THE EVOLUTION OF THE PLACENTA. 737 



with this conclusion the form of the placenta completely tallies. 

 The primitive Edentata and Ungulata had no doubt a diffused 

 placenta which was probably not very different from that of the 

 primitive Lemurs ; but how far these groups arose quite in- 

 dependently from the primitive stock, or whether they may have 

 had a nearer common ancestor, cannot be decided from the 

 structure of the placenta. The Carnivora were certainly an 

 offshoot from the primitive placental type which was quite in- 

 dependent of the three groups just mentioned ; but the character 

 of the placenta of the Carnivora does not indicate at what stage 

 in the evolution of the placental Mammalia a primitive type of 

 Carnivora was first differentiated. 



No important light is thrown by the placenta on the affinities 

 of the Proboscidea, the Cetacea, or the Sirenia ; but the character 

 of the placenta in the latter group favours the view of their being 

 related to the Ungulata. 



