CHAPTER X. 



AMONG the birds there is also a graduated series 

 of water trespassers, corresponding in many ways to 

 the mammalia which have just been described. 



There are none, however, which correspond with 

 the whale tribe, in living entirely in the water ; and 

 this for obvious reasons. The whales are enabled to 

 produce their young in the water ; and as the little 

 creatures are born alive and in the full enjoyment of 

 their muscular power, they can swim as soon as they 

 see the light, and can accompany their mothers. The 

 birds, however, lay eggs, which must be hatched by 

 constant and regular warmth. This requisite cannot 

 be supplied in the sea ; and, in consequence, the bird 

 is obliged to go on shore for the purpose of depositing 

 and hatching its eggs. 



The most aquatic of birds are undoubtedly the 

 Penguins, which pass almost the whole of their time 

 in the water, and seldom come on shore except for 

 breeding purposes. They may therefore be considered 

 as analogous to the seals, which live almost entirely in 

 the water, but sleep on the land, and go ashore to 

 nurture their young. 



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