74 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bllll. 



the postabdomen of most male Cyclorrhaplia, in which the tergites 

 of the seventh and eighth segments become vestigial or atrophied, 

 and their displaced sternites coalesce to form a synsternite (or syniir- 

 ite), with which the displaced sixth sternite may also unite, as in Fig. 

 13, C, or Fig. 14, D (compare also Fig. 12, I) ; and the sixth tergite 

 may also become obliterated, as in Fig. 14, B, although no comparable 

 reduction takes place in the segments of the abdomen of the females 

 of these Diptera. 



Modifications of the Basal Segments of the Abdomen. Young 

 (1921) has figured the basal abdominal segments of many of the 

 different types of Diptera, and some of these illustrate quite well the 

 tendencies toward a fusion of the basal segments exhibited by certain 

 of the higher Diptera. Starting with the condition exhibited by 

 many tipulids, chironomids, etc., in which the first abdominal seg- 

 ment is distinct and well developed, a comparison with the basal 

 abdominal region of such empids as Rhampho/nyia, or such neme- 

 strinids as Hirmoneura, shows that there is a marked tendency for 

 the first segment to become reduced in comparison with the second 

 segment; and in the scenopinid Scenopinus, the reduced first abdom- 

 inal segment, which is distinct from the second dorsally, exhibits a 

 marked tendency for its tergite to unite with the second tergite 

 laterally. In the helomyzid Leria, the first tergite has united with 

 the second tergite to form a syntergite, but the areas belonging to 

 the two tergites are marked off by a transverse suture and by an 

 incision on each side at the lateral ends of the transverse suture. In 

 the chloropid Ghlorops^ the incomplete transverse suture fades out 

 dorsally, but extends upward for a short distance above the incision 

 on each side. In the ephydrid Parydra., only a deep incision remains 

 between the uniting first and second tergites, while in the platypezid 

 Platypeza^ merely a slight notch on each side is left to show where 

 the former division between the first and second tergites occurred, 

 although the spiracles of the two segments still remain distinct. The 

 series described above, and numerous others, serve to illustrate how 

 the first abdominal tergite unites with the second in the Cyclorrha- 

 pha; and when the apparent first tergite bears two pairs of spiracles 

 in these Diptera, it clearly indicates that the areas in which the 

 spiracles are located were originally parts of two distinct segments. 

 A corresponding fusion of the first and second sternites is extremely 

 rare, although Young (1921) records its occurrence in the tabanid 

 Chrysops indAis. 



Closely associated with the tendency for the first two tergites 

 to coalesce is the tendency for the formation of a latei-al suture "(one 

 on each side) extending from the latero-cephalic margin of the first, 

 tergite into the anterior region of the second tergite. The suture, 

 labelled adv in Fig. 6, C, is called the adventitious suture by Young" 

 (1921), who states that it is less highly developed in the calypterate 

 than m the acalypterate Cyclorrhapha. It has been observed onlv in the 

 conopid Alyopa vesiculosa outside of these two groups of "^ higher 



