Again, Euphorbia, a mundane or
widely distributed genus, has here eight species, of which seven
are confined to the archipelago, and not one found on any two
islands: Acalypha and Borreria, both mundane genera, have
respectively six and seven species, none of which have the same
species on two islands, with the exception of one Borreria, which
does occur on two islands. The species of the Compositae are
particularly local; and Dr. Hooker has furnished me with several
other most striking illustrations of the difference of the species
on the different islands. He remarks that this law of distribution
holds good both with those genera confined to the archipelago, and
those distributed in other quarters of the world: in like manner we
have seen that the different islands have their proper species of
the mundane genus of tortoise, and of the widely distributed
American genus of the mocking-thrush, as well as of two of the
Galapageian sub-groups of finches, and almost certainly of the
Galapageian genus Amblyrhynchus.
The distribution of the tenants of this archipelago would not be
nearly so wonderful, if, for instance, one island had a
mocking-thrush, and a second island some other quite distinct
genus;--if one island had its genus of lizard, and a second island
another distinct genus, or none whatever;--or if the different
islands were inhabited, not by representative species of the same
genera of plants, but by totally different genera, as does to a
certain extent hold good; for, to give one instance, a large
berry-bearing tree at James Island has no representative species in
Charles Island.
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