fish is
common to the above-named three approximate faunas of Eastern and Western
America and the eastern Pacific islands, yet many fish range from the
Pacific into the Indian Ocean, and many shells are common to the eastern
islands of the Pacific {349} and the eastern shores of Africa, on almost
exactly opposite meridians of longitude.

A third great fact, partly included in the foregoing statements, is the
affinity of the productions of the same continent or sea, though the
species themselves are distinct at different points and stations. It is a
law of the widest generality, and every continent offers innumerable
instances. Nevertheless the naturalist in travelling, for instance, from
north to south never fails to be struck by the manner in which successive
groups of beings, specifically distinct, yet clearly related, replace each
other. He hears from closely allied, yet distinct kinds of birds, notes
nearly similar, and sees their nests similarly constructed, but not quite
alike, with eggs coloured in nearly the same manner. The plains near the
Straits of Magellan are inhabited by one species of Rhea (American
ostrich), and northward the plains of La Plata by another species of the
same genus; and not by a true ostrich or emu, like those found in Africa
and Australia under the same latitude. On these same plains of La Plata, we
see the agouti and bizcacha, animals having nearly the same habits as our
hares and rabbits and belonging to the same order of Rodents, but they
plainly display an American type of structure. We ascend the lofty peaks of
the Cordillera and we find an alpine species of bizcacha; we look to the
waters, and we do not find the beaver or musk-rat, but the coypu and
capybara, rodents of the American type. Innumerable other instances could
be given. If we look to the islands off the American shore, however much
they may differ in geological structure, the inhabitants, though they may
be all peculiar species, are essentially American. We may look back to past
ages, as shown in the last chapter, and we find American types then
prevalent on {350} the American continent and in the American seas. We see
in these facts some deep organic bond, prevailing throughout space and
time, over the same areas of land and water, and independent of their
physical conditions. The naturalist must feel little curiosity, who is not
led to inquire what this bond is.

This bond, on my theory, is simply inheritance, that c