100 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 



Fio-. 10. H). The sclerite It interpreted as the seventh tergite in Fig. 

 14rA, of Microiieza^ apparently becomes reduced to the small area 

 labelled It in the upper region of the seventh sternite 7s, which be- 

 comes adhei-ent to the inverted eighth sternite 85 in Fig. 14, C, of 

 Calohata. The structures in the ventral region of these insects pre- 

 sent some very curious modifications, especially in the region of the 

 fifth sternite. 



In the insects shown in Fig. 13, B,C,D, E and F, the sixth tergite 

 6?^ becomes greatly reduced (and may be lost in some of them) , but the 

 sixth tergite is not appreciably displaced by the torsion process during 

 whicli the sixth sternite 6s (bordering the genital pouch) becomes 

 asymmetrically developed and is eventually captured bj^ the S3nister- 

 nite (formed by the union of the latero verted seventh and inserted 

 eighth sternites), so that the sixth sternite then appears to be the 

 .sternite of a "tergite"' formed by the inverted synsternite, as in Fig. 

 13, F. It is not clear where this series begins, but the condition ex- 

 hibited by the caelopid Gaelopa^ shown in Fig. 12, H, makes a fairly 

 good starting point for tracing the development of the parts in the 

 series, although Caeloya has many modifications of its own, appar- 

 ently leading oil' along another line of development. 



It is interesting to note that the dextral spiracles of the sixth 

 and seventh segments of Caelopa (Fig. 12, H), are shifted down and 

 around into the insect's left side, and the sixth tergite 6^ apparently 

 follows its dextral spiracle around in the shift, while a small plate 

 whicli may be a vestige of the seventh tergite, also follows its dex- 

 tral spiracle around into the insect's left side, thus indicating the 

 intensity of the torsion, which is also indicated by the profound dis- 

 tortion and displacement of the sixth and seventh sternites 6s and 7s. 

 as these follow the inverted eighth sternite 8s in the upAvard shift of 

 the sternites. The ninth segment has almost completed its circuni- 

 version in Caelopa, but has not yet become rigid, as it does in the 

 higher Cyclorrhapha in which the circum version is practically com- 

 pleted. 



In the series of insects shown in Fig. 13, the parts are retained 

 m a fairly primitive condition by the helomyzid Neoleria, shown in 

 Fig. 13, B. in which the sixth tergite 6^ is fairlv larire and remains 

 practically undisturbed while its asymmetrical, lateroverted sternite 

 6s becomes attached by its upper corner to the lateroverted seventh 

 sternite 7s, which in turn is attached by its upper corner to the in- 

 verted eighth sternite 8s (as though the sternites were being pulled 

 along m a string), and the relations of these lateroverted sternites to 

 each other is much the same as in Fig. 13, A of the syrphid Paragus, 

 or lig. 12, H, of Caelopa. The fate of the seventh tergite in Fig. 

 13, B, is not clear, unless it becomes vestigial and fuses along the 

 anterior border of the inverted eighth sternite 8s when its sternite 7s 

 is captured by the eighth sternite. 



In the helomyzid Aviorostomn shown in Fig. 13, C, the union of 

 the sixth, seventh and eighth sternites is carried a step further; and 

 in the helomyzid SuUlia shown in Fig. 14, D. the distinction between 



