n those of New
Zealand. Yet the most skilful naturalist from an examination of the {338}
species of the two countries could not have foreseen this result.

Agassiz insists that ancient animals resemble to a certain extent the
embryos of recent animals of the same classes; or that the geological
succession of extinct forms is in some degree parallel to the embryological
development of recent forms. I must follow Pictet and Huxley in thinking
that the truth of this doctrine is very far from proved. Yet I fully expect
to see it hereafter confirmed, at least in regard to subordinate groups,
which have branched off from each other within comparatively recent times.
For this doctrine of Agassiz accords well with the theory of natural
selection. In a future chapter I shall attempt to show that the adult
differs from its embryo, owing to variations supervening at a not early
age, and being inherited at a corresponding age. This process, whilst it
leaves the embryo almost unaltered, continually adds, in the course of
successive generations, more and more difference to the adult.

Thus the embryo comes to be left as a sort of picture, preserved by nature,
of the ancient and less modified condition of each animal. This view may be
true, and yet it may never be capable of full proof. Seeing, for instance,
that the oldest known mammals, reptiles, and fish strictly belong to their
own proper classes, though some of these old forms are in a slight degree
less distinct from each other than are the typical members of the same
groups at the present day, it would be vain to look for animals having the
common embryological character of the Vertebrata, until beds far beneath
the lowest Silurian strata are discovered--a discovery of which the chance
is very small.

_On the Succession of the same Types within the same {339} areas, during
the later tertiary periods._--Mr. Clift many years ago showed that the
fossil mammals from the Australian caves were closely allied to the living
marsupials of that continent. In South America, a similar relationship is
manifest, even to an uneducated eye, in the gigantic pieces of armour like
those of the armadillo, found in several parts of La Plata; and Professor
Owen has shown in the most striking manner that most of the fossil mammals,
buried there in such numbers, are related to South American types. This
relationship is even more clearly seen in the wonderful collection of
fossil bones made by MM.