GEOGRAPHICAL DISTRIBUTION OF ANIMALS 



birds, which cross great stretches of the ocean with ease. 

 Though the land birds belong to peculiar species, and most 

 of them to peculiar genera, they are nevertheless of unmis- 

 takably South American types and belong to South American 

 families. Large lizards, one a land species and the other 

 marine, as well as the huge land tortoises that have given 

 their name to the islands, are abundant. When the islands 

 were first discovered there were fifteen species of these mon- 

 strous tortoises, each island and islet having its own species, 

 but many of these have been extirpated. The species of land 

 birds, like those of the tortoises, are peculiar to a single 

 island each ; the genera are mostly common to the group, as 

 the islands are so far apart that communication between 

 them is difficult. 



On the theory of evolution these remarkable facts are 

 easily explained. The ancestors of the existmg birds and 

 reptiles came, rarely and at long intervals, from the main- 

 land of South America, and after settling in the islands 

 became slowly modified, so that they were placed in genera 

 nearly allied to those of the continent, yet different from 

 them; and, in the isolation of the individual islands the spe- 

 cies were free to develop into new forms peculiar to each. 



In the Galapagos we witness the results of what may be 

 called a great evolutionary experiment, under conditions 

 unaffected by human interference, and such conditions are 

 rare; but the Cape Verde islands, in the Atlantic, display 

 very similar relations in their animals and plants. The 

 species there are peculiar, but their affinity is as unmistak- 

 ably African as that of the Galapagos species is South 

 American. 



Bermuda and Madeira are almost as far from the North 

 American and African coasts, respectively, as the Galapagos 

 Islands are from Ecuador, but they have hardly any peculiar 



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