2O6 RAYMOND PEARL AND H. M. PARSHLEY. 



cow. (3) Age of cow. (4) Date of service. (5) Date of birth 

 of calf. (6) Sex of calf. (7) Weight of calf. (8) "If you know 

 positively, state whether the cow was served in the first, middle, 

 or last part of heat." Space was provided on each blank for 

 recording a year's breeding operations. These schedules were 

 widely distributed among the leading stock breeders of the state, 

 and the inquiry extended over a period of about four years. As 

 in all such studies a portion of the blanks returned were defective 

 and not usable, either through failure to fill in essential points 

 or from mistakes. One of the commonest defects arose from the 

 fact that the bull was allowed to run in the pasture with the 

 cows, thus precluding any possibility of accurate knowledge of 

 the period of oestrus at which coitus occurred. On the other 

 hand the great majority of the returns were filled up in a very 

 careful and painstaking manner, and furnish valuable data on a 

 number of problems in the physiology of breeding which are 

 much more in the foreground of biological interest at the present 

 time than they were when the inquiry was instituted. 



All of the breeds of cattle at all common in the eastern United 

 States are represented in the returns. The majority are either 

 grade or cross-bred animals, but a fair proportion represent "pure 

 bred," registered stock, particularly in the case of the dairy 

 breeds. 



In the present paper only a single problem will be discussed. 

 In later communications it is hoped to take up certain other 

 problems in the physiology of breeding for which data are 

 available in these returns. The problem here considered may 

 be stated as follows: Is there any relation and if so of what sort, 

 between the time in period of oestrus at which coitus occurs and 

 the sex of the resulting offspring? This is obviously a matter of 

 much practical as well as theoretical importance. There is 

 perhaps no one thing that would be of more vital importance to 

 the stock-breeder than to be able to control, in some degree even, 

 the sex of the animals which he breeds. 



The visible manifestations and the duration of oestrus in the 

 cow are rather variable matters. In the older literature, and 

 in the minds of most practical breeders at the present time, no 

 precise distinction is made between the two divisions of the 



