27O F. M. JEWELL. 



3. Errors in Sampling. It is also probable that errors might 

 be made in sampling in the secondary and tertiary sex ratios. 

 This might be done quite unconsciously by farmers, due to failure 

 to record the sex promptly at birth. Some farmers might be 

 prejudiced in favor of one sex and if the calves of the other sex 

 should die before registration they probably would not be entered. 



From this viewpoint one might compare the discrepancies in 

 data on the sex ratios in cattle as given by various investigators, 

 ranging from 97.76 (in Table IV. above) to 107.2 in the data of 

 Wilckens and 113.3 as given by Pearl and Parshley. 



Numbers Involved. The question might be raised as to whether 

 the number of foetuses, 1,000, would represent a small enough 

 number to make a material difference in the sex ratio as compared 

 with a much larger number. Considering the sex ratio in the 

 larger groups of foetuses when grouped according to length it 

 would appear that the sex ratio for the total collection, 123.21, 

 is very near to the true one during foetal development in cattle. 



B. Association oj Sexes in Fcetal Twins. 



The data indicates that the sex ratio of 134 for dizygotic, 

 foetal twins, as found by Dr. F. R. Lillie, is not far from the 

 normal of the population and therefore the association of sexes 

 in twins is presumably a random sampling. 



CONCLUSIONS. 



1. The sex ratio during fcetal development in cattle is 123.21 



2. This sex ratio of 123.21 during fcetal development compared 

 with the much lower sex ratios at birth indicates a greater mor- 

 tality of males during intrauterine development. 



3. When compared with the sex ratio of 123.21 the sex ratio 

 of 134 in F. R. Lillie's collection of twins in fcetal cattle does not 

 indicate any interference with the chance assortment of sexes in 

 dizygotic twinning in cattle. 



4. The data do not indicate that there is any particular stage 

 in development during which there is a more marked mortality 

 among the males than in any other stage. 



5. There is no indication that the breed causes any variation 

 in the sex ratio. 



