THE " SEXUAI) season" OP MAMMALS. 61 



and I have callud it the dioestrum ; but where it serves to 

 separate two sexual seasons it persists for a considerable 

 length of time, and I have called it the anoestrum. 



The pro-oestrum is always associated with hypertrophy aud 

 congestion of both external and internal sexual organs and 

 the uterus, and with a discharge from the generative orifice. 

 These phenomena are common to all mammals ; they may, 

 however, be further complicated. These complications may 

 include rupture of the congested vessels of the hypertrophied 

 superficial uterine mucosa, and extravasation of the blood 

 contained therein ; they may include a discharge of this blood 

 into the uterine cavity, and from thence to the exterior; and 

 even more or less denudation of the mucosa may take place, 

 leading to the formation of a menstrual clot. 



The rupture of the vessels of the mucosa and the subse- 

 quent phenomena are not experienced by all mammals; they 

 are supplementary to the essential factors of pro-cestrum, and 

 occur in part rarely in some animals, in part always in some 

 animals, and in a complete sequence only, so far as is known, 

 in Primates. 



That the pro-cestrum of Primates is identical with the pro- 

 cestrum of other mammals does not, however, admit of any 

 doubt ; there is ample evidence of this in the various inter- 

 mediate conditions of other mammals, by means of which, 

 and bearing in mind the influence of domestication and 

 civilisation on polyoestrum, the evolution of the menstruation 

 of monkeys and of the human female from the pro-cestrum of 

 the lower mammals can be surely traced. A further evidence 

 of this is the time of the occurrence of oestrus. It is mani- 

 fested at a certain period after pro-oestrum, and has a certain 

 relation to it — that is, it follows and is not coincident with 

 pro-oestrum in the lower mammals, as is usually supposed. 



In some monkeys the same relation of oestrus to pro-oestrum 

 obtains, and in others it is probably so, while in the human 

 female there is evidence of a similar condition, especially, 

 probably, among normally strong individuals who lead a 

 healthy life. 



