56 WALTER HEAPE. 



ceases, may be still in progress at the time coition is per- 

 mitted by the bitch (Millais). 



The Moor macse in the Zoological Gardens has a definite 

 oestrus, which always occurs shortly after the menstrual 

 discharge ceases, and which lasts for two or three days ; and 

 there is strong reason for believing this is also the case with 

 various other monkeys, as, for instance, the orang-utang 

 (Ellis) . 



The human female frequently experiences oestrus with 

 marked strength after menstruation is over (Martin, 1888), 

 more especially, it would appear, in those individuals who 

 do not suffer from excessive menstruation, — in other words, 

 in those whose generative system is least disturbed by the 

 consequences of civilisation and social life. This special 

 time for oestrus, in the human female, has very frequently 

 been denied, and no doubt civilisation and modern social 

 life do much to check the natural sexual instinct where 

 there is undue strain on the constitution, or to stimulate 

 it at other times, where extreme vigour is the result. 



For these reasons a definite period of oestrus may readily be 

 interfered with, but the instinct is, I am convinced, still 

 marked. Ellis quotes various authors who bold a similar 

 view, but they do not all agree as to the time when oestrus 

 occurs ; if, therefore, the views which I have advocated here 

 are correct, it would seem probable that abnormal oestrus 

 has been mistaken for true oestrus in many of these cases. 



Summary and Conclusion. 



Introduction. — After criticising the terms commonly 

 used to denote the various stages of the '^ sexual season" of 

 mammals, I have defined the terms used in the present 

 paper. 



Female mammals are divided into two classes, " monoes- 

 trous " and " polyoestrous " mammals, and I have explained 

 that, in the absence of the male, " pro-oestrum," " oestrus," 

 and " raetoestrum " are followed by " dioestrum " in polyoes- 

 trous mammals, during the recurrence of the '' dioestrous 



