e luxuriant as we go south but not altering in
essential character, so that when we reach Alabama or Florida we still find
ourselves in the midst of pines, oaks, sumachs, magnolias, vines, and other
characteristic forms of the temperate flora; while the birds, insects, and
land-shells are of the same general character with those found further
north.[1] But if we now cross over the narrow strait, about fifty miles
wide, which separates Florida from the Bahama Islands, we find ourselves in
a totally different country, surrounded by a vegetation which is
essentially tropical and generally identical with that of Cuba. The change
is most striking, because there is little difference of climate, of soil,
or apparently of position, to account for it; and when we find that the
birds, the insects, and especially the land-shells of the Bahamas are
almost all West Indian, while the North American types of plants and
animals have almost all completely disappeared, we shall be convinced that
such differences and resemblances cannot be due to existing conditions, but
must depend upon laws and causes to which mere proximity of position offers
no clue.

Hardly less uncertain and irregular are the effects of climate. Hot
countries usually differ widely from cold ones in all their organic forms;
but the difference is by no means constant, nor does it bear any proportion
to difference of temperature. Between frigid Canada and sub-tropical
Florida there are less marked differences in the animal productions than
between Florida and Cuba or Yucatan, so much more alike in climate and so
much nearer together. So the differences between the birds and quadrupeds
of temperate Tasmania and tropical North {6} Australia are slight and
unimportant as compared with the enormous differences we find when we pass
from the latter country to equally tropical Java. If we compare
corresponding portions of different continents, we find no indication that
the almost perfect similarity of climate and general conditions has any
tendency to produce similarity in the animal world. The equatorial parts of
Brazil and of the West Coast of Africa are almost identical in climate and
in luxuriance of vegetation, but their animal life is totally diverse. In
the former we have tapirs, sloths, and prehensile-tailed monkeys; in the
latter elephants, antelopes, and man-like apes; while among birds, the
toucans, chatterers, and humming-birds of Brazil are replaced by the
planta