PEEIODS OF GESTATION. 



435 



has villi studded over it except at the poles, where small areas 

 are devoid of them. 



All mammals except the Monotremes and Marsupials have a 

 placenta in one of these five forms. 



The length of gestation in farm animals has been divided by 

 Gurlt into seven periods. The last period and the dimensions 

 of the embryo are given in the table below : — 



The weight of the fcetus of the mare at birth varies according 

 to breed. The lowest, in the Corsican mare, is 35 lb. ; in a 

 Suffolk -Boulonnaise mare, Chauveau mentions 135 lb. The 

 weight of a calf at birth is about 2 '31 parts of the cow, a 

 lamb 10 to 11 lb., a pig 5 lb., and a chick \\ ounce. 



