THE (ESTROUS CYCLE IN THE MAMMALIA 65 



processes of menstruation and ovulation is discussed in a later 

 chapter. 



Little is definitely known concerning the length of the 

 gestation period in the various apes and monkeys. Pocock's 

 observations show that in Macacus nemestrinus this period is 

 between six and seven months. Blandford l states his belief that 

 about seven months is the usual period for the genus Macacus. 

 Sanyal, according to information recorded by Sclater, 2 found 

 that a female of Cercopithecus cynosurus in the Zoological 

 Gardens, Calcutta, carried her young for seven months. 



Gestation in the Quadrumana is dealt with at some length 

 by Breschet, 3 who cites many of the older observations. He 

 shows that the question as to the duration of the period is com- 

 plicated by the fact that monkeys, unlike the majority of 

 Mammals, may copulate at other times than the breeding 

 season, and that they are said occasionally to experience men- 

 struation during pregnancy. 



Man. As is well known, menstruation recurs normally in the 

 non-pregnant human female at intervals of from twenty-eight to 

 thirty days. The exceptions to this general rule are, however, 

 very numerous, and have often been noticed. Thus the interval 

 may be extended to five weeks, or be abbreviated to two weeks 

 without any derangement to the general health. " In one 

 hundred women, sixty-one [were found] to menstruate every 

 month, twenty-eight every three weeks, ten at uncertain in- 

 tervals, and one, a healthy woman aged twenty-three years, 

 every fortnight/' 4 The duration and amount of the discharge 

 may also vary considerably both in different women and in 

 the same woman at different times. 



It is stated, also, that the periodicity of menstruation depends 

 partly on the climatic conditions, and that women in Lapland 



1 Blandford, The Fauna of British India, vol. i., London, 1888. 



2 Sclater, Mammals of South Africa, London. 



3 Breschet, " Recherches anatomiques et physiologiques sur la Gestation 

 des Quadrumanes," Memoires de I'Acad. des Sciences, vol. xix. , 1845. 



4 Laycock, loc. cit., and Havelock Ellis, loc. cit. There is in some cases a 

 tendency for the cycle to become divided up into two cycles, separated by 

 the so-called " Mittelschmerz," or inter- menstrual pain, which is occasion- 

 ally accompanied by a sanguineous discharge. (Halliday Croom, "Mittel- 

 schmerz," Trans. Edin. Obstet. Soc., vol. xxi., 1896). 



E 



