THE CESTROUS CYCLE IN THE MAMMALIA 57 



Monkeys. The essential similarity between the procestrum in the 

 lower Mammalia and menstruation in monkeys will be made clear in 

 the next chapter, when the histological changes which occur in the 

 uterus are described. The consideration of the subject, however, is 

 somewhat complicated by the fact pointed out by Heape 1 that, 

 whereas monkeys may have a continuous series of dicestrous cycles 

 usually at regular monthly intervals, they are not necessarily capable 

 of breeding at every heat period. Thus there is evidence that in 

 the gorilla and chimpanzee in West Africa and in the orang-utan 

 of Borneo and the Eastern Archipelago there are special sexual 

 seasons, 2 and Heape 3 has shown that the same can be said of Semno- 

 pithccits entt'llus arid Macacus rhesus in India, but that the exact time 

 for breeding varies in the different localities. Thus in Simla Macacus 

 rhesus copulates about October, and gives birth to young about 

 August or September in the following year, whereas on the plains 

 around Muttra it seems probable that March is the usual month 

 when young are born. Kingston 4 states that in the Himalayas 

 the Rhesus monkeys pair in September and the young are born in 

 March. However, Mr. Sanyal, the Superintendent of the Zoological 

 Gardens in Calcutta, expressed the opinion that M. rhesus can breed 

 at all times of the year. 3 On the other hand, it has been shown by 

 van Herwerden 5 that Cercocebus in the island of Banha breeds only, 

 as a rule, in the late summer or early autumn. 



Heape 6 states that with the Macacus in the .Gardens in London 

 there is definite oestrus which always occurs after the cessation of the 

 menstrual discharge, and persists for two or three days, and Ellis 7 

 has shown that this is also probably the case with the orang-utan 

 as well as with various monkeys. 



Pocock 8 has given some interesting details concerning the 

 phenomena which attend the menstrual process in various monkeys 

 and baboons in the Zoological Society's Gardens. He states that the 

 females of many species at about the time of menstruation exhibit 

 extreme congestion of the naked area surrounding the genital and 



1 Heape, loc. cit. 



- Win wood Reade, Savage Africa, London. Molirike, Das Ausland, 1872. 

 Garner, Gorillas and Chimpanzees, 1896. Burton (Trips to Gorilla Land, vol. i., 

 London, 1876) says that the gorilla breeds about December, a cool, dry month, 

 and that the period of gestation is five to six months. 



3 Heape, "The Menstruation of Semnopithecus entellus," Phil. Trans., B., 

 vol. clxxxv., 1894, "The Menstruation and Ovulation of Macacus rhesus," 

 Phil. Trans., B., vol. clxxxviii., 1897. 



4 Kingston, .1 Xaturalist in Himalaya, London, 1920. 



5 Van Herwerden, loc. cit. 



6 Heape, The Sexual Season, etc. 



7 Havelock Ellis, Psychology of Sex, vol. ii., Philadelphia, 1900. 



8 Pocock, " Notes upon Menstruation, Gestation, and Parturition of some 

 Monkeys that have lived in the Society's Gardens," Proc. Zool. Soc., 1906. 



