cquired a little earlier or later in life. It would not signify,
for instance, to a bird which obtained its food by having a much-curved
beak whether or not while young it possessed a beak of this shape, as
long as it was fed by its parents.

I have stated in the first chapter, that at whatever age any variation
first appears in the parent, it tends to reappear at a corresponding age
in the offspring. Certain variations can only appear at corresponding
ages; for instance, peculiarities in the caterpillar, cocoon, or imago
states of the silk-moth; or, again, in the full-grown horns of cattle.
But variations which, for all that we can see might have appeared either
earlier or later in life, likewise tend to reappear at a corresponding
age in the offspring and parent. I am far from meaning that this is
invariably the case, and I could give several exceptional cases of
variations (taking the word in the largest sense) which have supervened
at an earlier age in the child than in the parent.

These two principles, namely, that slight variations generally appear
at a not very early period of life, and are inherited at a corresponding
not early period, explain, as I believe, all the above specified leading
facts in embryology. But first let us look to a few analogous cases in
our domestic varieties. Some authors who have written on Dogs maintain
that the greyhound and bull-dog, though so different, are really closely
allied varieties, descended from the same wild stock, hence I was
curious to see how far their puppies differed from each other. I was
told by breeders that they differed just as much as their parents, and
this, judging by the eye, seemed almost to be the case; but on actually
measuring the old dogs and their six-days-old puppies, I found that
the puppies had not acquired nearly their full amount of proportional
difference. So, again, I was told that the foals of cart and
race-horses--breeds which have been almost wholly formed by selection
under domestication--differed as much as the full-grown animals; but
having had careful measurements made of the dams and of three-days-old
colts of race and heavy cart-horses, I find that this is by no means the
case.

As we have conclusive evidence that the breeds of the Pigeon are
descended from a single wild species, I compared the young pigeons
within twelve hours after being hatched. I carefully measured the
proportions (but will not here give the details) of the beak, w