say why the same peculiarity in different individuals of the same species,
or in different species, is sometimes inherited and sometimes not so; why
the child often reverts in certain characteristics to its grandfather or
grandmother or 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 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 the 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
reappear 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 silk-worm 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 the primary cause which may have acted on the
ovules or on the male element; in nearly the same manner as the increased
length of the horns in the offspring from a short-horned cow by a
long-horned bull, though appearing late in life, is clearly due to the male
element.

Having alluded to the subject of reversion, I may here refer to a statement
often made by naturalists--namely, that our domestic varieties, when run
wild, gradually but invariably revert in character to their aboriginal