THE MAMMALIAN SEXUAL CYCLE 



55 



way, there being some women, perhaps, who do not ovulate 

 spontaneously and in whom consequently no corpus luteum is 

 formed when coition does not take place and no pseudo-pregnant 

 phenomena. It is conceivable also that with man (as is said to 

 be the case with monkeys) there may be certain individuals who 

 experience seasonal sterility, ovulation not occurring at all over 

 long periods. In such women the menstrual destructive changes 



Fig. 33. — Section through the human uterus during the recuperation 

 stage. (From Sellheim.) 



would naturally be less severe, since the process would represent 

 the prooestrum alone. 



The problems relating to the occurrence of oestrus and 

 ovulation in the Primates present some difficulties. It is stated 

 that in the macaque monkey {Macacus rhesus), as well as in 

 other species, coition may take place at any time during the 

 cycle, but the observations were necessarily made upon animals 

 in captivity, and consequently under somewhat artificial con- 

 ditions. As is well known, a similar statement is made about 

 man. There is, however, abundant evidence that with man there 

 are recurrent periods when sexual desire is greater than at other 



