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 pal ontologists, 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 pal ontology 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.
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. Centres of creation. Means of dispersal, by changes of
climate and of the level of the land, and by occasional means.
Dispersal during the Glacial period co-extensive with the world.
In considering the distribution of organic beings over the face of the
260