the struggle for life
over other and preceding forms. If under a nearly similar climate, the
eocene inhabitants of one quarter of the world were put into competition
with the existing inhabitants of the same or some other quarter, the
eocene fauna or flora would certainly be beaten and exterminated;
as would a secondary fauna by an eocene, and a palaeozoic fauna by a
secondary fauna. I do not doubt that this process of improvement has
affected in a marked and sensible manner the organisation of the more
recent and victorious forms of life, in comparison with the ancient and
beaten forms; but I can see no way of testing this sort of progress.
Crustaceans, for instance, not the highest in their own class, may have
beaten the highest molluscs. From the extraordinary manner in which
European productions have recently spread over New Zealand, and have
seized on places which must have been previously occupied, we may
believe, if all the animals and plants of Great Britain were set free
in New Zealand, that in the course of time a multitude of British forms
would become thoroughly naturalized there, and would exterminate many
of the natives. On the other hand, from what we see now occurring in New
Zealand, and from hardly a single inhabitant of the southern hemisphere
having become wild in any part of Europe, we may doubt, if all the
productions of New Zealand were set free in Great Britain, whether any
considerable number would be enabled to seize on places now occupied by
our native plants and animals. Under this point of view, the productions
of Great Britain may be said to be higher than those of New Zealand. Yet
the most skilful naturalist from an examination of the 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 superv