130 THE STORY OF LIFE IN THE SEAS. 



openings. Like all other Mammals the Cetaceans 

 bring forth their young alive, suckle them, and 

 breathe air by means of lungs. But there can be 

 no doubt that they are extremely modified for 

 their aquatic life. The characteristic covering of 

 Mammals the hairs is, in the adult condition 

 of the Whales, entirely wanting, and is repre- 

 sented in other members of the Class by only 

 a few bristles on the snout. The heat of the 

 body is maintained by a thick coat of fat, called 

 the blubber, lying immediately beneath the skin, 

 and this yields, on boiling, a valuable oil, which 

 helps to support the whale-fishermen. One of 

 the most striking modifications, however, is the 

 loss of the hind limbs. It is only in some species 

 that even rudiments of these have been found. 

 All of these facts indicate that the Cetaceans 

 must have taken to a mode of life in the water a 

 very long time ago, and the study of the rocks 

 proves the existence of Whales as far back as 

 Eocene times, but it is of interest to note that, 

 in some respects, the oldest fossil Cetaceans are 

 less specialised than those that are now living. 



The class of Mammals called the Carnivora 

 includes the Cats, Dogs, Ferrets and many other 

 animals which are purely terrestrial, but one of 

 its divisions is entirely composed of those well- 

 known aquatic animals the Seals and the Walrus. 

 If we take the common Seal as an example of 

 this group, and compare it with the Porpoise, as 

 a representative of the Cetaceans, we find that in 

 habits as well as in anatomy the former is less 

 completely changed than the latter. The Seal 

 frequently comes to land to bask in the sun, or 



