e geographical distribution of organisms--it will be necessary to return
somewhat to the subject of the independent origin of closely similar forms,
in regard to which some additional remarks will be found towards the end of
the seventh chapter.

In this third chapter an effort has been made to show that while on the
Darwinian theory concordant variations are extremely improbable, yet Nature
presents us with abundant examples of such; the most striking of which are,
perhaps, the higher organs of sense. Also that an important influence is
exercised by conditions connected with geographical distribution, but that
a deeper-seated influence is at work, which is hinted at by those special
tendencies in definite directions, which are the properties of certain
groups. Finally, that these facts, when taken together, afford strong
evidence that "Natural Selection" has not been the exclusive or predominant
cause of the various organic structural peculiarities. This conclusion has
also been re-enforced by the consideration of phenomena presented to us by
the inorganic world. [Page 97]

* * * * *

CHAPTER IV.

MINUTE AND GRADUAL MODIFICATIONS.

There are difficulties as to minute modifications, even if not
fortuitous.--Examples of sudden and considerable modifications of
different kinds.--Professor Owen's view.--Mr. Wallace.--Professor
Huxley.--Objections to sudden
changes.--Labyrinthodont.--Potto.--Cetacea.--As to origin of bird's
wing.--Tendrils of climbing plants.--Animals once supposed to be
connecting links.--Early specialization of
structure.--Macrauchenia.--Glyptodon.--Sabre-toothed
tiger.--Conclusion.

Not only are there good reasons against the acceptance of the exclusive
operation of "Natural Selection" as the one means of specific origination,
but there are difficulties in the way of accounting for such origination by
the sole action of modifications which are infinitesimal and minute,
whether fortuitous or not.

Arguments may yet be advanced in favour of the view that new species have
from time to time manifested themselves with suddenness, and by
modifications appearing at once (as great in degree as are those which
separate _Hipparion_ from _Equus_), the species remaining stable in the
intervals of such modifications: by stable being meant that their
variations only extend for a certain degree in various directions, like
oscillations in a st