all organisms, as we shall presently see, the cells or
organic units of the embryo during the successive stages of development may
in like manner be said to be fertilised by the gemmules of the cells, which
come next in the order of formation.

Animals, when capable of sexual reproduction, are fully developed, and it
is scarcely possible that the male element should affect the tissues of the
mother in the same direct manner as with plants; nevertheless it is certain
that her ovaria are sometimes affected by a previous impregnation, so that
the ovules subsequently fertilised by a distinct male are plainly
influenced in character; and this, as in the case of foreign pollen, is
intelligible through the diffusion, retention, and action of the gemmules
included within the spermatozoa of the previous male.

Each organism reaches maturity through a longer or shorter course of
development. The changes may be small and insensibly slow, as when a child
grows into a man, or many, abrupt, and slight, as in the metamorphoses of
certain ephemerous insects, or again few and strongly marked, as with most
other insects. Each part may be moulded within a previously existing and
corresponding part, and in this case it will appear, falsely as I believe,
to be formed from the old part; or it may be developed within a wholly
distinct part of the body, as in the extreme cases of metagenesis. An eye,
for instance, may be developed at a spot where no eye previously existed.
We have also seen that allied organic beings in the course of their
metamorphoses sometimes attain nearly the same structure after passing
{389} through widely different forms; or conversely, after passing through
nearly the same early forms, arrive at a widely different termination. In
these cases it is very difficult to believe that the early cells or units
possess the inherent power, independently of any external agent, of
producing new structures wholly different in form, position, and function.
But these cases become plain on the hypothesis of pangenesis. The organic
units, during each stage of development, throw off gemmules, which,
multiplying, are transmitted to the offspring. In the offspring, as soon as
any particular cell or unit in the proper order of development becomes
partially developed, it unites with (or to speak metaphorically is
fertilised by) the gemmule of the next succeeding cell, and so onwards.
Now, supposing that at any stage of development, certain