No. 64] DIPTERA OF CONXECTICUT : MORPHOLOGY 101 



the lateroverted sixth and seventh sternites Qs and 7s becomes less 

 clear, as these sclerites lose their sharpness of outline. The helomy- 

 zids appear to follow their own path of specialization within the 

 family, but the helomyzid Anorostouia furnishes some excellent clues 

 for interpreting the modifications occurring in the next stage of the 

 series represented by the anthomyid Hylemyia. 



In the helomyzid Anorostoma (Fig. 13, C), the lateroverted sev- 

 enth sternite Ts drags along the asymmetrical sixth sternite 65 by one 

 corner, as it becomes adherent to the inverted eighth sternite 86* (from 

 which it is still demarked by a suture), and in the anthomjdd Hyletn- 

 yia (Fig. 13, D), the seventh sternite 7s, to which the sixth sternite 6.<? 

 tends to become attached by one corner, becomes still more closel}' 

 adherent to the inverted eighth sternite Ss (from which it is still de- 

 marked by an incomplete suture). Although the sinistral spiracle of 

 the seventh segment enters the upper corner of the seventh sternite Ts 

 behind it, in HyJemyia (Fig. 13, D), it does not do so in Anorostoma 

 (Fig. 13, C), in which the seventh spiracle is not borne in a tergite. 

 so that the presence of the sinistral seventh spiracle in the upper 

 corner of the seventh sternite 7s of Hylemyia (Fig. 13, D) cannot be 

 cited as positive proof that the seventh tergite forms a part of the 

 sclerite labelled T^' in Fig. 13, D, of Hylemyia, althougli from other 

 evidence this may be the case (e. g., thfe presence of the sinistral sev- 

 enth spiracle in the vestigial tergite 7t of the insects shown in Fig. 

 14, A and C). 



The next stage in the series is illustrated by the calliphorid 

 Phormia r-egina. shown in Fig. 13. E, in which the suture between the 

 vestigial seventh sternite 7s and the inverted eighth sternite 8.s be- 

 comes obliterated, although its former course is indicated by a faintly 

 impressed line indicated by a dotted line in Fig. 13, E. The union 

 of the seventh sternite with the inverted eighth sternite to form a 

 synsternite is now complete, but the fact that the sinistral spiracle of 

 the seventh segment remains close to the anterior border of the syn- 

 sternite indicates that the seventh sternite does not contribute much 

 to its area. 



The asymmetrical sixth sternite 65- of Fig. 13, E, (which borders 

 the genital pouch, or cubiculum, phc of Fig. 14, F, into which the 

 aedeagus pha is thrust in repose) now becomes more closely associated 

 with the synsternite 7s-\-^s than with its own tergite 6^, and in fact 

 the sixth sternite G.5 is interpreted as the sternite of the eighth seg- 

 ment by Snodgrass (1935) who regards the synsternite as the eighth 

 tergite in the closely related fly Pollenia rudis. If, however, we trace 

 the modifications of the sixth sternite 6s of Phormia regina^ (Fig. 

 13, E) back through the successively less modified stages in the 

 series shown in Fig. 13, D, C and B. to a similarly modified syr- 

 phid such as Paragus, shown in Fig. 13, A, and then trace the parts 

 on back to a less modified syrphid such as Scricomyia shown in Fig. 

 12, F, in which the sixth sternite Qs is clearly recognizable as such, 

 and retains its normal relations to the sinistral sixth spiracle and the 

 sixth termite (^f above it, the conclusion that the sclerite labelled 6-9 



m.' 



