THE HYPOPYGIUM OF THE DOLICHOPODID^. 



BY ROBERT E. SNODGRASS. 



Plates XXX-XXXIII. 



The term hy-popygium as used by the writer refers to 

 the ninth abdominal segment of the male. This is the seg- 

 ment that carries the intromittent organ and the clasping 

 and pther organs of copulation. 



In the Diptera the hypopygium is nearly always more or 

 less conspicuously enlarged and variously modified to sub- 

 serve the purpose of coition. 



The tenth segment is the segment that carries the anus, 

 and is usually comparatively small and inconspicuous. It 

 may, however, bear expanded or elongate lobes of various 

 shapes. Such lobes are nearly always soft and flexible, 

 and probably have no direct connection with the genital 

 function of the ninth segment. 



The segments immediately preceding the ninth are usually 

 modified in a manner dependent on it. They may form a 

 peduncle for the hypopygium; they may be distorted in 

 shape and asymmetrical ; they may be variously reduced 

 and some of them even lacking. 



Segments i to v or vi usually constitute the normal 

 or pregenital part of the abdomen. 



The writer is indebted to Professor J. M. Aldrich of the 

 University of Idaho for named material on which the fol 

 lowing descriptions are based. 



The hypopygium of the Dipteran family Dolichopodidas 

 usually has the form of a laterally compressed oval or ovate 

 capsule carried upon a flexible peduncle. The ventral part 

 is deeply concave, the cavity thus produced being the gen- 

 ital chamber. From the anterior part of the roof of the 

 genital chamber arises the penis. This is elongate and 



[273] September 28, 1904. 



