54 



THE INTERNAL STRUCTURE OF MUSCA DOMESTICA 



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

 these lateral processes form the primary forceps (p-f-), and lie at 

 each side of the aperture of the male genital atrium (gxi), of which 

 the posterior edge of the sclerite forms the lower or anterior lip. 



V\\\d. 



an. 



y\\.d.- 



VIv 



Fig. 24. The posterior end of the abdomen of the male seen from behind, showing 



the pronounced sinistral asymmetry. 

 V, d. to viii, d. Fifth to eighth dorsal plates or arches. v, v. to viii, v. Fifth to 



eighth ventral plates or arches. an. Anus. g.a. Aperture of genital 



atrium. p.f. Primary forceps. 



The dorsal plates of the sixth and seventh segments lie on the 

 membrane which is tucked underneath the posterior edge of the 

 fifth abdominal segment. The dorsal plate of the sixth segment 

 (vi, d.) is a narrow transverse 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 abdomen. 

 It consists of a spatulate plate on the left side, the anterior or 



