They dominated until reptiles appeared, when
they mostly gave place to (or, as the derivationists will insist, were
resolved by divergent variation and natural selection into) common
fishes, destitute of reptilian characters, and saurian reptiles--the
intermediate grades, which, according to a familiar piscine saying, are
"neither fish, flesh, nor good red-herring," being eliminated and
extinguished by natural consequence of the struggle for existence which
Darwin so aptly portrays. And so, perhaps, of the other prophetic
types. Here type and antitype correspond. If these are true prophecies,
we need not wonder that some who read them in Agassizs book will read
their fulfillment in Darwins.
Note also, in this connection, that along with a wonderful persistence
of type, with change of species, genera, orders, etc., from formation
to formation, no species and no higher group which has once
unequivocally died out ever afterward reappears. Why is this, but that
the link of generation has been sundered? Why, on the hypothesis of
independent originations, were not failing species recreated, either
identically or with a difference, in regions eminently adapted to their
well-being? To take a striking case. That no part of the world now
offers more suitable conditions for wild horses and cattle than the
pampas and other plains of South America, is shown by the facility with
which they have there run wild and enormously multiplied, since
introduced from the Old World not long ago.
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