rent circumstances--should all run, to a certain extent,
parallel with the systematic affinity of the forms which are subjected
to experiment; for systematic affinity attempts to express all kinds of
resemblance between all species.

First crosses between forms known to be varieties, or sufficiently alike
to be considered as varieties, and their mongrel offspring, are very
generally, but not quite universally, fertile. Nor is this nearly
general and perfect fertility surprising, when we remember how liable we
are to argue in a circle with respect to varieties in a state of nature;
and when we remember that the greater number of varieties have
been produced under domestication by the selection of mere external
differences, and not of differences in the reproductive system. In
all other respects, excluding fertility, there is a close general
resemblance between hybrids and mongrels. Finally, then, the facts
briefly given in this chapter do not seem to me opposed to, but even
rather to support the view, that there is no fundamental distinction
between species and varieties.

9. ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.

On the absence of intermediate varieties at the present day. On the
nature of extinct intermediate varieties; on their number. On the
vast lapse of time, as inferred from the rate of deposition and of
denudation. On the poorness of our palaeontological collections. On the
intermittence of geological formations. On the absence of intermediate
varieties in any one formation. On the sudden appearance of groups of
species. On their sudden appearance in the lowest known fossiliferous
strata.

In the sixth chapter I enumerated the chief objections which might be
justly urged against the views maintained in this volume. Most of them
have now been discussed. One, namely the distinctness of specific forms,
and their not being blended together by innumerable transitional links,
is a very obvious difficulty. I assigned reasons why such links do not
commonly occur at the present day, under the circumstances apparently
most favourable for their presence, namely on an extensive and
continuous area with graduated physical conditions. I endeavoured to
show, that the life of each species depends in a more important manner
on the presence of other already defined organic forms, than on climate;
and, therefore, that the really governing conditions of life do not
graduate away quite insensibly like heat or moistu