STEUOTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-FLY. 433 



This sclerite is, no doubt, of great assistance in propelling 

 the seminal fluid along the ejaculatory duct during copula- 

 tion. A short distance behind the ejaculatory sac the duct 

 opens into the penis. 



The Male Gonapophyses. — The extremity of the 

 abdomen in the male (fig. 10) has undergone considerable 

 modification in the formation of the external genitalia. The 

 visible portion of the abdomen, as seen from above, consists 

 of the first five abdominal segments; the remaining three 

 segments are slightly withdrawn into the fifili segment, and, 

 on looking at the abdomen from the posterior end, only the 

 terminal segment, the eighth, surrounding the anus, can be 

 seen. The sixth and seventh segments have been greatly 

 reduced. The sternal portion of the fifth segment consists 

 of a cordiform sclerite {V.v.), the apex of which is directed 

 forwards, and each of the lateral margins of the base is 

 produced to form a short process, swollen at the tip — these 

 lateral processes form the primary forceps (jh/.), and lie at 

 each side of the aperture of the male genital atrium (g.a.), of 

 which the posterior edge of the sclerite forms the lower or 

 anterior lip. The dorsal plates of the sixth and seventh 

 segments lie on the membrane, which is tucked underneath 

 the posterior edge of the fourth abdominal segment. The 

 dorsal plate of the sixth segment (vi, d.) is a narroAV, trans- 

 verse sclerite ; its lateral edges, which do not extend down 

 the sides, are slightly produced anteriorly. The ventral 

 plate of the sixth segment (vi, v.) is asymmetrical, and, with 

 the dorsal plate of the seventh segment, produces a pro- 

 nounced asymmetry of the posterior end of the male abdo- 

 men. It consists of a spatnlate plate on the left side, the 

 anterior or ventral side of which is produced into a narrow 

 bar extending across the ventral side of the aperture of the 

 genital atrium, its distal extremity bifurcating. The dorsal 

 plate of the seventh segment (vii, d.) is asymmetrical. It 

 consists of a narrow sclerite, which, on the dorsal side, is 

 similar to the sixth dorsal plate, but the left side (see fig. 5) 

 extends down the side, and broadens out into a somewhat 



