26O F. M. JEWELL. 



Wilckens ('87) gives the ratio in cattle at or near the time of 

 birth as 107.3, the number of individuals being 4,900. Pearl 

 and Parshley ('13) in their studies on the sex ratio in cattle in 

 relation to coitus and the period of oestrus give the ratio as 1 13.3 

 in a total population of 480. In more recent data by Pearl ('17) 

 covering 1,313 individuals the sex ratio was 100.12. 



It should be pointed out that in other animals-the data shows 

 that there is no correlation between the sex ratio and multiple 

 births. Parker and Bullard ('14) and also Wentworth ('14) 

 have shown this to be true for pigs; King and Stotensburg ('15) 

 for rats, and Newcomb ('04) showed that in man the sex ratio 

 in twins was practically the same as in single births. 



It should be understood that a different rate of mortality in 

 the sexes either during intrauterine development or after birth 

 would cause the sex ratio to vary at different ages, and for this 

 reason the sex ratio is usually spoken of as primary, secondary 

 and tertiary. The primary is the ratio determined at conception 

 and is the original sex ratio; the secondary is that at time of 

 birth and the tertiary during adult life. 



A. M. Schultz ('18) attempted to determine the primary sex 

 ratio for man in an indirect way from the data on the mortality 

 of embryos and foetuses combined with the sex ratio at birth. 

 In doing this he stated that only in case the mortality of the two 

 sexes was equal would the primary and the secondary .sex ratios 

 be equal ; that if the male and female abortions were absolutely 

 equal, the sex ratio would be smaller at conception than the 

 secondary, and that if there were a greater intrauerine mortality 

 for males than for females, then the primary sex ratio would be 

 greater than the secondary in proportion to the number of 

 abortions and stillbirths. 



In order to determine the primary sex ratio, he ascertained the 

 sex ratio in abortions and stillbirths, and the number of such 

 cases for every 100 living born, both male and female. From 

 the data as given by various writers and from the material that 

 he used (nearly 600 foetuses of the embryology department of 

 Carnegie Institution) he established the following probable 

 values : 



