56 



THE INTERNAL STRUCTURE OF MUSCA DOMEf^TICA 



which are united in the mid-ventral line, forming the ventral border 

 of the anal membrane and the dorsal side of the entrance to the 

 genital atrium. 



All the sclerites of the posterior segments except the sixth and 

 seventh are setose. 



Berlese (1902) in his account of the copulation of the house-fly 

 describes the genitalia. From his account of the male genitalia he 

 appears to have missed the narrow dorsal arch of the sixth segment, 

 or what is very probable, he may have mistaken it for the fifth 

 dorsal arch, as he terms the seventh dorsal arch the sixth, and 



viii.v; 



y\w.' 



m.d. 



-apt 



Pig. 26. Dorsal view of the penis and the ventral half of the tenninal abdominal 

 segments. The median portion of the eighth dorsal arch has been removed, 

 leaving the lateral portions attached to the body of the penis (c.pe.) and the 

 ventral arch of the seventh segment (vii, r.). Lettering as in fig. 24. 



describes what I have called the ventral arch of the seventh as 

 the dorsal arch of that segment. This mistake in nomenclature 

 has probably arisen from the fact that he considered the visible 

 portion of the abdomen as consisting of four segments instead of 

 five, in which case the narrow dorsal arch of the sixth segment 

 would naturally be taken for that of the fifth'. 



The Penis (figs. 26, 27) lies internally on the ventral side of 



1 Berlese describes a sinistral asymmetrj' of the posterior segments, but his 

 figures show a dextral asymmetry, a mistake probably in the reproduction of his 

 figures which has escaped the author's notice. 



