870 CHARLES PauL ALEXANDER 
The abdomen 
The abdomen, the third and last region of the body, lies behind the 
thorax and is attached to the caudal parts of the metathorax. It is com- 
posed of nine apparent segments, or annuli, numbered from the basal 
(first) to the terminal (ninth). Each of these segments consists of three 
regions —a dorsal sclerite, the tergite; a ventral sclerite, the sternite; 
and a lateral region on either side, the pleurites, these being either integu- 
mentary or chitinized. The abdominal spiracles are located in this 
pleural conjunctiva. There is but little modification of the general 
type in the various groups of crane-flies. 
The first segment is very short and appears as a narrow ring closely 
attached to the metathorax; the second is the longest of the segments; 
the remaining segments are subequal in size, or, in the male sex especially, 
shortened and crowded toward the end of the abdomen. In many species 
of Tipulinae there are present on the abdominal segments rectangular 
areas of impressed punctures on either side of the median line, which 
on the second tergite are about midlength of the sclerite and on the 
succeeding tergites are on the basal part; often there are smaller areas 
of punctures nearer the caudal margin of the sclerites. These areas 
are usually present on the sternites as well as on the tergites. The sexual 
organs are borne at the end of the abdomen in both sexes. 
The male hypopygium.— The hypopygium, or propygium, of the 
male sex is of extreme importance in the determination of species. In 
many groups and genera (Gonomyia, Molophilus, Tipula, and others) 
it is almost impossible to identify the species without considering the 
details of structure of the male genitalia, and in these groups the hypo- 
pygium is of paramount importance in specific determination. 
The structure of the hypopygium is relatively uniform and homologous 
thruout the crane-fly series. The organ has been discussed in considerable 
detail by previous authors, especially by Snodgrass (1904), whose termi- 
nology is adopted in this paper. The European authors still adhere 
largely to the cumbersome terminology of Westhoff (1882). 
In the generalized species the hypopygium shows but little complexity 
and enlargement, the terminal segments of the abdomen being of approxi- 
mately the same size and diameter as the preceding segments. In the 
specialized species of many genera (Gonomyia, Limnophila, Tipula, 
