GESTATION AND LACTATION 69 



third month. If the complete natural outline of the virgin 

 womb cannot be made out, careful examination should 

 always be made on the right and left side for the enlarged 

 horn and its living contents. Should there still be diffi- 

 culty, the mare should be placed on an inclined plane, 

 with her hind parts lowest, and two assistants, standing on 

 opposite sides of the body, should raise the lower part of 

 the abdomen by a sheet passed beneath it. Finally the ear 

 or stethoscope applied on the wall of the abdomen in front 

 of the stifle may detect the beating of the foetal heart (one 

 hundred and twenty-five per minute) and a blowing sound 

 (the uterine sough), much less rapid and corresponding to 

 the number of the pulse of the dam. It is heard most 

 satisfactorily after the sixth or eighth month and in the 

 absence of active rumbling of the bowels of the dam." 



66. The period of gestation. The period of develop- 

 ment from the fertilization of the egg by the sperm-cell 

 until the birth of the fully developed offspring capable 

 of independent existence outside the body of the mother 

 is known as the period of gestation. Among oviparous 

 animals it is the period of incubation. This period varies 

 greatly as between different species, but under normal 

 conditions is fairly uniform in animals belonging to the 

 same species. The normal period of gestation has in 

 general a more or less definite relation to the size of the 

 animal. The length of gestation in animals as reported 

 by various authors : is as follows : 



1 Nathusius, "Zool. Garten Jahrg.," 3, 1862. 



Heape, "The Sexual Season," Quarterly Journal of Micro- 

 scopical Science, vol. 44, 1900. 



Ewart, "The Development of the Horse," Quarterly Journal 

 of Microscopical Science. 



Wortley Axe, "The Mare and the Foal," Journal of the Royal 

 Agricultural Society, 3d series, vol. IX, 1898. 



