permanent variety. But characters exclusively due to analogous variation
would probably be of an unimportant nature, for the preservation of
all functionally important characters will have been determined through
natural selection, in accordance with the different habits of the
species. It might further be expected that the species of the same
genus would occasionally exhibit reversions to long-lost characters.
As, however, we do not know the common ancestor of any natural group,
we cannot distinguish between reversionary and analogous characters.
If, for instance, we did not know that the parent rock-pigeon was not
feather-footed or turn-crowned, we could not have told, whether such
characters in our domestic breeds were reversions or only analogous
variations; but we might have inferred that the blue colour was a case
of reversion from the number of the markings, which are correlated with
this tint, and which would not probably have all appeared together from
simple variation. More especially we might have inferred this from the
blue colour and the several marks so often appearing when differently
coloured breeds are crossed. Hence, although under nature it must
generally be left doubtful, what cases are reversions to formerly
existing characters, and what are new but analogous variations, yet
we ought, on our theory, sometimes to find the varying offspring of a
species assuming characters which are already present in other members
of the same group. And this undoubtedly is the case.

The difficulty in distinguishing variable species is largely due to
the varieties mocking, as it were, other species of the same genus.
A considerable catalogue, also, could be given of forms intermediate
between two other forms, which themselves can only doubtfully be ranked
as species; and this shows, unless all these closely allied forms be
considered as independently created species, that they have in varying
assumed some of the characters of the others. But the best evidence of
analogous variations is afforded by parts or organs which are generally
constant in character, but which occasionally vary so as to resemble,
in some degree, the same part or organ in an allied species. I have
collected a long list of such cases; but here, as before, I lie under
the great disadvantage of not being able to give them. I can only repeat
that such cases certainly occur, and seem to me very remarkable.

I will, however, give one curious and comp