GENETIC STUDIES IN POULTRY. 235 



other studies have indicated a ratio of less than fifty per cent, 

 males, both for living chicks and dead embryos. No reason for 

 this higher sex ratio is apparent. It is true that a number of 

 the birds were lost due to various causes but the writers have no 

 reason to believe that there was a selective mortality of the chicks 

 that were lost. 



The proportion of males among the embryos dying between 

 the twelfth day and eighteenth day of incubation is rather high, 

 being 55.82. However, if reference is made to Table IV. it may 

 be seen that it does not hold consistently true that the males 

 exceed the females in the D 3 class. In the DS class there is 

 practically an equality of males and females, the ratio of males 

 being 50.06. All previous investigators reporting on the prenatal 

 sex ratio alone in birds have reported a sex ratio less than fifty 

 per cent. They likewise have seemed agreed that a selective 

 mortality of one sex or the other previous to hatching does not 

 occur. 



The number of birds upon which the correlations have been 

 calculated is small but the results found here are in general 

 agreement with those of other investigators. More of the birds 

 were not inc'uded in these studies because the mean egg weight 

 varies for different breeds and in most cases the antecedent egg 

 product on on the birds used in the various crosses was not known. 



SUMMARY. 



1. The sex ratio for 2,910 chicks and embryos examined was 



5I-I3- 



2. The sex ratio for total living chicks was 50.97, for embryos 



dying between the eighteenth and twenty-first days of incubation 

 50.06, and for embryos dying between the twelfth and eighteenth 

 days 55.82 per cent. 



3. No tendency for an increase or a decrease in the sex ratio as 

 the hatching season progressed was noted. 



4. The sex ratio of hybrid birds is approximately the same 

 as for that of the pure breeds observed. 



5. No relationship between the sex ratio and the factors of 

 mean individual egg weight, antecedent egg production, and 

 actual egg production during the hatching season is apparent. 



