ations arise among its members, and as
these variations are transmitted like any others, new races may be
developed out of the pre-existing ones _ad infinitum_, or, at least,
within any limit at present determined. Given sufficient time and
sufficiently careful selection, and the multitude of races which may
arise from a common stock is as astonishing as are the extreme
structural differences which they may present. A remarkable example of
this is to be found in the rock-pigeon, which Mr. Darwin has, in our
opinion, satisfactorily demonstrated to be the progenitor of all our
domestic pigeons, of which there are certainly more than a hundred
well-marked races. The most noteworthy of these races are, the four
great stocks known to the "fancy" as tumblers, pouters, carriers, and
fantails; birds which not only differ most singularly in size, colour,
and habits, but in the form of the beak and of the skull: in the
proportions of the beak to the skull; in the number of tail-feathers; in
the absolute and relative size of the feet; in the presence or absence
of the uropygial gland; in the number of vertebrae in the back; in short,
in precisely those characters in which the genera and species of birds
differ from one another.

And it is most remarkable and instructive to observe, that none of these
races can be shown to have been originated by the action of changes in
what are commonly called external circumstances, upon the wild
rock-pigeon. On the contrary, from time immemorial, pigeon fanciers have
had essentially similar methods of treating their pets, which have been
housed, fed, protected and cared for in much the same way in all
pigeonries. In fact, there is no case better adapted than that of the
pigeons, to refute the doctrine which one sees put forth on high
authority, that "no other characters than those founded on the
development of bone for the attachment of muscles" are capable of
variation. In precise contradiction of this hasty assertion, Mr.
Darwin's researches prove that the skeleton of the wings in domestic
pigeons has hardly varied at all from that of the wild type; while, on
the other hand, it is in exactly those respects, such as the relative
length of the beak and skull, the number of the vertebrae, and the number
of the tail-feathers, in which muscular exertion can have no important
influence, that the utmost amount of variation has taken place.

We have said that the following out of the properties ex