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 Httle 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 TipuUnae there are present on the abdominal segments rectangular 

 areas of impressed punctures on either side of the median hne, 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, 



