SEXUAL PERIODICITY IX THE FEMALE MAMMAL 21 



ovariectomy, have been described, especially for the human, b}^ 

 many writers. 



The fading out of the sexual cycle at the menopause is far less 

 abrupt and regular than is its appearance at puberty. In the 

 human, the menopause extends over two or three years, 

 menstruation gradually becoming less frequent and less regular. 

 According to Magian (433) the cessation of menstruation does 



'.C.I. 



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Fig. 13. — Ovary of Senile Mouse 15 months old, showing 

 LACK of Follicles and New Corpora Lutea {cf. fig. i). 



O.C.I, old corpus luteum; s.a.f. small anoxular follicle. 



not necessarily involve the complete disappearance of fertility, 

 and the ovarian cycle may therefore go on longer than the 

 uterine. 



Data relating to the menopause in lower mammals are very 

 difficult to obtain. Domesticated animals are usually slaugh- 

 tered when the breeding function declines, and in laboratory 

 animals the decreased resistance to disease which occurs in old 

 age usually results in death about the time when menopause 

 symptoms appear. Nevertheless some data are available. 



