Discussion 85 



Rowlands: I have no information to offer about mink, but in various 

 species of seals in which implantation is also delayed for some months 

 after mating, Prof. Harrison has described changes in the corpus luteum 

 coincident with implantation. 



Harrison: My impression was, in examining that material, that the 

 corpus luteum of ovulation, if you like to call it that, was not properly 

 vascularized, and that at the time of implantation, perhaps some two or 

 three months later, the corpus luteum became revascularized, and that 

 before implantation there was an outbreak of vacuolation of the luteal 

 cells, which went when implantation occurred. 



Matthews: Something similar seems to occur in the badger also. 



Amoroso: With regard to the persistence of corpora lutea, the cat 

 resembles the guinea pig more closely than any other mammal. In the 

 cat the corpora lutea of pregnancy persist throughout gestation and 

 involute rapidly only after parturition. Consequently, should a new 

 pregnancy be established early in the post-partum period two genera- 

 tions of corpora lutea are recognizable in the ovaries, one set from the 

 preceding pregnancy and a new set for the concurrent pregnancy. In 

 these circumstances the older set, coming under the dominance of the 

 same endocrine influences as the new set, show signs of resurgence and 

 follow the same growth pattern as the latter; never, however, do they 

 again attain their former maximum size. In the cat the corpora lutea 

 attain their maximum size during the period of implantation, so it may 

 well be that Blandau's figures for the guinea pig covering the period 

 sixth day to twelfth day may actually represent the era when the ovum 

 is actually entering the endometrium. 



Accessory corpora lutea, such as are found in the mare, are sometimes 

 encountered in the ovary of pregnant cats during the seventh week of 

 gestation. 



