THE HORMONES IN HUMAN REPRODUCTION 



change, namely menstruation, the two phenomena were 

 thought to be the same. Serious misconception of the human 

 cycle caused by this error has been cleared up only in the 

 twentieth century. 



For the sake of perfect clearness on this point, let us com- 

 pare diagrams of the estrous and the menstrual cycles (Fig. 



THE CYCLE IN GENERAL 



ESTRUS 



CORPUS LUTEUM 



PRIMATE CYCLE 



OVULATION 



-I- 



MENSTauATION 



Fig. 16. Diagram comparing the estrous cycle in general with the 

 menstrual cycle of the higher primates. 



16) . It will be seen that the two are fundamentally alike, since 

 the important feature of each is ovulation followed by the 

 corpus luteum phase. In lower animals ovulation is accom- 

 panied by an outspoken period of sexual receptiveness, in the 

 primates (man, apes, and higher monkeys) it is not; in the 

 primates the end of the corpus luteum phase is accompanied 

 by menstruation, in the other animals there is no bleeding at 

 this time. 



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