dfruit, and others previously mentioned, have their
reproductive organs so seriously affected as to be generally quite
sterile; and when they do yield seed, the seedlings, judging from the
large number of cultivated races which exist, must be variable in an
extreme degree. These facts indicate that there is some relation
between the state of the reproductive organs and a tendency to
variability; but we must not conclude that the relation is strict.
Although many of our highly cultivated plants may have their pollen in
a deteriorated condition, yet, as we have previously seen, they yield
more seed, and our anciently domesticated animals are more prolific,
than the corresponding species in a state of nature. The peacock is
almost the only bird which is believed to be less fertile under
domestication than in its native state, and it has varied in a
remarkably small degree. From these considerations it would seem that
changes in the conditions of life lead either to sterility or to
variability, or to both; and not that sterility induces variability. On
the whole it is probable that any cause affecting the organs of
reproduction would likewise affect their product,--that is, the
offspring thus generated.

{269}

The period of life at which the causes that induce variability act, is
another obscure subject, which has been discussed by various
authors.[651] In some of the cases, to be given in the following
chapter, of modifications from the direct action of changed conditions,
which are inherited, there can be no doubt that the causes have acted
on the mature or nearly mature animal. On the other hand,
monstrosities, which cannot be distinctly separated from lesser
variations, are often caused by the embryo being injured whilst in the
mother's womb or in the egg. Thus I. Geoffroy St. Hilaire[652] asserts
that poor women who work hard during their pregnancy, and the mothers
of illegitimate children troubled in their minds and forced to conceal
their state, are far more liable to give birth to monsters than women
in easy circumstances. The eggs of the fowl when placed upright or
otherwise treated unnaturally frequently produce monstrous chickens. It
would, however, appear that complex monstrosities are induced more
frequently during a rather late than during a very early period of
embr