cause acting on both; but when amongst individuals, apparently exposed
to the same conditions, any very rare deviation, due to some
extraordinary combination of circumstances, appears in the parent say,
once amongst several million individuals and it reappears in the child,
the mere doctrine of chances almost compels us to attribute its
reappearance to inheritance. Every one must have heard of cases of
albinism, prickly skin, hairy bodies, etc., appearing in several
members of the same family. If strange and rare deviations of structure
are truly inherited, less strange and commoner deviations may be freely
admitted to be inheritable. Perhaps the correct way of viewing the
whole subject, would be, to look at the inheritance of every character
whatever as the rule, and non-inheritance as the anomaly.
The laws governing inheritance are quite unknown; no one can say why
the same peculiarity in different individuals of the same species, and
in individuals of different species, is sometimes inherited and
sometimes not so; why the child often reverts in certain characters to
its grandfather or grandmother or other much more remote ancestor; why
a peculiarity is often transmitted from one sex to both sexes or to one
sex alone, more commonly but not exclusively to the like sex. It is a
fact of some little importance to us, that peculiarities appearing in
the males of our domestic breeds are often transmitted either
exclusively, or in a much greater degree, to males alone. A much more
important rule, which I think may be trusted, is that, at whatever
period of life a peculiarity first appears, it tends to appear in the
offspring at a corresponding age, though sometimes earlier. In many
cases this could
not be otherwise: thus the inherited peculiarities in the horns of
cattle could appear only in the offspring when nearly mature;
peculiarities in the silkworm are known to appear at the corresponding
caterpillar or cocoon stage. But hereditary diseases and some other
facts make me believe that the rule has a wider extension, and that
when there is no apparent reason why a peculiarity should appear at any
particular age, yet that it does tend to appear in the offspring at the
same period at which it first appeared in the parent. I believe this
rule to be of the highest importance in explaining the laws of
embryology. These remarks are of course confined to the first
_appearance_ of the peculiarity, and not to its primary cause, which
may have acted on the ovules or male element; in nearly the same manner
as in the crossed offspring from a short-horned cow by a long-horned
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