mals and of plants, thus bridge over the
interval between the present and the Mesozoic periods, is it possible
that the majority of other living things underwent a "sea-change into
something new and strange" all at once?

[Footnote 1: See an article in the _Saturday Review_, for 1858, on
"Chalk, Ancient and Modern."]

6. Thus far I have endeavoured to expand and to enforce by fresh
arguments, but not to modify in any important respect, the ideas
submitted to you on a former occasion. But when I come to the
propositions touching progressive modification, it appears to me, with
the help of the new light which has broken from various quarters, that
there is much ground for softening the somewhat Brutus-like severity with
which, in 1862, I dealt with a doctrine, for the truth of which I should
have been glad enough to be able to find a good foundation. So far,
indeed, as the _Invertebrata_ and the lower _Vertebrata_ are concerned,
the facts and the conclusions which are to be drawn from them appear to
me to remain what they were. For anything that, as yet, appears to the
contrary, the earliest known Marsupials may have been as highly organised
as their living congeners; the Permian lizards show no signs of
inferiority to those of the present day; the Labyrinthodonts cannot be
placed below the living Salamander and Triton; the Devonian Ganoids are
closely related to _Polypterus_ and to _Lepidosiren_.

But when we turn to the higher _Vertebrata_, the results of recent
investigations, however we may sift and criticise them, seem to me to
leave a clear balance in favour of the doctrine of the evolution of
living forms one from another. Nevertheless, in discussing this question,
it is very necessary to discriminate carefully between the different
kinds of evidence from fossil remains which are brought forward in favour
of evolution.

Every fossil which takes an intermediate place between forms of life
already known, may be said, so far as it is intermediate, to be evidence
in favour of evolution, inasmuch as it shows a possible road by which
evolution may have taken place. But the mere discovery of such a form
does not, in itself, prove that evolution took place by and through it,
nor does it constitute more than presumptive evidence in favour of
evolution in general. Suppose A, B, C to be three forms, while B is
intermediate in structure between A and C. Then the doctrine of evolution
offers four possible alternatives. A ma