THE RABBIT AS A TYPE OF MAMMALS. 657 



While Sir William Turner, " the grand master of placental 

 research," in his arrangement of placentas, allots the lowest 

 place to such diffuse forms as that of the pig, passes thence 

 to the cotyledonary of Ruminants, thence to the zonary 

 of Carnivores, and finally to the discoidal of monkeys and 

 man, others maintain that the discoidal, as illustrated in the 

 Insectivora, is the most primitive type. 



To avoid confusion it may be better, as Hubrecht sug- 

 gests, to revert to the old terms caducous and non-caducous, 

 instead of deciduate and indeciduate, for all placental mam- 

 mals have a " decidua," i.e., a specially active region of the 



FIG. 229. View of Embryo with its foetal membranes. 

 (After KENNEL.) 



am., Amnion ; d., dwindled yolk sac ; al. t allantois ; a/.i, sub- 

 zonal membrane ; z., villi. 



mucous membrane of the uterus to which the embryo is 

 attached. Moreover, the distinction between deciduate and 

 indeciduate is one of degree, for no sharp line can be 

 drawn between the two types. 



THE RABBIT as a type of Mammals. 



The rabbit (Lepus cuniculus) is a familiar representative of 

 the Rodent order, to which rats and mice, voles and beavers, 

 42 



