7 oo THE GEXERATIl'E ORGANS. 



In the latest stages of the pupa numerous large tracheal 

 vessels are seen covering the convex surface of the ovary and 

 extending through the ovarian cavity into the spaces between 

 the ovarian follicles. 



Some of my sections from pupae about the eighth day 

 (PI. XLIX., Fig. i) exhibit the section of one or more convo- 

 luted epithelial tubes lying in the ovarian cavity at the inner 

 limit of this cavity. I believe that these are sections of the 

 caeca! end of the parovarium. 



In the investigation of the further changes which occur in 

 the ovary it is necessary to have recourse to flies which have 

 been on the wing for some time, and therefore the age of these 

 insects is unknown. Development of the ovary progresses 

 very slowly in these insects when bred and kept in captivity. 



As such insects never unite with the males, there is no cer- 

 tainty that development progresses in the same manner as in 

 impregnated females, and, so far as my experience goes, the 

 ovaries of captive insects are always arrested, and no mature 

 egg-tubes are ever formed. 



In the stage represented in PI. XLIX., Fig. 2, the egg-stocks 

 are divided by superficial constrictions into several segments, 

 usually five or six. The stalk is greatly increased in length ; in 

 some cases it measures as much as '15 mm. in length. The 

 anterior extremities of the egg-stocks are closely surrounded 

 by ovarian stroma, whilst the posterior end and the egg-stalk 

 lie in a well developed ovarian follicle. The ovarian follicles 

 arc now lined by a well-marked epithelial layer, apparently 

 derived from the epithelial tissue which covers the convex 

 surface of the ovary. 



At this period the oviducts spread over the inner margin of 

 the convex surface of the ovary, and are seen in section as a 

 cavity behind the ovary. There is no evidence that the follicles 

 open into this cavity, but at a somewhat later period the con- 

 tinuity between these and the cavity of the oviduct becomes 

 established by the shedding of the epithelial layer of the follicles, 

 hi the adult ovaries I have found no traces of the follicular 

 epithelium. The blind end of the tuba of the oviduct appears 



