Jones's admirable account of Bermuda, that very many North American birds occasionally or even frequently visit this island.

Almost every year, as I am informed by Mr.E.V.Harcourt, many European and African birds are blown to Madeira; this island is inhabited by ninety-nine kinds, of which one alone is peculiar, though very closely related to a European form; and three or four other species are confined to this island and to the Canaries.
So that the islands of Bermuda and Madeira have been stocked from the neighbouring continents with birds, which for long ages have there struggled together, and have become mutually co-adapted.

Hence, when settled in their new homes, each kind will have been kept by the others to its proper place and habits, and will consequently have been but little liable to modification.

Any tendency to modification will also have been checked by intercrossing with the unmodified immigrants, often arriving from the mother-country.

Madeira again is inhabited by a wonderful number of peculiar land-shells, whereas not one species of sea-shell is peculiar to its shores: now, though we do not know how sea-shells are dispersed, yet we can see that their eggs or larvae, perhaps attached to seaweed or floating timber, or to the feet of wading birds, might be transported across three or four hundred miles of open sea far more easily than land-shells.