84 THE PHYSIOLOGY OF REPRODUCTION 



pregnant period in the bitch (see below, p. 98). In this connection 

 it is interesting to note that, according to Hitschmann and Adler, 1 

 the pre-menstrual uterus in man undergoes changes which are 

 similar in character to those observed in the pregnant uterus. It 

 seems possible, therefore, to regard menstruation in man as 

 representing pseudo-pregnant destruction (see pp. 107 and 156) as 

 well as prooestrous degeneration, the two series of changes being 

 here telescoped into one month. 2 



The average length of the normal menstrual cycle, as already 

 mentioned, is twenty-eight days. Of these about five are occupied 

 by the pre-menstrual swelling, four by menstruation, and probably 

 about seven by the regeneration process, leaving not more than 

 twelve days for the period of quiescence. 3 There can be no doubt, 

 however, that the length of the respective stages must vary according 

 to the extent of the destruction and the amount of tissue which it 

 is necessary to replace. According to Westphalen, 4 the regenerative 

 process may last for as long as eighteen days, or until the commence- 

 ment of the succeeding pre-menstrual swelling. 5 



THE CYCLE IN MONKEYS 



The histology of the menstrual cycle in Semiiopithecus entellus 

 and Macacus rhesus has been very fully studied by Heape. 6 Pre- 

 viously to Heape's work, Bland Sutton 7 had paid some attention to 

 the histology of the menstrual process in Macacus rhesiis, but without 

 entering into great detail. More recently van Herwerden 8 has 

 given an account of the cyclical changes of the uterus in Cercocebus 

 cynomolgus. 



Heape has divided the cycle into the following four periods and 

 eight stages : 



1 Hitschmann and Adler, "Der Bau der Uterusschleimhaut des Geschlechts- 

 reifen Weibes," Nonatschr. f. Geb. u. Gyncik., vol. xxvii., 1908. 



2 Marshall and Hainan, "On the Post-CEstrous Changes occurring in the 

 Generative Organs and Mammary Glands of the Non-Pregnant Dog," Proc. 

 Roy. Soc., B., vol. Ixxxix., 1917. 



3 Whitridge Williams, loc. tit. 



4 Westphalen, loc. tit. 



5 For further references to the subject of menstruation in the human 

 female the following authors may be consulted : Steinhaus, Menstruation 

 and Ovulation, Leipzig, 1890 ; Heape, Phil. Trans., B., vols. clxxxv. and 

 clxxxviii., 1894 and 1897 ; Gebhard, " Die Menstruation," Veifs Handbtu-h 

 der Gyndk., vol. iii., 1898. For an account of the various pathological changes 

 which are known to occur in the human uterus, see Macgregor, A Contribution 

 to the Pathology of the Endometrium, Edinburgh, 1905. 



6 Heape, loc. tit. 



7 Bland Sutton, "Menstruation in Monkeys," Brit, Gynvec. Jour., vol. ii., 

 1880. 



8 Van Herwerden, " Bijdrage tot de Kennis van den Menstrueelen Cyclus," 

 Tijdschrift. d. Ned. Dierk. Vereen., vol. x., 1906. 



