268 



F. M. JEWELL. 



If we can compare the data obtained during foetal development 

 with that given above as the ratio at birth, it will be noticed 

 that the former on the whole, with a sex ratio of 123.21, is well 

 above the secondary ratio. Since in all of these cases the data 

 include various breeds, it is fair to compare them in this respect. 

 It would thus appear that there is a greater mortality among 

 the male foetuses, for only in this way would the sex ratio at 

 birth be less than that during fcetal development. The figures 

 as they stand in the present article, however, do not show suffi- 

 ciently well-marked evidence to support the supposition that 

 there is a greater mortality among the males at any particular 

 stage of development. 



2. Possible Variations in Different Populations or Breeds 

 During the summer of 1919 correspondence was carried on with 

 a large number of breeders to obtain data for comparison of the 

 sex ratio at birth with the ratio during fcetal development, and 

 also to determine the influence, if any, of the breed on the sex 

 ratio. The Short Horn was taken as the beef type and the 

 Holstein-Friesian as the dairy type of cattle. Only registered 

 cattle were used and the data included the sire's name and 

 number, the year, and the number of male and female calves by 

 that sire. The total results of this investigation are given in 

 Table IV. Data were also obtained in reference to twins of the 

 same sex and of opposite sexes. 



TABLE IV. 



SHOWING THE SEX RATIOS FOR SHORT HORNS AND HOLSTEIN-FRIESIANS. 



From this table it will be seen that the total number of single 



