SEX RATIOS IN FO2TAL CATTLE. 269 



births and dizygotic twins in the Short Horns included 870 males 

 and 889 females with a sex ratio of 97.86. The corresponding 

 group in the Holstein-Friesians contains 976 males and 996 

 females with a sex ratio of 97.99. 



In the Short Horns the total including the twins of the same 

 sex, a very few of which might have been monozygotic, there are 

 874 males and 893 females, the ratio being 97.87. The corre- 

 sponding group of Holstein-Friesians contains 1,006 males and 

 1,030 females with a sex ratio of 97.66. 



The total in both breeds was 1,880 males and 1,923 females, 

 making a total population of 3,803 with a sex ratio of 97.76. 



Thus it will be seen that there is no marked variation in the 

 sex ratios of the two breeds, the two in fact approximating each 

 other very closely. 



It is possible that in a mixed population there might be a 

 change in the sex ratio as has been indicated by various inves- 

 tigators in data on hybridization. Guyer ('09) found a great 

 excess of males among hybrid pigeons and suggested that "more 

 or less default in the metabolic processes because of the incom- 

 patibilities which must necessarily exist between two germplasms. 

 so dissimilar" would lead to a production of more males. 



M. Pearl and R. Pearl ('08), in comparing pure with cross 

 matings for man in Buenos Ayres, showed a "significantly 

 greater proportionate production of males in the offspring from 

 matings involving different racial stocks than in the offspring 

 from matings in which both parents belong to the same racial 

 stock." 



Unusual sex ratios might result in hybridization of breeds of 

 cattle that were unlike in respect to the size of the foetus. An 

 extreme case illustrative of this would be the bison-cattle crosses. 

 Babcock and Clausen point out that practically all of the off- 

 spring of this cross are females due to the increased size of the 

 hybrid foetus and the consequent abortion or death of the male 

 foetuses. Thus, sex eliminating factors, as in this case, would 

 change the secondary sex ratio. 



Wilckens found that in the " Niederungsrassen " the sex ratio 

 was 114 in 3,009 individuals as compared with an average ratio 

 of 107.3. 



