ct forms often tend to fill up gaps between
existing forms, sometimes blending two groups previously classed as
distinct into one; but more commonly only bringing them a little closer
together. The more ancient a form is, the more often, apparently, it
displays characters in some degree intermediate between groups now
distinct; for the more ancient a form is, the more nearly it will be
related to, and consequently resemble, the common progenitor of groups,
since {345} become widely divergent. Extinct forms are seldom directly
intermediate between existing forms; but are intermediate only by a long
and circuitous course through many extinct and very different forms. We can
clearly see why the organic remains of closely consecutive formations are
more closely allied to each other, than are those of remote formations; for
the forms are more closely linked together by generation: we can clearly
see why the remains of an intermediate formation are intermediate in
character.

The inhabitants of each successive period in the world's history have
beaten their predecessors in the race for life, and are, in so far, higher
in the scale of nature; and this may account for that vague yet ill-defined
sentiment, felt by many palaeontologists, that organisation on the whole has
progressed. If it should hereafter be proved that ancient animals resemble
to a certain extent the embryos of more recent animals of the same class,
the fact will be intelligible. The succession of the same types of
structure within the same areas during the later geological periods ceases
to be mysterious, and is simply explained by inheritance.

If then the geological record be as imperfect as I believe it to be, and it
may at least be asserted that the record cannot be proved to be much more
perfect, the main objections to the theory of natural selection are greatly
diminished or disappear. On the other hand, all the chief laws of
palaeontology plainly proclaim, as it seems to me, that species have been
produced by ordinary generation: old forms having been supplanted by new
and improved forms of life, produced by the laws of variation still acting
round us, and preserved by Natural Selection.

* * * * *

{346}

CHAPTER XI.

GEOGRAPHICAL DISTRIBUTION.

Present distribution cannot be accounted for by differences in physical
conditions--Importance of barriers--Affinity of the productions of the
same continent