Geographical Distribution. 225 



pean forms. Lastly, there are 480 known species of 

 plants, of which 40 are peculiar, though allied to 

 European species. 



Bermudas. — A small volcanic group of islands, 700 

 miles from North Carolina. Although there are 

 about 100 islands in the group, their total area does 

 not exceed 50 square miles. The group is surrounded 

 by water varying in depth from 2,500 to 3,800 fathoms. 

 The only terrestrial Vertebrate (unless the rats and 

 mice are indigenous) is a lizard allied to an American 

 form, but specifically distinct from it, and therefore a 

 solitary species which does not occur anywhere else in 

 the world. None of the birds or bats are peculiar, 

 any more than in the case of the Azores ; but, as in 

 that case, a large percentage of the land-shells are so 

 — namely, at least one quarter of the whole. Neither 

 the botany nor the entomology of this group has been 

 worked out ; but I have said enough to show how re- 

 markably parallel are the cases of these two volcanic 

 groups of islands situated in different hemispheres, but 

 at about the same distance from large continents. In 

 both there is an extraordinary paucity of terrestrial 

 vertebrata, and of any peculiar species of bird or beast. 

 On the other hand, there is in both a marvellous 

 wealth of peculiar species of insects and land-shells. 

 Now these correlations are all abundantly intelligible. 

 It is a difficult matter for any terrestrial animal to 

 cross 900, or even 700, miles of ocean : therefore only 

 one lizard has succeeded in doing so in one of the two 

 parallel cases ; and. living cut off from intercrossing 

 with its parent form, the descendants of that lizard 

 have become modified so as to constitute a peculiar 

 species. But it is more easy for large flying animals 



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