THE MENSTRUAL CTCLE 



This states that menstruation is simply the downfall of the 

 premenstrual (progestational) endometrium, and that it 

 is caused by the degeneration of the corpus luteum. It will 

 be seen that this theory fits all that has been said about the 

 primate cycle thus far, and that it is compatible with our 

 diagram. Fig. 22. According to this theory, the endometrium 

 cannot menstruate unless it is first built up to the "pre- 

 menstrual" state. Professor Meyer put this into an aphorism 

 which was much quoted by the gynecologists "Ohne Ovula- 

 tion keine Menstruation" — without ovulation there can be 

 no menstruation. 



This is a beautiful, clear hypothesis, and it is half true. 

 It is also, unfortunately, half false. The fallacy is subtle 

 but fundamental, and leads us headlong into a mass of un- 

 solved problems. 



Anovulatory cycles. The failure of the German theory of 

 the cycle is a matter of especial interest to me, for it was 

 my lot to obtain (to my great perplexity) the first undeniable 

 evidence against it. The story is best told as it happened. 

 In 1921, after several years of work on the cycle of the 

 domestic pig, I felt prepared to begin a study of a menstru- 

 ating animal and for this purpose I chose the Rhesus monkey. 

 Practically nothing was known on the subject. There had 

 been two investigations. Walter Heape, a distinguished Eng- 

 lish biologist, had gone to India more than twenty years 

 before to study reproduction in Rhesus monkeys and langurs, 

 but illness had forced him to return to Cambridge, where 

 he followed and described the cycles of a few animals he had 

 taken home with him. M. A. Van Herwerden had studied 

 material of a wholly different kind. Hubrecht, the great 

 embryologist of Utrecht, had collected a great many repro- 

 ductive tracts (uteri with ovaries) from several species of 

 monkeys. These had been obtained largely by Dutch colonial 

 officers in the East Indies. Miss Van Herwerden examined 

 these specimens, which were unaccompanied by life histories 



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