ntic, but otherwise
completely related, forms. New Zealand has no indigenous mammalia, but in
their place great cursorial birds with but rudimentary wings. Exactly the
same thing is found by geology in its tertiary and post-tertiary strata:
nowhere a mammal, but gigantic birds with rudimentary {70} wings, down to
the dinornis, which probably died out in man's time. New Holland has merely
marsupial and some monotrematous, but no placental, mammalia; even its
tertiary strata give no placental mammalia, but marsupialia, in analogy
with all living genera, herbivorous, and carnivorous. Indeed, the analogy
goes so far that the same line which through the Indian Archipelago
separates the present Australian animal and plant world from the Asiatic,
forms also the separating line for the geological zones of the Pliocene
epoch. All these are facts which render quite inevitable the idea of an
origin of the higher organic species of to-day through descent.

But still, from another side, animal geography, though it does not yet
speak for a common pedigree of the whole animal world, as the facts just
mentioned also do not, still at least speaks for a descent of related,
though at present separated, genera and species from common forefathers.
The continents of the Old and New World are so constructed that toward the
North Pole they approach one another very closely, and toward the South
Pole they withdraw from one another. Without doubt there existed in the
North, through long periods of time, a land-connection of America with Asia
and with Europe. Now, both continents have their more or less
characteristic animal world, and these characteristics are distributed over
the two halves of the globe in the following extremely remarkable way: The
fauna of the Old and the New World, in those groups of animal genera which
live only in the warmer or tropic zones or only south of the equator, and
have no associates of genera or families in the higher North, is in each
hemisphere entirely characteristic, and differs in a {71} marked way from
the fauna of the other half of the globe. For instance, the rhinoceros, the
hippopotamus, the giraffe, the antelope with undivided horns, the hedgehog,
the mole proper, are only inhabitants of the Old World, whence also the
horse originally came, the striped ones in Africa and the non-striped in
Asia; on the other hand, the lemur, the ant-eater, the armadillo, and
others, are limited to South America. The apes