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-raenstrual 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 150) as 

 well as prooestrous degeneration, the two series of changes being 

 here telescoped into one month.- 



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 AVestphalen, 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 Xnmiojiif/irrn* rnt?llii* 

 and Mai-aril* /-/u'.s/'.s has been very fully studied by Heape." Pre- 

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

 the histology of the menstrual process in Ma<-cn* /-A <*//*, but without 

 entering into great detail. More recently van Herwerden s has 

 given an account of the cyclical changes of the uterus in Crri-occlu* 

 cynomolgus, 



Heape has divided the cycle into the following four periods and 

 eight stages : 



1 Hitschmann and Adler, "J)er Bander Cterusschleimhaut des Geschlechts- 

 reifen Weibes," J/o/'"^v/,/-. /'. <!,'!,. ,/. f/,//////-., vol. xxvii., 1908. 



2 Marshall and Hainan, "On tlie ]'ost-<Kstrous Changes occurring in the 

 (Generative Organs and Mammary < {lands of the Non-Pregnant Dog," J'n: 

 /A*//. No,., B., vol. Ixxxix., 1!)17. 



! Whitridge Williams, (<>c. <-it. 



4 Westphalen, /<. fit. 



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

 female the following authors may be consulted : Strinhaus, Mi>iixti-nnti<,ii 

 ni,,l < h-nlntiun, Leip/.i^, |*90; Heape, /V//V. '/'/"/'.<., B., vols. clxxxv. and 

 dxxxviii., 1K94 and 1897; (Jebhard, "Die Menstruation," IV//'.< llnndlmrh 

 '/?/ d\tf /x'r/.-., \nl. iii., 1898. For an account of the various pathological changes 

 which are known to occur in the human uterus, see Macgregor, .1 Contribution 

 to the Pathology of th>' Emiomi'triii.m, Edinburgh, 1905. 



6 Heape, loc. cit. 



7 Bland Sutton, "Menstruation in Monkeys," Brit. <!<in<\ .l<>nr., vol. ii., 

 1880. 



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

 Tij<lschrift. d. X<->l. l)i< i-(-. \'eree/>., vol. x., 1906. 



