PHYSIOLOGY. 3 1 



this situation, and development of the embryo now 

 commences. 



The time which must necessarily elapse between 

 the periods of impregnation and parturition has been 

 termed the period of gestation. 



The Period of Gestation. 



This period varies very much in different animals, 

 and also in the same class of animals when subjected 

 to different surroundings and treatment. 



In the Mare, the period of gestation is about 

 forty-eight weeks, but varies more in this animal 

 perhaps than in any other. Some brood mares foal 

 regularly at a little over ten months, while others are 

 pregnant nearly a year, and then give birth to a 

 healthy foal. 



Note.—M.r. John Renfrew, M.R.C.V.S., Glasgow, 

 has furnished me with the record of two cases, one, 

 that of a Pony Mare belonging to Mr. Mitchell, 

 Polmont, Scotland, which had been served for twelve 

 months and three days, and was then said to be in 

 season ; was sent to the stallion and served, and the 

 next day gave birth to a healthy colt foal. 



The other case was that of a thoroughbred Mare, 

 the property of Mr. Stevenson, Hurlet, Scotland, 

 which carried her foal twelve and a half months 

 regularly. 



As a rule, a Mare carrying a colt-foal (horse-colt) 

 is pregnant several daysolonger than with a filly-foal 

 (mare-colt). If the animal be kept at gentle work, it 

 will generally give birth several days earlier, and 



