h and number of the ribs, the presence of processes, the number of
the sacral vertebrae, and the length of the sternum, all vary. The number
and size of the coccygeal vertebrae vary, apparently in correlation with the
increased size of the tail. The size and shape of the perforations in the
sternum, and the size and divergence of the arms of the furcula, differ.
The oil-gland varies in development, and is sometimes quite aborted. The
direction and length of certain feathers have been much modified, as in the
hood of the Jacobin and the frill of the Turbit. The wing and tail feathers
generally vary in {178} length together, but sometimes independently of
each other and of the size of the body. The number and position of the
tail-feathers vary to an unparalleled degree. The primary and secondary
wing-feathers occasionally vary in number, apparently in correlation with
the length of the wing. The length of the leg and the size of the feet,
and, in connection with the latter, the number of the scutellae, all vary. A
web of skin sometimes connects the bases of the two inner toes, and almost
invariably the two outer toes when the feet are feathered.

The size of the body differs greatly: a runt has been known to weigh more
than five times as much as a short-faced tumbler. The eggs differ in size
and shape. According to Parmentier,[314] some races use much straw in
building their nests, and others use little; but I cannot hear of any
recent corroboration of this statement. The length of time required for
hatching the eggs is uniform in all the breeds. The period at which the
characteristic plumage of some breeds is acquired, and at which certain
changes of colour supervene, differs. The degree to which the young birds
are clothed with down when first hatched is different, and is correlated in
a singular manner with the future colour of the plumage. The manner of
flight, and certain inherited movements, such as clapping the wings,
tumbling either in the air or on the ground, and the manner of courting the
female, present the most singular differences. In disposition the several
races differ. Some races are very silent; others coo in a highly peculiar
manner.

Although many different races have kept true in character during several
centuries, as we shall hereafter more fully see, yet there is far more
individual variability in the truest breeds than in birds in a state of
nature. There is hardly any exception to the rule that tho