 10. View of lateral ridge of a segment, showing spiracle on dorsal side, and 

 arrangement of lateral bristles, (x 18). 



Text-fig. 11. Portion of a bristle, broken off its base /'/^^. (x 210). 



form of a longitudinal slit, with thick, stroni;:ly chitinised lips, situated medianly 

 on the ventral surface of the end segment. From it a deep groove runs back- 

 wards to connect with a terminal transverse split (Text-flgs. 2, 8) . 



Bristles. — Long, stiff, black hairs, or, rather, bristles, are present orr all the 

 segments. They are very brittle, and are easily broken off at the base, so that 

 their regular arrangement on the body is best seen on a freshly-moulted speci- 

 men. In cross-section they are circular, and each consists of an outer brownish- 

 coloured sheath enclosing a dark solid core, which extends almost to the tip 

 (Text-fig. 11) . Most of them taper to a fine point. As in the larvae of the 

 genera Sargus, Chloromyia, Microchrysa, and in Pachygaster minutissima Zetr., 

 and Xylomyia maculata Wied., each abdominal segment from the first to the 

 seventh bears a transverse row of six, equally long, backwardly directed bristles 

 on each surface. The dorsal bail's are slightly longer than the ventral, the 

 average lengths in larvae of 2 mm. width being about 0.7 and 0.6 mm. respect- 

 ively. On the dorsal surface they all slope inward, towards the mid-dorsal Ime; 

 those on the ventral surface form groups of three on each side, the three con- 

 verging posteriorly (Text-fig. 8). On each of the lateral ridges of the same 

 abdominal segments is a group of four bristles, in two rows, set diagonally 

 across the ridge, and sloping upwards and backwards from the dorsal side (Te.xt- 

 fig. 10). The two of the anterior row are short and blunt; the other two, 

 which are arrangeil alternately with them, are more than twice as long, and 

 sharply pointed. They are usually longer than the other body bristles, and in- 

 crease in length posteriorly, the longest of them, on the seventh abdominal seg- 

 ment, measuring 0.8 or 0.9 mm. There is a pair of short pointed bristles 

 on the middle of the dorsal surface of the eighth segment, a longer pair on its 

 lateral ridges, and a transverse row of four on the ventral surface. The lower 

 of the two lateral bristles is inserted just at the end of the terminal split. 



