REOAPITULATION. 493 



closely similar as the same species ever require, we need 

 feel no surprise at their inhabitants being widely different, 

 if they have been for a long period completely sundered 

 from each other; for as the relation of organism to organ- 

 ism is the most important of all relations, and as the two 

 countries will have received colonists at various periods 

 and in different proportions, from some other country or 

 from each other, the course of modification in the two 

 areas will inevitably have been different. 



On this view of migration, with subsequent modifica- 

 tion, we see why oceanic islands are inhabited by only few 

 species, but of these, why many are peculiar or endemic 

 forms. We clearly see why species belonging to those 

 groups of animals which cannot cross wide spaces of the 

 ocean, as frogs and terrestrial mammals, do not inhabit 

 oceanic islands; and why, on the other hand, new and 

 peculiar species of bats, animals which can traverse the 

 ocean, are often found on islands far distant from any con- 

 tinent. Such cases as the presence of peculiar species of 

 bats on oceanic islands and the absence of all other terres- 

 trial mammals, are facts utterly inexplicable on the theory 

 of independent acts of creation. 



The existence of closely allied representative species in 

 any two areas, implies, on the theory of descent with 

 modification, that the same parent-forms formerly inhab- 

 ited both areas: and we almost invariably find that wher- 

 ever many closely allied species inhabit two areas, some 

 identical species are still common to both. Wherever 

 many closely allied yet distinct species occur, doubtful 

 forms and varieties belonging to the same groups likewise 

 occur. It is a rule of high generality that the inhabitants 

 of each area are related to the inhabitants of the nearest 

 source whence immigrants might have been derived. We 

 see this in the, striking relation of nearly all the plants and 

 animals of the Galapagos Archipelago, of Juan Fernandez, 

 and of the other American islands, to the plants and 

 animals of the neighboring American mainland; and of 

 those of the Cape de Verde Archipelago, and of the other 

 African islands to the African mainland. It must be ad- 

 mitted that these facts receive no explanation on the 

 theory of creation. •,,,-, 



The fact, as we have seen, that all past and present 



