life; as when an hereditary disease, which appears in old age alone,
has been communicated to the offspring from the reproductive element of
one parent. Or again, as when the horns of cross-bred cattle have been
affected by the shape of the horns of either parent. For the welfare of
a very young animal, as long as it remains in its mother s womb, or in
the egg, or as long as it is nourished and protected by its parent, it
must be quite unimportant whether most of its characters are fully
acquired a little earlier or later in life. It would not signify, for
instance, to a bird which obtained its food best by having a long beak,
whether or not it assumed a beak of this particular length, as long as
it was fed by its parents. Hence, I conclude, that it is quite
possible, that each of the many successive modifications, by which each
species has acquired its present structure, may have supervened at a
not very early period of life; and some direct evidence from our
domestic animals supports this view. But in other cases it is quite
possible that each successive modification, or most of them, may have
appeared at an extremely early period.
I have stated in the first chapter, that there is some evidence to
render it probable, 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 horns of almost full-grown cattle.
But further than this, variations which, for all that we can see, might
have appeared earlier or later in life, tend to appear at a
corresponding age in the offspring and parent. I am far from meaning
that this is invariably the case; and I could give a good many 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, if their truth be admitted, will, I believe,
explain all the above specified leading facts in embryology. But first
let us look at a few analogous cases in domestic varieties. Some
authors who have written on Dogs, maintain that the greyhound and
bulldog, though appearing so different, are really varieties most
closely allied, and have probably 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
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