96 THE PHYSIOLOGY OF REPRODUCTION 



should be noted, however, that Button's investigation was upon 

 monkeys in this country, whereas Heape's observations relate to 

 Indian animals, and that in Pocock's experience, 1 menstruation 

 does not, as a rule, occur in Macacus rhesus in the Zoological 

 Gardens. But it would appear also from this author's observa- 

 tions that the severity of the menstrual process in monkeys may 

 vary within as wide limits as it is said to do in the human female. 



The changes which occur throughout the menstrual cycle in 

 Cercocebus cynomolgus have been studied in some detail by 

 van Herwerden, 2 who begins by classifying the material in two 

 groups. In group A are included those animals in which, at the 

 time of killing, the uterus was relatively small and menstrua- 

 tion was correspondingly slight. In group B are placed those 

 monkeys which, on being killed, showed comparatively large 

 well-developed uteri, and in which the menstrual process was 

 characterised by some degree of severity. Van Herwerden is of 

 opinion that the individuals included in the first category were 

 animals killed during the non-breeding season, while those be- 

 longing to group B were specimens killed at the breeding season, 

 when the generative organs were in a state of greater activity. 



The complete menstrual cycle in Cercocebus is divided into 

 the following periods and stages : 



I. Inter-menstrual period. 



f 1. Increase of superficial stroma elements. 

 II. Pre-menstrual period . Q1 . ,, . . 



v2. Slight swelling of mucosa. 



1. Increasing hypersemia. 



2. Rupture of capillaries. 



3. Formation of lacunae. 



TTT , , 4. Degeneration of epithelium and stroma 



III. Menstrual period . 



elements. 



5. Rupture of lacunre and tearing off of 



degenerate tissue. 

 . Beginning of regeneration. 



IV. Post-menstrual period. 



It will be seen from this scheme of classification that the 

 changes recorded by van Herwerden as occurring in the 

 menstrual cycle of Cercocebus are very similar to those described 



1 Pocock, "Notes upon Menstruation," &c., Proc. Zool. Soc., 1906. 



2 Van Herwerden, loc. cit. 



