40 THE PHYSIOLOGY OF REPRODUCTION 



the locality or climate. Thus with 0. vignei in the Punjab, the sheep 

 begin to breed in September, whereas, with the same species in Astor, 

 the sexual season must be considerably later, since the young in the 

 latter district are produced about the beginning of June.^ 



Scotch Blacktaced sheep in the Highlands experience two 

 dioestrous cycles, each of three weeks' duration, so that the annual 

 sexual season for these animals lasts six weeks. In the Lowlands 

 the sheep of this breed may have at least three recurrent dicestrous 

 cycles in , the absence of the ram, while flpekmasters inform me 

 that, under unusually favourable conditions, there may be as 

 many as five or six, the duration of each cycle varying from 

 about thirteen to eighteen days. It can hardly be doubted that 

 of the two conditions of the Scotch Blackfaced sheep that of the 

 Highland ewes is the more natural, for sheep, in their wild state, are 

 essentially mountain animals, being almost entirely confined to 

 mountain districts in the Holarctic region, their range only just 

 extending across the bordfer into the far warmer Oriental region. 

 " The immense mountain ranges of Central Asia, -the Pamir, and 

 Thian-Shan of Turkestan may be looked upon as the centre of 

 their habitat." ^ 



The sexual sefason in hill sheep in Great Britain is ordinarily 

 from about the middle of November until the end of the year. 

 Under exceptional circumstances individiials may experience oestrus 

 at other seasons, such as in April after an early abortion in the 

 winter. In other British breeds the sexual season is earlier. Thus 

 Hampshire Down sheep are often "tupped" in the summer, but 

 they do not, as a rule, breed more than once a year. The Limestone 

 sheep of Westmorland and Derbyshire, and the Dorset Horn sheep 

 of the South of England, are the only British sheep which are 

 ordinarily capable of breeding more than once annually. With the 

 former the general lambing season is from the middle of February to 

 the middle of March, but lambs are often born earlier. The ewes 

 sometimes receive the -ram very early when suckling the lambs, so 

 that a second crop of lambs is born in August. This increase in the 

 sexual capacity is especially noteworthy in view of the fact that 

 Limestone sheep are classed as a mountain breed which thrives best 

 on dry heaths or bare hill pastures. In Dorset Horn sheep lambs 

 are frequently produced twice a year, but the practice is discouraged 

 as it is said to deteriorate the ewes. With this breed oestrus may 

 continue to recur (in the absence of the ram) from the summer 

 sexual season (when the sheep are tupped) onwards until the late 

 autumn or even longer. 



1 Lydekker, loc. cit. 



2 Flower and Lydekker, Matninals Living and Extinct, London, 1891. 



