one ought to find traces of these gradual modifications.[64]
Palaeontology does not furnish such traces. Again, the limits of
variation, even under domestication, are narrow, and the most extreme
variation does not fundamentally alter the specific type. Thus the dog
has varied perhaps most of all, in size, in shape, in colour. "But
throughout all these variations the relations of the bones remain the
same, and the form of the teeth never changes to an appreciable
extent; at most there are some individuals in which an additional
false molar develops on one side or the other."[65] This second
objection is the objection of the morphologist. It would be an
interesting study to compare Cuvier's views on variation with those of
Darwin, who was essentially a systematist.

Cuvier's first objection was of course determined to some extent by
the imperfection of the palaeontological knowledge of his time. But
even at the present day the objection has a certain force, for
although we have definite evidence of many serial transformations of
one species into another along a single line, for example, Neumayr's
_Paludina_ series, yet at any one geological level the species, the
lines of descent, are all distinct from one another.[66]

Cuvier recognised very clearly that there is a succession of forms in
time, and that on the whole the most primitive forms are the earliest
to appear. Mammals are later than reptiles, and fishes appear earlier
than either. As Deperet puts it, "Cuvier not only demonstrated the
presence in the sedimentary strata of a series of terrestrial faunas
superimposed and distinct, but he was the first to express, and that
very clearly, the idea of the gradual increase in complexity of these
faunas from the oldest to the most recent" (p. 10).

He did not believe that the fauna of one epoch was transformed into
the fauna of the next. He explained the disappearance of the one by
the hypothesis of sudden catastrophes, and the appearance of the next
by the hypothesis of immigration. He nowhere advanced the hypothesis
of successive new creations. "For the rest, when I maintain that the
stony layers contain the bones of several genera and the earthy layers
those of several species which no longer exist, I do not mean that a
new creation has been necessary to produce the existing species, I
merely say that they did not exist in the same localities and must
have come thither from elsewhere."[67] It was left to d'Orbigny to