io6 WILD LIFE OF SCOTLAND 



hound, and of two embryos in that of the porbeagle. 

 And, although eggs and young are matured from 

 time to time, in no case can the number be other-* 

 wise than trifling. The hard cases of the eggs, 

 and the fact of the young being born alive, doubt- 

 less help to protect them from many risks. 



Side by side with those of the cod, the eggs are 

 monstrous. So large are they, and so much food 

 yolk do they contain, that the thrifty Swedes are 

 said to find in those of the dog-fish, a convenient 

 substitute for hens' eggs. I am not aware that 

 they are so used in this country, but the hint is 

 worth considering. 



The step from the fishes to the marine mammals 

 is a considerable one. It takes us from animals 

 which breathe through gills in the water, and are 

 cold-blooded, to warm-blooded and air-breathing 

 animals. Moreover, the mammals, as their very 

 name implies, not only bring forth the young alive, 

 but also nurse them through the earlier, and more 

 tender stages. 



There seems reason to believe that these pre- 

 datory mammals were once land animals, which, 

 at some distant date, after a long period of terres- 

 trial progression, and for some reason, probably 

 connected with food-supply, took to the water. 



