is apparently due to the sexual system being easily affected by
changed conditions, so that it is often rendered impotent; and when not so
seriously affected, it often fails in its proper function of transmitting
truly the characters of the parents to the offspring. But variability is
not necessarily connected with the sexual system, as we see from the cases
of bud-variation; and although we may not be able to trace the nature of
the connexion, it is probable that many deviations of structure which
appear in sexual offspring result from changed conditions acting directly
on the organisation, independently of the reproductive organs. In some
instances we may feel sure of this, when all, or nearly all the individuals
which have been similarly exposed are similarly and definitely affected--as
in the dwarfed and otherwise changed maize brought from hot countries when
cultivated in Germany; in the change of the fleece in sheep within the
tropics; to a certain extent in the increased size and early maturity of
our highly-improved domesticated animals; in inherited gout from
intemperance; and in many other such cases. Now, as such changed conditions
do not especially affect the reproductive organs, it seems mysterious on
any ordinary view why their product, the new organic being, should be
similarly affected.

How, again, can we explain to ourselves the inherited effects of the use or
disuse of particular organs? The domesticated duck flies less and walks
more than the wild duck, and its limb-bones have become in a corresponding
manner diminished and increased in comparison with those of the wild duck.
A horse is trained to certain paces, and the colt inherits similar
consensual movements. The domesticated rabbit becomes tame from close
confinement; the dog intelligent from associating with man; the retriever
is taught to fetch and carry: and these {372} mental endowments and bodily
powers are all inherited. Nothing in the whole circuit of physiology is
more wonderful. How can the use or disuse of a particular limb or of the
brain affect a small aggregate of reproductive cells, seated in a distant
part of the body, in such a manner that the being developed from these
cells inherits the characters of either one or both parents? Even an
imperfect answer to this question would be satisfactory.

Sexual reproduction does not essentially differ, as we have seen, from
budding or self-division, and these processes graduate through the