had thus
become perceptibly shortened, fanciers would almost certainly strive to
reduce it still more by the continued selection of birds with the shortest
beaks; whilst at the same time other fanciers, as we know has actually been
the case, would, in other sub-breeds, strive to increase its length. With
the increased length of the beak, the tongue would become greatly
lengthened, as would the eyelids with the increased development {219} of
the eye-wattles; with the reduced or increased size of the feet the number
of the scutellae would vary; with the length of the wing the number of the
primary wing-feathers would differ; and with the increased length of the
body in the pouter the number of the sacral vertebrae would be augmented.
These important and correlated differences of structure do not invariably
characterise any breed; but if they had been attended to and selected with
as much care as the more conspicuous external differences, there can hardly
be a doubt that they would have been rendered constant. Fanciers could
assuredly have made a race of tumblers with nine instead of ten primary
wing-feathers, seeing how often the number nine appears without any wish on
their part, and indeed in the case of the white-winged varieties in
opposition to their wish. In a similar manner, if the vertebrae had been
visible and had been attended to by fanciers, assuredly an additional
number might easily have been fixed in the pouter. If these latter
characters had once been rendered constant we should never have suspected
that they had at first been highly variable, or that they had arisen from
correlation, in the one case with the shortness of the wings, and in the
other case with the length of the body.

In order to understand how the chief domestic races have become distinctly
separated from each other, it is important to bear in mind, that fanciers
constantly try to breed from the best birds, and consequently that those
which are inferior in the requisite qualities are in each generation
neglected; so that after a time the less improved parent-stocks and many
subsequently formed intermediate grades become extinct. This has occurred
in the case of the pouter, turbit, and trumpeter, for these highly improved
breeds are now left without any links closely connecting them either with
each other or with the aboriginal rock-pigeon. In other countries, indeed,
where the same care has not been applied, or where the same fashion has not