I.] MONODELPHIA. 9 



extinct South American Mesotherium t half Rodent and half 

 Ungulate, which leads by an easy transition to the still 

 more truly Ungulate Toxodon, for the reception of which a 

 distinct order (Toxodontid) has been proposed. 



The Insectivora and the Carnivora again are at present 

 quite distinct orders, but they merge into one another 

 through fossil forms, and are especially connected by the 

 large group of primitive Carnivora, so abundantly repre- 

 sented in the Eocene deposits both of America and Europe, 

 to which Cope has given the name of Creodonta. The 

 transition from the Insectivora to the Lemurs is not great, 

 and, strange to say, however different they now appear, the 

 early forms of Lemurs are not easily distinguished from the 

 primitive Ungulata. The Bats or Chiroptera are allied to 

 the Insectivora in all characters but the extraordinary 

 modification of their anterior extremities into wings ; but 

 this, like the want of the hind limbs in the Cetacea and 

 Sirenia, makes such a clear distinction between them and 

 all other Mammals, that, in the absence of any knowledge 

 of intermediate or transitional forms, they can be perfectly 

 separated, constituting as well-defined an order as any in 

 the class. 



Lastly, we have the important and well-characterised 

 group called Primates, including all the Monkeys and Man, 

 and the question is not yet solved as to how, and through 

 what forms, it is linked on to the other groups. It is com- 

 monly assumed that the Lemurs are nothing more than 

 inferior Primates, but the interval between them in the 

 actual fauna of the world is very great, and our knowledge 

 of numerous extinct species recently discovered in America, 

 said to be intermediate in character, is not yet sufficiently 

 perfect to enable us to form a definite opinion upon the 

 subject. 



