110 THE PHYSIOLOGY OF REPRODUCTION 



derivatives of the corpuscles are carried in the form of pigment 

 to the more superficial area by wandering cells. Kazzander,i 

 however, does not admit the agency of leucocytes ; but the most 

 recent observations support Bonnet's conclusions, excepting 

 that (as previously stated) the extravasation which takes place 

 during the destruction period is in the superficial mucosa rather 

 than in the deeper tissue. Thus, although leucocytes are pro- 

 bably involved in the process of pigment formation, there is no 

 need to assume that they carry the extravasated corpuscles to 

 the region where pigment is most abundant. Sometimes the 

 interior of the uterus appears superficially to be -perfectly black 

 with pigment, but in such cases the pigment is, no doubt, de- 

 rived from blood which had been extravasated during a series 

 of procestrous periods, and not merely during the most recent one. 

 Assheton ^ states that the pigment so formed is subsequently 

 disposed of. 



A consideration of the facts set forth in this chapter should 

 leave one in no doubt regarding the essential similarity between 

 the menstrual cycle in the Primates, and the cestrous cycle in 

 the lower Mammaha. Those who have denied that there is any 

 correspondence between " heat " and menstruation ^ have laid 

 stress upon the assertion that whereas " heat " in the lower 

 animals is the time for coition, this act, as a general rule, is not 

 performed during menstruation. But, as was first pointed out 

 by Heape, it is the procestrum alone and not the entire " heat 

 period " (a term used generally to include both procestrum and 

 oestrus) which is the physiological homologue of menstruation ; 

 and, moreover, the latter process in many of the Primates is 

 succeeded by a regular post-menstrual oestrus. 



The physiological identity of the procestrum with menstrua- 

 tion should always be kept in view in considering the cause and 

 nature of the phenomena, since, as will be seen later, many 

 strange errors have been committed, and wrong conclusions 



1 Kazzander, loc. cit. 



^ Assheton, " The Morphology of the Ungulate Placenta," Phil. Trams. 

 B., vol. cxoviii., 1906. 



^ Beard, in The Span of Oeatation and the Cause of Birth (Jena, 1897), 

 says, " very little is required in disproof " of this correspondence. 



