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placenta of a pig, and from which we may pass through the 

 Cheiroptera to the placenta of the other groups in which there 

 is at no time any raaternal tissue except the blood. In this case 

 we should probably continue to regard the Primates as a natural 

 group. On the other hand, paying attention to the primitive 

 characters of Erinaceus, we may regard the type of placentation 

 there found as the ancestral forrn from which the modifications 

 met with in the other groups of 'Deciduata' have been derived ; 

 and this may have as its corollary the separation not only of the 

 Lemurs from Tarsius, Monkeys and Man, but of the 'Deciduata', 

 defined as above, from the remainder of the placental mammals. 

 There is also a third possible hypothesis. Leaving open the 

 question as to whether the placenta of the Carnivora can, or 

 cannot be derived from an Ungulate condition, we may separate 

 them from the remaining four groups, the placentae of which 

 have obviously several characters in common. This will result in 

 the re-establishment of the group of Discoplacentalia (without the 

 Lemurs) provided that that arrangement can be sustained on 

 general anatomical grounds. 



