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Scientific Proceedings (132) 



223 (2183) 



Types of mammalian ovary. 

 By LEO LOEB (by invitation). 



[From the Department of Comparative Pathology, Washington 

 University, St. Louis, Mo.] 



We can distinguish among mammals at least three types of 

 ovaries. They are represented among the rodents by the ovaries 

 of the guinea pig, rat and rabbit. 



(1) . In the first type, that of the guinea pig, in the oestrus 

 period, preceding ovulation by a number of hours, the large 

 majority of all follicles — all but the very small ones — begin to 

 degenerate. In the larger follicles the granulosa becomes 

 karyorrhectic en masse and connective tissue begins to grow into 

 the follicular cavity after the destruction of the granulosa epithe- 

 lium has progressed still further. In smaller follicles the proc- 

 ess of destruction of the granulosa is less obvious and the granu- 

 losa cells disappear and here also connective tissue soon begins 

 to invade the cavity. In the week following ovulation the very 

 small follicles develop again and pass through their cycle; about 

 eight days after ovulation the follicles have again reached full 

 size and maturation on the one hand and atresia on the other 

 hand can set in; this atresia usually affects only the large follicles. 



(2) . In the second type, that of the rat, ovulation is not 

 preceded by a general atresia of follicles, but the large follicles 

 mature, rupture and become converted into corpora lutea. There 

 takes place throughout the cycle a limited atresia of follicles. 

 In the rat the ingrowth of connective tissue into the atretic fol- 

 licles is less active than in the guinea pig, in consequence of 

 which the cavity of the degenerating follicle remains preserved 

 during a longer period of time in the former species. In both 

 guinea pig and rat ovulation is spontaneous. It occurs as soon 

 as follicles have had a chance to mature and the inhibiting in- 

 fluence of the corpus luteum has ceased to exert itself. In the 

 guinea pig a considerably longer period is necessary for the 

 maturation of the follicles than in the rat, because in the former 

 additional time is needed to allow follicles to develop from very 

 small to large size, while in the rat only the very large follicles 

 are destroyed at the time of ovulation and therefore maturation 



