elves have undergone no modification; but the mutations in
the above respects will amply account for much fluctuating {397}
variability. Secondly, in the cases in which the organisation has been
modified by changed conditions, the increased use or disuse of parts, or
any other cause, the gemmules cast off from the modified units of the body
will be themselves modified, and, when sufficiently multiplied, will be
developed into new and changed structures.

* * * * *

Turning now to Inheritance: if we suppose a homogeneous gelatinous
protozoon to vary and assume a reddish colour, a minute separated atom we
aid naturally, as it grew to full size, retain the same colour; and we
should have the simplest form of inheritance.[926] Precisely the same view
may be extended to the infinitely numerous and diversified units of which
the whole body in one of the higher animals is composed; and the separated
atoms are our gemmules. We have already sufficiently discussed the
inheritance of the direct effects of changed conditions, and of increased
use or disuse of parts, and, by implication, the important principle of
inheritance at corresponding ages. These groups of facts are to a large
extent intelligible on the hypothesis of pangenesis, and on no other
hypothesis as yet advanced.

A few words must be added on the complete abortion or suppression of
organs. When a part becomes diminished by disuse prolonged during many
generations, the principle of economy of growth, as previously explained,
will tend to reduce it still further; but this will not account for the
complete or almost complete obliteration of, for instance, a minute papilla
of cellular tissue representing a pistil, or of a microscopically minute
nodule of bone representing a tooth. In certain cases of suppression not
yet completed, in which a rudiment occasionally reappears through
reversion, diffused gemmules derived from this part must, according to our
view, still exist; hence we must suppose that the cells, in union with
which the rudiment was formerly developed, in these cases fail in their
affinity for such gemmules. But in the cases of complete and final abortion
the gemmules themselves no doubt have perished; nor is this {398} in any
way improbable, for, though a vast number of active and long-dormant
gemmules are diffused and nourished in each living creature, yet there must
be some limit to their number; and it appears natural th