402 PRINCIPLES OF STOCK-BREEDING. 



The period of incubation is said to be shortened 

 when hens' and ducks' eggs are set under a turkey. 1 



The following statistics will indicate the variations 

 that are liable to occur in the period of gestation of 

 different animals. M. Tessier, who continued his ob- 

 servations for forty years, 3 has made the most valuable 

 collection of facts in relation to this subject, which 

 will be quoted under their appropriate heads. 



According to Youatt, the average period of ges- 

 tation in the mare is eleven months, but it may be 

 diminished five weeks or extended six weeks. 8 



Of 582 mares reported by M. Tessier, the shortest 

 period was 287 days, the longest 419, and the average 

 330 days. 4 



M. Gayot has recorded the period of gestation for 

 twenty-five mares, the shortest period being 324 days, 

 the longest 367 days, and a mean of 343 days. 6 



It will be noticed that the range of variation is 

 less in the cases observed by M. Gayot, while the 

 average period exceeds that of M. Tessier's observa- 

 tion thirteen days. Of 575 cows observed by M. 

 Tessier 



21 calved between the 240th and 270th days, the mean time 



being 259 days. 

 544 calved between the 270th and 299th days, the mean time 



being 282 days. 



1 "Farmer's Cyclopaedia," p. 662; Quarterly Journal of Agricult- 

 ure, vol. x., p. 287. 



8 Carpenter's " Human Physiology," p. 983. 



3 " The Horse," p. 222. 



4 Johnson's " Farmer's Cyclopaedia," p. 562 ; " Encyclopedic pra- 

 tique de 1'Agriculteur," vol. viii., p. 298. 



6 Ibid. 



