de Candolle, to distinct genera. In
the Galapagos Archipelago, many even of the birds, though so well adapted
for flying from island to island, differ on the different islands; thus
there are three closely allied species of mocking-thrush, each confined to
its own island. Now let us suppose the mocking-thrush of Chatham Island to
be blown to Charles Island, which has its own mocking-thrush; why should it
succeed in establishing itself there? We may safely infer that Charles
Island is well stocked with its own species, for annually more eggs are
laid and young birds hatched than can possibly be reared; and we may infer
that the mocking-thrush peculiar to Charles Island is at least as well
fitted for its home as is the species peculiar to Chatham Island. Sir C.
Lyell and Mr. Wollaston have communicated to me a remarkable fact bearing
on this subject; namely, that Madeira and the adjoining islet of Porto
Santo possess many distinct but representative species of land-shells, some
of which live in crevices of stone; and although large quantities of stone
are annually transported from Porto Santo to Madeira, yet this latter
island has not become colonised by the Porto Santo species: nevertheless,
both islands have been colonised by some European land-shells, which no
doubt had some advantage over the indigenous species. From these
considerations I think we need not greatly marvel at the endemic species
which inhabit the several islands of the Galapagos Archipelago not having
all spread from island to island.
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