No. 64] DIPTERA OF CONXECTICUT : MORPHOLOGY 73 



beai'inj;:^, terminal region called the telson. The telson is usually re- 

 duced to a membranous region around the anal opening, and the elev- 

 enth abdominal segment tends to unite with the tenth even in the 

 orthopteroid insects, so that it is not surprising to find a similar 

 tendency exhibited by some of the lower Diptera, although some of 

 them retain traces of an eleventh abdominal segment, as is the case 

 in the female tipulid shown in Fig. 9, A. 



The abdominal segments are best preserved in female Diptera; 

 and in some of the primitive Nematocera, such as the tipulids, etc., 

 the abdomen has its full quota of typical segments, with a pair of 

 spiracles in each of the first eight abdominal segments. The onto- 

 genetic development of these Diptera very conclusively shows that the 

 thoracic region contains only three segments (i. e., the pro-, meso-. 

 and metathorax) in these forms, and none of the basal segments of 

 the abdomen enters into the composition of the thorax, as is erron- 

 eously claimed to be the case by Berlese (1909), Metcalf (1921), Bal- 

 four-Browne (1932), and others, who regard the apparent first ab- 

 dominal segment in the Diptera as the true second or third segment 

 of the abdomen. 



Nine visible segments, followed by an inconspicuous anus-bear- 

 ing segmental complex, called the ''anal segment" or proctiger, are 

 frequentlj'^ present in the abdomen of male Diptera. The first seven 

 of these segments may bear spiracles, although no spiracles have 

 been found in the eighth abdominal segment of any male Diptera. 



A reduction of the abdominal segments may take place in both 

 sexes, (a) by the coalescence of the first two tergites in the basal 

 region of the abdomen to form a syntergite, or composite apparent 

 first tergite, and (b) by the fusion of the greatly reduced tenth and 

 cercus-bearing eleventh segment (with which the anus-bearing telson 

 had united) to form the proctiger: but the reduction of the segments 

 in the other regions of the abdomen is not the same in the two sexes. 



Huckett (1924) considers that the sixth and seventh abdominal 

 segments have fused in the females of the higher Diptera in which 

 the sixth segment bears two pairs of spiracles (as in Fig. 9a, D), and 

 consequently maintains that the female gonopore {fg of Fig. 9a) lies 

 behind the ninth, instead of behind the eighth sternite in these Dip- 

 tera, unlike the rest of their allies. If one examines the series of 

 female Diptera shown in Fig. 9a, B, C and D (in which the segments 

 and parts correspond in every way), it is evident that the spiracles of 

 the seventh segment, 7sy>, leave the seventh segment behind tiiem when 

 they migrate into the posterior region of the sixth segment, and the 

 spiracles of the sixth segment, 6^;^, move slightly backward to join 

 them in i\\Q sixth tergite, 6;^ of Fig. 9a, D, which is therefore not the 

 fusion product of two tergites, so ^that there is no fusion of segments 

 in the postabdomen of these Diptera, although a fusion of another type 

 may occur in the postabdomen of the female Diptera shown in Fig. 

 IO.'F, or Fig. 9, D, etc. 



A type of segmental reduction wholly different from that occur- 

 ring in the abdominal region of anv female Diptera takes place in 



