ITS PLACE IN NATUEE. 11 



division of Eutheria, which includes all existing 

 mammals except the Marsupials and Monotremes. 

 In treating only of existing mammals, a division 

 of the class into distinctly circumscribed groups is 

 perfectly easy. The so-called orders generally ac- 

 cepted are separated from each other by well- 

 marked breaks of continuity. Many extinct forms 

 can also be contained within the definitions of these 

 orders. But the rapid advance of palaeontology is 

 disclosing to view an enormous number of long- 

 buried animal forms, which are gradually filling up 

 all the spaces left between the isolated groups now 

 surviving on the earth, and continually increasing 

 the difficulty of giving satisfactory definitions of 

 their boundaries. 



In the first serious attempt at the classification of 

 the Mammalia, that of John Ray, in his "Synopsis 

 Methodica Animahum," published in 1693, the class 

 was separated into two great divisions, the ungulated 

 or hoofed animals, and the unguiculated, or those 

 with nails or claws. This division, especially as 

 applied by its author, was somewhat artificial, the 

 camel being separated from all its ungulate allies, and 

 placed in the unguiculate division, and the latter 

 embracing a very heterogeneous assemblage of crea- 

 tures. Nevertheless, some portion of this system 

 has survived, and especially the group JJnguJata, dis- 



