EVIDENCES FROM GEOGRAPHIC DISTRIBUTION 175 



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 pecuUar, 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 remarkably 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 pecuUar 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 to cross those distances of ocean: consequently, there is only 

 one instance of a peculiar species of bird or bat — namely, a bull-finch 

 in the Azores, which, being a small land-bird, is not likely ever to have 

 had any other visitors from its original parent species coming over 

 from Europe to keep up the original breed. Lastly, it is very much more 

 easy for insects and land-moUusca to be conveyed to such islands by 

 wind and floating timber than it is for terrestrial mammals, or even 

 than it is for small birds and bats; but yet such means of transit are 

 not sufficiently sure to admit of much recruiting from the mainland 

 for the purpose of keeping up the specific types. Consequently, the 

 insects and the land-shells present a much greater proportion of 

 peculiar species — namely, one half and one fourth of the land-shells in 

 the one case, and one eighth of the beetles in the other. All these cor- 

 relations, I say, are abundantly intelligible on the theory of evolution; 

 but who shall explain, on the opposite theory, why orders of beetles 

 and land-mollusca should have been chosen from among all other 

 animals for such superabundant creation on oceanic islands, so that 

 in the Azores alone we find no less than 32 of the one and 14 of the 

 other? And, in this connection, I may again allude to the peculiar 

 species of beetles in the island of Madeira. Here there are an enor- 

 mous number of peculiar species, though they are nearly all related to, 



