,--and if in both regions the species
have gone on slowly changing during the accumulation of the several
formations and during the long intervals of time between them; in this
case, the several formations in the two regions could be arranged in
the same order, in accordance with the general succession of the form
of life, and the order would falsely appear to be strictly parallel;
nevertheless the species would not all be the same in the apparently
corresponding stages in the two regions.

ON THE AFFINITIES OF EXTINCT SPECIES TO EACH OTHER, AND TO LIVING FORMS.

Let us now look to the mutual affinities of extinct and living species.
They all fall into one grand natural system; and this fact is at once
explained on the principle of descent. The more ancient any form is, the
more, as a general rule, it differs from living forms. But, as Buckland
long ago remarked, all fossils can be classed either in still existing
groups, or between them. That the extinct forms of life help to fill up
the wide intervals between existing genera, families, and orders, cannot
be disputed. For if we confine our attention either to the living or
to the extinct alone, the series is far less perfect than if we combine
both into one general system. With respect to the Vertebrata, whole
pages could be filled with striking illustrations from our great
palaeontologist, Owen, showing how extinct animals fall in between
existing groups. Cuvier ranked the Ruminants and Pachyderms, as the two
most distinct orders of mammals; but Owen has discovered so many fossil
links, that he has had to alter the whole classification of these two
orders; and has placed certain pachyderms in the same sub-order with
ruminants: for example, he dissolves by fine gradations the apparently
wide difference between the pig and the camel. In regard to the
Invertebrata, Barrande, and a higher authority could not be named,
asserts that he is every day taught that palaeozoic animals, though
belonging to the same orders, families, or genera with those living at
the present day, were not at this early epoch limited in such distinct
groups as they now are.

Some writers have objected to any extinct species or group of species
being considered as intermediate between living species or groups. If by
this term it is meant that an extinct form is directly intermediate in
all its characters between two living forms, the objection is probably
valid. But I apprehend that in a perfectly