SEX RATIOS IN FCETAL CATTLE. 



TABLE III. 



265 



SHOWING A COMPARISON OF THE SEX RATIOS OF RELATIVELY YOUNGER AND 



OLDER FCETUSES. 



20-100 cm. the sex ratio is 120.34. The objection may be 

 raised, and quite rightly, that 112 is too small a number on 

 which to base definitely the sex ratio for individuals from 0-20 

 cm., especially since, when the next group of individuals from 

 20-30 cm. is included, the sex ratio from 0-30 cm. becomes 

 lowered to 120.0. However, it should be pointed out that in 

 the 20-30 cm. group, there is a relatively low sex ratio of 102 

 when compared with the total of 123, and that this is probably 

 due to chance. When this is taken with the sex ratio of the 

 0-20 cm. group with a sex ratio of 148, it of course lowers it 

 considerably and the reverse is true for the individuals above 

 that length. Thus, the groups from 30-100 cm., being relieved 

 of the burden of the 20-30 cm. group, have a combined sex 

 ratio of 124.39. This no doubt partly explains such discrepancies 

 as appear in passing from the 0-20 cm. to the 20-30 cm. groups, 

 and in the 20-100 cm. and the 30-100 cm. groups. If the 20-30 

 cm. group had been such that it could have been considered 

 practically normal, the wide and suddenly marked differences 

 here shown probably would not exist. 



However, it might be suggested that, although the sudden drop 

 in the number of males in the 20-30 cm. group may represent a 

 chance occurrence, it might be that this is the critical period in 

 embryonic development in which there is a greater viability in 

 the female foetuses and that the normal sex ratio for this group 

 might well be below the average of 123. 



In the 0-40 cm. group the sex ratio of 125.96 shows a greater 



