of the various points in which their organization differs. In the
first place, the back of the skull may differ a good deal, and the
development of the bones of the face may vary a great deal; the back
varies a good deal; the shape of the lower jaw varies; the tongue
varies very greatly, not only in correlation to the length and size of
the beak, but it seems also to have a kind of independent variation of
its own. Then the amount of naked skin round the eyes, and at the base
of the beak, may vary enormously; so may the length of the eyelids, the
shape of the nostrils, and the length of the neck. I have already
noticed the habit of blowing out the gullet, so remarkable in the
Pouter, and comparatively so in the others. There are great
differences, too, in the size of the female and the male, the shape of
the body, the number and width of the processes of the ribs, the
development of the ribs, and the size, shape, and development of the
breastbone. We may notice, too,--and I mention the fact because it has
been disputed by what is assumed to be high authority,--the variation
in the number of the sacral vertebrae. The number of these varies from
eleven to fourteen, and that without any diminution in the number of
the vertebrae of the back or of the tail. Then the number and position
of the tail-feathers may vary enormously, and so may the number of the
primary and secondary feathers of the wings. Again, the length of the
feet and of the beak,--although they have no relation to each other,
yet appear to go together,--that is, you have a long beak wherever you
have long feet. There are differences also in the periods of the
acquirement of the perfect plumage,--the size and shape of the
eggs,--the nature of flight, and the powers of flight,--so-called
"homing" birds having enormous flying powers;* while, on the other
hand, the little Tumbler is so called because of its extraordinary
faculty of turning head over heels in the air, instead of pursuing a
direct course. And, lastly, the dispositions and voices of the birds