THE SEALS. 287 



Marsupials or Insectivora in the Trias down to the 

 present day, and which seems to have gradually 

 sent out off-shoots in the most different directions, 

 till at length they became unrecognisable. 



9. THE SEALS. 



According to the form of their skull, dentition, 

 and mode of life, Seals are ' carnivorous animals 

 that have adapted themselves to a life in water,' 

 and in this way they are generally described. In 

 order to make the theory acceptable, it is customary 

 to point to our Sea-otter, which, unlike its nearest 

 relative that thirsts for warm blood, has become a 

 pure fish-eater. The Sea-otter uses its hind limbs 

 after the manner of seals, and its skull shows a 

 depression of a similar kind to that which has 

 proved advantageous to the Seals. Hence, so it 

 is said, we have to imagine the ancestors of the 

 Seals on that line which has led them farther and 

 farther from their original forms, which very gra- 

 dually changed their limbs into fin- shaped rudders 

 (while perfectly retaining the pelvis and the articu- 

 lation of the skeleton), and whose skull became a 

 light, thin-walled box not burdened with strong 

 teeth. Only the Walrus (Trichechus) has developed 

 a couple of heavy tusks, corresponding with its 



