2O8 RAYMOND PEARL AND H. M. PARSHLEY. 



between the returns and the true physiological division is prob- 

 ably substantially as follows: 



Time of Coitus as Recorded. Time of Coitus in Relation to 



Actual Stage in CEstrus of 

 Individual. 



"Early." Early -f- some in middle division. 



"Middle." Middle + some in early stage 



+ an equal number in late 

 stage. 



"Late." Late + some in middle division. 



Finally there seems no reason to think that a psychological 

 bias, conscious or unconscious, on the part of the breeders has 

 influenced the returns. The opinions of breeders in regard to 

 sex determination, so far as we have been able to get at them, 

 are as follows: The majority of cattle breeders attach no sig- 

 nificance to the time of service as a factor in influencing sex. 

 Either they have never heard of any theory regarding the matter, 

 or if they have are not disposed to attach any significance to it, 

 or to modify or regulate their breeding practice in any way to 

 conform to such a theory. A much smaller number of breeders 

 have a decided opinion on the matter, which they usually believe 

 to be supported in greater or less degree by their own experience. 

 This latter class falls into two groups, about equal in numbers, 

 and about equally dogmatic in their adherence to their particular 

 views. One group believes that in order to secure a preponder- 

 ance of females service must occur early in the "heat," whereas 

 the other group maintains that to reach this end service must be 

 late in the "heat." Thus one group offsets the other. Even 

 from the men in these classes, however, the returns bear every 

 evidence of being carefully and honestly made. An occasional 

 somewhat rueful comment may be pencilled on the blank w r hen 

 the writer's theory failed to "work," but further than this pre- 

 conceptions appear to have played no part. 



The material would appear, from the biometrical standpoint, 

 to be particularly favorable on the following accounts: 



I. The sampling is strictly random. The different breeds are 

 represented in substantially the proportions in which they 



