he new variety is so perfectly adapted to
the conditions that no improvement upon it is possible,--it will
persist, because, though it does not cease to vary, the varieties will
be inferior to itself.

If, as is more probable, the new variety is by no means perfectly
adapted to its conditions, but only fairly well adapted to them, it will
persist, so long as none of the varieties which it throws off are
better adapted than itself.

On the other hand, as soon as it varies in a useful way, _i.e._ when the
variation is such as to adapt it more perfectly to its conditions, the
fresh variety will tend to supplant the former.

So far from a gradual progress towards perfection forming any necessary
part of the Darwinian creed, it appears to us that it is perfectly
consistent with indefinite persistence in one state, or with a gradual
retrogression. Suppose, for example, a return of the glacial epoch and a
spread of polar climatal conditions over the whole globe. The operation
of natural selection under these circumstances would tend, on the whole,
to the weeding out of the higher organisms and the cherishing of the
lower forms of life. Cryptogamic vegetation would have the advantage
over Phanerogamic; _Hydrozoa_ over Corals; _Crustacea_ over _Insecta_,
and _Amphipoda_ and _Isopoda_ over the higher _Crustacea_; Cetaceans and
Seals over the _Primates_; the civilization of the Esquimaux over that
of the European.

"5. Pelzeln has also objected that if the later organisms have
proceeded from the earlier, the whole developmental series, from
the simplest to the highest, could not now exist; in such a case
the simpler organisms must have disappeared."

To this Professor Koelliker replies, with perfect justice, that the
conclusion drawn by Pelzeln does not really follow from Darwin's
premises, and that, if we take the facts of Palaeontology as they stand,
they rather support than oppose Darwin's theory.

"6. Great weight must be attached to the objection brought forward
by Huxley, otherwise a warm supporter of Darwin's hypothesis, that
we know of no varieties which are sterile with one another, as is
the rule among sharply distinguished animal forms.

"If Darwin is right, it must be demonstrated that forms may be
produced by selection, which, like the present sharply
distinguished animal forms, are infertile when coupled with one
another, and this has not been done."