HEREDITY AND SEX 193 



ments of others. In ordinary breeding operations on the 

 range, the bull invariably runs with the cows and breed- 

 ing occurs during the first part of the heat. If the sex 

 is determined to any extent by the particular stage of 

 heat, then in this case the offspring should be largely 

 female. But such is not the case, the proportion of the 

 sexes is practically equal, subject to seasonal or other 

 variations not entirely explainable. Thury's results 

 have not been satisfactorily confirmed. Miles 1 recorded 

 the proportion of sexes among cattle and sheep on the 

 Michigan Agricultural College farm for a period of ten 

 years. The results were as follows: Sheep, 102.5 males 

 to 100 females. Cattle, 118.4 males to 100 females. All 

 the animals were bred during the first part of the heat 

 and the offspring should have been more largely female. 

 The proportion of the sexes seems to be subject to wide 

 variation, and therefore any investigations of this kind 

 must necessarily include large numbers of animals and 

 the observation be carried over a series of years to make 

 the results of any value. 



184. Seasonal variations in proportion of sexes. 

 The proportion of the sexes is subject to wide variations 

 apparently due to seasonal influences. Quoting again 

 from Miles : 2 



" In 1864 and 1865 the bull-calves were 2.5 to 1 heifer ; 

 in 1866 and 1867 the heifers were considerably in excess ; 

 in 1868 and 1869 the heifers were nearly 2 to 1 bulls ; in 



1870 the bulls were decidedly more numerous ; and in 



1871 and 1872 there were more than 2 bulls to 1 heifer. 

 In 1872 there were 2 rams to 1 ewe, and the bulls were 

 nearly in the same proportion to the heifers, which would 



1 Miles, " Stock Breeding," 1878, p. 265. 



2 Ibid., p. 299. 

 o 



