t during a succession of ages, and by alternations of
habits, all the species may change into each other, or one of them
give birth to all the rest. Yet to these persons the following
answer may be given from their own system: If the species have
changed by degrees, as they assume, we ought to find traces of this
gradual modification. Thus, between the Palaeotherium and the species
of our own days, we should be able to discover some intermediate
forms; and yet no such discovery has ever been made. Since the
bowels of the earth have not preserved monuments of this strange
genealogy, we have a right to conclude that the ancient and now
extinct species were as permanent in their forms and characters as
those which exist at present; or, at least, that the catastrophe
which destroyed them did not have sufficient time for the production
of the changes that are alleged to have taken place."

Cuvier thus emphatically rejects all idea that any of the tertiary
mammals could have been the ancestral forms of those now existing.

"From all these well-established facts, there does not seem to be
the smallest foundation for supposing that the new genera which I
have discovered or established among extraneous fossils, such as the
_palaeotherium_, _anaplotherium_, _megalonynx_, _mastodon_,
_pterodactylis_, etc., have ever been the sources of any of our
present animals, which only differ as far as they are influenced by
time or climate. Even if it should prove true, which I am far from
believing to be the case, that the fossil elephants, rhinoceroses,
elks, and bears do not differ further from the present existing
species of the same genera than the present races of dogs differ
among themselves, this would by no means be a sufficient reason to
conclude that they were of the same species; since the races or
varieties of dogs have been influenced by the trammels of
domestication, which these other animals never did and indeed never
could experience."[102]

The extreme views of Cuvier as to the frequent renewal and extinction of
life were afterward (in 1850) carried out to an exaggerated extent by
D'Orbigny, who maintained that the life of the earth must have become
extinct and again renewed twenty-seven times. Similar views were held by
Agassiz, who, however, maintained the geological succession of animals
and the parallelism between their embryonic development and geological
succe