46 



INTERNAL SECRETIONS OF THE OVARY 



the beginning of vaginal cornification. The passage of the ova 

 down the tube is facihtated in both animals by the accumulation 

 of fluid in the periovarian cavity at oestrus. During the next 

 two days the corpora lutea develop, and in the unmated normal 

 rat they attain their maximum growth about three days after 

 oestrus. This set of corpora lutea may be distinguished histo- 

 logically from the previous sets without the aid of vital staining, 

 but the previous sets can only be separated reliably by means of 

 this technique, or by special histological examination of the 



Fig. 20. — Uterus of Mouse : (a) during Dicestrus, (b) during 

 (EsTRUs, showing typical distension of Uterus and Ovarian 

 Capsule during Qistrus. 



lutein granules. According to Long and Evans, degeneration can 

 be detected by the latter technique in the new corpora lutea at 

 the beginning of the next oestrus. During pseudo-pregnancy 

 growth of the follicles is postponed until about the usual time 

 before the next oestrus. This postponement of growth is un- 

 doubtedly brought about by the activity of the corpora lutea, 

 which undergo greater development during pseudo-pregnancy 

 than in unmated animals. In the same way ovulation is entirely 

 inhibited during true pregnancy, and follicular maturation, 

 beginning when the corpora lutea atrophy just before parturi- 

 tion, is completed only in time for the post-partum ovulation. 

 No ovulation takes place between the oestrous period occur- 

 ring immediately after parturition and that marking the end 

 of the lactation dioestrus. 



Uterine cycle. The uterine cycle in both the mouse and rat is 

 closely synchronized with the ovarian cycle. During dioestrus 



