THE CESTROUS CYCLE IN THE MAMMALIA 45 



"Among captive animals, not more than two dioestrous cycles 

 have been observed in the gnu during one sexual season. Gazella 

 dorcas has two or three ; the giraffe about three ; while the eland, 

 nylghau, and water-buck have a series of diosstrous cycles, each 

 lasting three weeks, during May, June, and July each year. 



"The gayal and bison, the axis and wapiti deer, on the other 

 hand, experience a continuous series of dioestrous cycles all the year 

 round, at intervals of about three weeks." ^ 



Heape states also that with red-deer in the Zoological Gardens 

 there is a very extensive series of dioestrous cycles, and that with 

 wapiti deer in captivity the possibility of pregnancy at any season 

 is only prevented by the fact that the male does not rut during the 

 casting and growth of the antlers. 



The males of many of the other species referred to experience a 

 definite rutting season, like the stag in Britain. 



As already mentioned, the male camels in the Zoological Gardens 

 in London experience rut in early spring, or at the same time as 

 the sexual, season of the female camels in Mongolia.^ The period of 

 gestation in the camel is thirteen months, so that in this animal, 

 as in the walrus among carnivores, the recurrence of the sexual 

 season is delayed by pregnancy, and conception cannot take place 

 oftener than once in two years.^ The same is the case with the 

 wild yak in the deserts of Tibet,* and also, in all probability, with 

 the musk-ox in Greenland.^ 



The sexual season in many Ruminants is a period of intense 

 excitement, especially in those cases in which the males experience 

 a definite rut. (See above, p. 24, in Chapter I.) Thus, Catlin,* 

 referring to the American bisons, says : " The running season, which 

 is in August and September, is the time when they congregate into 

 such masses in some places as literally to blacken the prairies for 

 miles together. It is no uncommon thing at this season, at these 

 gatherings, to see several thoiisands in a mass, eddying and wheeling 

 about under a cloud of dust, which is raised by the bulls as they 

 are pawing in the dirt or engaged in desperate combats, as they 

 constantly are, plunging and butting at each other in the most 

 furious manner. In these scenes, the males are continually following 

 the females, and the whole mass are in a constant motion ; and all 

 bellowing (or ' roaring ') in deep and hollow sounds which, mingled 



1 Heape, loc. dt. 



2 According to Sven Hedin {Central Asia and Tibet, London, 1903) the wild 

 camels have a sexual season in December, January, and February, a fact which 

 suggests that they are polycestrous. • 



' Swayne, Seventeen Trips through SomalUand, London, 1895. 



* Prjewalsky, loo. cit. 



^ Lydekker, loc. dt. 



' Catlin, North American Indians, vol. i., 2nd Edition, London, 1841. 



