No. 64] DIPTERA OF CONNECTICUT : MORPHOLOGY 75 



Cyclorrhapha, and is considered to be of some taxonomic importance 

 by Young. 



A feature of the basal abdominal segments which might give 

 rise to some confusion in counting the segments in this region of the 

 abdomen is the tendency for the first tergite to become subdivided 

 into an anterior and posterior region by the formation of a second- 

 ary transverse suture in such Diptera as Simuliu?n, or by a trans- 

 verse strip of membrane, as in Sciara and in the stratiomyid Allog- 

 nosta. The second tergite is similarly subdivided in the bibionid 

 Plecia^ in which the second sternite is likewise subdivided by a trans- 

 verse membranous region; and similar secondary subdivisions of the 

 second sternite occur in the tipulid Pachyrhina, in the empid Rhmn- 

 phomyia, and in the calobatid Calohata., etc. 



J'he Preahdomen and Postdbdomen. The abdominal segments 

 posterior to the fifth are not, as a rule, very greatly modified in the 

 Nematocera, but the rest of the Diptera exhibit an increasingly marked 

 tendency for the segments behind the fifth to become reduced and 

 slender, with the result that the abdomen may eventually become 

 divided into a preabdomen, which is usually composed of five abdom- 

 inal segments, which are broader and more strongly sclerotized than 

 the rest, and a postabdomen, which is frequently quite slender, and 

 its segments may become telescoped into the preceding ones, or they 

 may be concealed by the segments of the preabdomen. 



The postabdomen of the females of the Diptera usually serves as 

 an egg-laying tube; and in the higher Diptera, the postabdomen of 

 the female usually plays an active part in the mating process, as is 

 described in the mating of the housefly by Berlese (1902). The post- 

 abdomen of female Cyclorrhapha is not asymmetrically developed, 

 as is the case in the segments of the postabdomen of the males of the 

 higher Diptera, but the postabdomen may become highly modified in 

 certain female Cyclorrhapha, 



In male Cyclorrhapha the fifth abdominal segment frequently 

 forms the last segment of the preabdomen, as it does in the females, 

 j but the coalescence of the first two tergites in the basal region of 

 I the abdomen may make it very difficult to count the segments properly, 

 \ unless they are counted in the sternal region, where the sclerites usually 

 remain distinct (although the first sternite may be small). The 

 sternites of the preabdomen of such muscoid flies as Stomoxys may 

 become reduced to small sclerotized plates or "islands" embedded 

 in the broad ventral membrane; and the character of these plates is 

 used as a feature of taxonomic importance by Girschner, and other 

 students of these flies. 



The fifth abdominal segment is not always the last segment of 

 the preabdomen in male Cyclorrhapha, since Cole (1927) states that 

 in some cases the preabdomen may be reduced to three segments; 

 and in males of such Syrphidea as the one shown in Fig. 12, F, the 

 fourth is the last segment of the preabdomen. In other types of 

 Cyclorrhapha, such as the male calobatid shown in Fig. 14, C (com- 



