These
Two Latter Species Are Closely Allied, And Would By Some
Ornithologists Be Considered As Only Well-Marked Races Or
Varieties; but the Mimus trifasciatus is very distinct.
Unfortunately most of the specimens of the finch tribe were
mingled together;
But I have strong reasons to suspect that
some of the species of the sub-group Geospiza are confined
to separate islands. If the different islands have their
representatives of Geospiza, it may help to explain the
singularly large number of the species of this sub-group in this
one small archipelago, and as a probable consequence of their
numbers, the perfectly graduated series in the size of their
beaks. Two species of the sub-group Cactornis, and two of
the Camarhynchus, were procured in the archipelago; and
of the numerous specimens of these two sub-groups shot by
four collectors at James Island, all were found to belong to
one species of each; whereas the numerous specimens shot
either on Chatham or Charles Island (for the two sets were
mingled together) all belonged to the two other species:
hence we may feel almost sure that these islands possess
their respective species of these two sub-groups. In land-
shells this law of distribution does not appear to hold good.
In my very small collection of insects, Mr. Waterhouse
remarks, that of those which were ticketed with their locality,
not one was common to any two of the islands.
If we now turn to the Flora, we shall find the aboriginal
plants of the different islands wonderfully different. I give
all the following results on the high authority of my friend
Dr. J. Hooker. I may premise that I indiscriminately collected
everything in flower on the different islands, and fortunately
kept my collections separate. Too much confidence,
however, must not be placed in the proportional results, as
the small collections brought home by some other naturalists
though in some respects confirming the results, plainly show
that much remains to be done in the botany of this group:
the Leguminosae, moreover, has as yet been only approximately
worked out: -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Number of
Species
confined
to the
Number of Number of Galapagos
species species Number Archipelago
Total found in confined confined but found
Name Number other to the to the on more
of of parts of Galapagos one than the
Island Species the world Archipelago island one island
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
James 71 33 38 30 8
Albemarle 4 18 26 22 4
Chatham 32 16 16 12 4
Charles 68 39 29 21 8
(or 29, if
the probably
imported
plants be
subtracted.)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Hence we have the truly wonderful fact, that in James
Island, of the thirty-eight Galapageian plants, or those found
in no other part of the world, thirty are exclusively confined
to this one island; and in Albemarle Island, of the twenty-
six aboriginal Galapageian plants, twenty-two are confined
to this one island, that is, only four are at present known to
grow in the other islands of the archipelago; and so on, as
shown in the above table, with the plants from Chatham and
Charles Islands. This fact will, perhaps, be rendered even
more striking, by giving a few illustrations: - thus, Scalesia,
a remarkable arborescent genus of the Compositae, is confined
to the archipelago: it has six species: one from Chatham,
one from Albemarle, one from Charles Island, two from
James Island, and the sixth from one of the three latter
islands, but it is not known from which: not one of these six
species grows on any two islands. 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. But it is the
circumstance, that several of the islands possess their own
species of the tortoise, mocking-thrush, finches, and numerous
plants, these species having the same general habits,
occupying analogous situations, and obviously filling the
same place in the natural economy of this archipelago, that
strikes me with wonder. It may be suspected that some of
these representative species, at least in the case of the
tortoise and of some of the birds, may hereafter prove to be
only well-marked races; but this would be of equally great
interest to the philosophical naturalist. I have said that most
of the islands are in sight of each other: I may specify that
Charles Island is fifty miles from the nearest part of Chatham
Island, and thirty-three miles from the nearest part of
Albemarle Island. Chatham Island is sixty miles from the
nearest part of James Island, but there are two intermediate
islands between them which were not visited by me.
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