nt of proportional difference.

As the evidence appears to me conclusive, that the several domestic
breeds of Pigeon have descended from one wild species, I compared young
pigeons of various breeds, within twelve hours after being hatched; I
carefully measured the proportions (but will not here give details) of
the beak, width of mouth, length of nostril and of eyelid, size of
feet and length of leg, in the wild stock, in pouters, fantails, runts,
barbs, dragons, carriers, and tumblers. Now some of these birds, when
mature, differ so extraordinarily in length and form of beak, that
they would, I cannot doubt, be ranked in distinct genera, had they been
natural productions. But when the nestling birds of these several breeds
were placed in a row, though most of them could be distinguished from
each other, yet their proportional differences in the above specified
several points were incomparably less than in the full-grown birds. Some
characteristic points of difference--for instance, that of the width
of mouth--could hardly be detected in the young. But there was one
remarkable exception to this rule, for the young of the short-faced
tumbler differed from the young of the wild rock-pigeon and of the other
breeds, in all its proportions, almost exactly as much as in the adult
state.

The two principles above given seem to me to explain these facts in
regard to the later embryonic stages of our domestic varieties. Fanciers
select their horses, dogs, and pigeons, for breeding, when they are
nearly grown up: they are indifferent whether the desired qualities
and structures have been acquired earlier or later in life, if the
full-grown animal possesses them. And the cases just given, more
especially that of pigeons, seem to show that the characteristic
differences which give value to each breed, and which have been
accumulated by man's selection, have not generally first appeared at
an early period of life, and have been inherited by the offspring at a
corresponding not early period. But the case of the short-faced tumbler,
which when twelve hours old had acquired its proper proportions,
proves that this is not the universal rule; for here the characteristic
differences must either have appeared at an earlier period than usual,
or, if not so, the differences must have been inherited, not at the
corresponding, but at an earlier age.

Now let us apply these facts and the above two principles--which latter,
though not proved