horticulturists. For these men, by their process of selective
accumulation, have empirically proved what immense changes of type may
thus be brought about; and so have verified by anticipation, and in a
most striking manner, the theory of natural selection--which, as now so
fully explained, is nothing more than a theory of cumulative
modifications by means of selective breeding.

So much, then, by way of generalities. But perhaps the proof of natural
selection as an agency of the first importance in the transmutation of
species may be best brought home to us by considering a few of its
applications in detail. I will therefore devote the rest of the present
chapter to considering a few cases of this kind.

There are so many large fields from which such special illustrations may
be supplied, that it is difficult to decide which of them to draw upon.
For instance, the innumerable, always interesting, and often astonishing
adaptations on the part of flowers to the fertilising agency of insects,
has alone given rise to an extensive literature since the time when
Darwin himself was led to investigate the subject by the guidance of his
own theory. The same may be said of the structures and movements of
climbing plants, and in short, of all the other departments of natural
history where the theory of natural selection has led to the study of
the phenomena of adaptation. For in all these cases the theory of
natural selection, which first led to their discovery, still remains the
only scientific theory by which they can be explained. But among all the
possible fields from which evidences of this kind may be drawn, I think
the best is that which may be generically termed defensive colouring. To
this field, therefore, I will restrict myself. But, even so, the cases
to be mentioned are but mere samples taken from different divisions of
this field; and therefore it must be understood at the outset that they
could easily be multiplied a hundred-fold.

_Protective Colouring._

A vast number of animals are rendered more or less inconspicuous by
resembling the colours of the surfaces on which they habitually rest.
Such, for example, are grouse, partridges, rabbits, &c. Moreover, there
are many cases in which, if the needs of the creature be such that it
must habitually frequent surfaces of different colours, it has acquired
the power of changing its colour accordingly--e. g. cuttle-fish,
flat-fish, frogs, chameleons, &c. The physio