SEX DETERMINATION IN CATTLE. 225 



time of service in the oestrous period and the sex of the subsequent 

 offspring in domestic cattle are subjected to biometric analysis. 

 These statistics are much more extensive than any which have 

 hitherto been collected for the study of this problem in cattle. 

 It is shown: 



1. That as the time of coitus approaches the end of the cestrous 

 period there is a progressive increase in the proportion of male 

 young born. 



2. That in the extreme case this increase in the proportion of 

 male births is probably statistically significant and not to be 

 attributed to errors of random sampling. 



3. That these modifications of the sex ratio cannot be at- 

 tributed to age differences or to any other factor yet suggested. 



A possible explanation of the results and their practical 

 bearings are discussed. 



