TYPES OF (ESTROUS CYCLE 



55 



become embedded and are reabsorbed. This sterility set up by 

 lactation in the rabbit is clearly a continuation of the conditions 

 found in the rat and mouse, where lactation causes a delay in the 

 implantation of the blastocysts, but not a permanent inhibition 

 Sterile copulation in the rabbit is followed by a condition of 

 pseudo-pregnancy, during which the changes in the ovary, 







Fig. 28. — Photograph of Mammary Gland of 

 Pre-Pubertal Rabbit. 



The gland is limited to a few ducts around the nipple. 

 (After Hammond). 



the uterus, and the mammary glands are similar to those 

 occurring during the first half of pregnancy. Pseudo-preg- 

 nancy in the rabbit, though not so prolonged sls in Dasyurus or 

 the ferret, is nevertheless a far more distinct phase than the 

 pseudo-pregnant period in the mouse and the rat. The female 

 rabbit is atypical among lower mammals in allowing copula- 

 tion at other times than oestrus (264). 



The ovarian cycle consists in the maturation of Graafian 

 follicles at the beginning of the breeding season and persistence 

 of mature follicles until copulation takes place, or until the 

 breeding season ends. In the absence of mating, atresia sets in 

 at the end of the breeding season. Ovulation takes place about 



