PEKIOD OF GESTATION. 4Q9 



Earl Spencer was inclined to believe that his ob- 

 servations show that " there is some foundation for 

 this opinion. . . . 



" In order fairly to try this," he says, " the cows 

 calved before the 260th day and those who calved 

 after the 300th ought to be omitted as being anoma- 

 lous cases, as well as the cases in which twins were 

 produced ; and it will then appear that, from the 

 cows whose period of gestation did not exceed 286 

 days, the number of cow-calves produced was 233 

 and the number of bull-calves 234 ; while, from those 

 whose period exceeded 286 days, the number of cow- 

 calves was only 90, while the number of bull-calves 

 was 152." l 



He neglects, however, to notice that in the entire 

 number of births, omitting the twins, there were but 

 340 cow-calves to 401 bull-calves, or a large prepon- 

 derance of males ; and that all the calves born after 

 the 300th day were females, while of those born be- 

 fore the 260th day ten were cow-calves and fifteen 

 bull-calves. 



M. Magne, on the contrary, found the period of 

 gestation longer with ewe-lambs than with ram-lambs, 

 and this he attributes to the greater development of 

 the males previous to birth. 3 



The duration of gestation seems to depend also to 

 some extent upon heredity. " It was ascertained by 

 the late Earl Spencer that of seventy-five cows in calf 

 by a particular bull, the average period was 288-J days 

 instead of 280, none of them having gone less than 



1 Journal of the Royal Agricultural Society, vol. i., p. 168. 



2 " Encyclopedic pratique de PAgriculteur," tome x., p. 485. 



