THE CESTROUS CYCLE IN THE MAMMALIA 41 



With many foreign breeds lambs are born twice yearly. Thus 

 Dr. Annandale informs me that the horned sheep which run half 

 wild in Patani, in the Malay Peninsula, normally have lambs twice 

 a year. It would appear also that among the indigenous sheep of 

 India, which are scarcely ever supplied with any artificial or other 

 food, green or dry, beyond what they can pick up at the pasture 

 ground, lambs may be born three times in two years, and that there 

 are no definite seasons for lambing. 1 



Among the Merino sheep in Cape Colony the sexual season is 

 April (the autumn month, corresponding to October in this country), 

 but some sheep come " in season " earlier. At high altitudes, 

 however, where the sheep subsist entirely upon the natural produce 

 of the veldt, the sexual season is May, or a month later than the 

 usual time in Cape Colony. On the other hand, in the low country 

 below the second range of mountains, there are two seasons for 

 " tupping," and lambs are produced twice a year. Among the 

 Merinos in Argentina there are also two breeding seasons within the 

 year. 



Probably the maximum amount of sexual activity experienced by 

 any sheep is that reached by certain Australian Merinos which are 

 described as being able to breed all the year round, a fact which 

 implies, in the absence of gestation, an unbroken series of dioestrous 

 cycles. The report of the Chief Inspector of Stock for New South 

 Wales divides the time of lambing into six periods which embrace 

 the entire year. 2 



That the great variability in sexual activity which, the sheep 

 exhibits is dependent largely upon differences in food supply and 

 climate cannot be doubted, for the Blackfaced sheep in Scotland 

 and the Merinos in Cape Colony afford direct evidence that this is 

 the case. Indeed, the effect of the environment on the recurrence of 

 breeding was noted long ago by Aristotle, 3 who observes that " in 

 some places where the weather is warm and fine, and food is 

 abundant," sheep may have lambs twice a year. The result of 

 flushing (or the practice of stimulating the generative system by 

 supplying extra food or better pasture, and thereby hastening the 

 approach of the sexual season and increasing the fertility) is further 

 evidence of the effect of good nourishment upon the sexual and 

 reproductive powers. On the other hand, there can be no question 

 that the varying degrees of breeding activity are in part racial 



1 Shortt, .1 Manual of Indian Cattle and Sheep, 3rd Edition, Madras, 1889. 



2 Wallace (K.), Farming Industries of Cape Colony, London, 1876 ; The Rural 

 Economy and Agriculture of Australia and New Zealand, London, 1891 ; 

 Argentine Shows and Live Stock, Edinburgh, 1904. 



3 Aristotle, History of Animals (Cresswell's Translation), Bonn's Library, 

 London, 1862. Oxford Edition (Thompson's), 1910. 



