288 THE MAMMALIA. 



entirely different mode of life, inasmuch as it 

 burrows in the ground for certain kinds of mussels. 

 All the others hunt for fish, which they can readily 

 tear to pieces with their sharp canine teeth and 

 pointed molars, which are compressed somewhat to 

 the side. 



Of fossils that might illustrate the gradual in- 

 coming of Seals there are none. We conclude that 

 the process must, at one time, have begun with 

 carnivorous land-animals. The idea that the re- 

 verse might have been the case by their having, as 

 sea-animals, taken to a life on land, has as little 

 value here as in the case of the Cetaceans, which 

 are mammals, and have never been anything else. 

 The period during which they changed their element 

 lies at an immeasurable distance in the far past, 

 but is probably less distant than that in which the 

 ancestors of the whales took to the sea while re- 

 ducing their hind limbs. 



There can be no question about making the 

 Whales (of course only the toothed group) the 

 primary parents of the Seals. If any comparison of 

 the kind is thought of, the Eocene Zeuglodonta could 

 alone be taken into consideration. But even these 

 latter do not show any points of connection ; their 

 skull would have to be retro-metamorphosed to form 



