A FROZEN WORLD 205 



fresh-water mussels can ascend the river into the 

 brook, and pass by the brook into the pond, 

 which has thus a direct line of communication 

 with all waters elsewhere, including even the great 

 oceans. But the pond without an outlet cannot 

 thus be peopled. Whatever inhabitants it possesses 

 have come to it much more by pure chance. They 

 are not able to walk overland from one pond to 

 another ; they must be brought there somehow, 

 by insignificant accidents. Regarded in this light, 

 the original peopling of every pond in England is 

 a problem in itself a problem analogous in its 

 own petty way to the problem of the peopling of 

 oceanic islands. 



That great and accomplished and ingenious 

 naturalist, Mr. Alfred Russel Wallace, working 

 in part upon lines long since laid down by 

 Darwin, has shown us in detail how oceanic 

 islands have in each case come to be peopled. 

 He has shown us how they never contain any 

 large indigenous land animals belonging to the 

 great group of mammals any deer or elephants 

 or pigs or horses ; because mammals, being born 

 alive, cannot, of course, be transported in the 

 egg, and because the adult beasts could seldom 

 be carried across great stretches of ocean by 

 accident without perishing on the way of cold, 

 hunger, or drowning. One can hardly imagine 

 an antelope or a buffalo conveyed safely over 

 sea by natural causes from Africa to the Cape 

 Verdes, or from America to the Bermudas. As 

 a matter of fact, therefore, the natural population 



