aborted. Several other less distinct breeds might be specified.

In the skeletons of the several breeds, the development of the bones of the
face, in length and breadth and curvature, differs enormously. The shape,
as well as the breadth and length of the ramus of the lower jaw, varies in
a highly remarkable manner. The caudal and sacral vertebrae vary in
number; as does the number of the ribs, together with their relative
breadth and the presence of processes. The size and shape of the apertures
in the sternum are highly variable; so is the degree of divergence and
relative size of the two arms of the furcula. The proportional width of
the gape of mouth, the proportional length of the eyelids, of the orifice
of the nostrils, of the tongue (not always in strict correlation with the
length of beak), the size of the crop and of the upper part of the
oesophagus; the development and abortion of the oil-gland; the number of
the primary wing and caudal feathers; the relative length of the wing and
tail to each other and to the body; the relative length of the leg and
foot; the number of scutellae on the toes, the development of skin between
the toes, are all points of structure which are variable. The period at
which the perfect plumage is acquired varies, as does the state of the down
with which the nestling birds are clothed when hatched. The shape and size
of the eggs vary. The manner of flight, and in some breeds the voice and
disposition, differ remarkably. Lastly, in certain breeds, the males and
females have come to differ in a slight degree from each other.

Altogether at least a score of pigeons might be chosen, which, if shown to
an ornithologist, and he were told that they were wild birds, would
certainly be ranked by him as well-defined species. Moreover, I do not
believe that any ornithologist would in this case place the English
carrier, the short-faced tumbler, the runt, the barb, pouter, and fantail
in the same genus; more especially as in each of these breeds several