note the fact, that after increased use, alternated with times of
repose, there accrues to the organ in all animal economy an increased
power of execution with an increased power of assimilation and a gain
in size.

This gain in size consists not only in the enlargement of the
individual cells or fibres of which the organ is composed, but in the
multiplication of their number; for when cells have grown to a
certain size they give rise to others, which inherit more or less
completely the qualities of those from which they came, and therefore
appear to be repetitions of the same cell. This growth, and
multiplication of cells is only a special phase of those manifold
functions which characterise organised matter, and which consist not
only in what goes on within the cell substance as alterations or
undulatory movement of the molecular disposition, but also in that
which becomes visible outside the cells as change of shape,
enlargement, or subdivision. Reproduction of performance, therefore,
manifests itself to us as reproduction of the cells themselves, as
may be seen most plainly in the case of plants, whose chief work
consists in growth, whereas with animal organism other faculties
greatly preponderate.

Let us now take a brief survey of a class of facts in the case of
which we may most abundantly observe the power of memory in organised
matter. We have ample evidence of the fact that characteristics of
an organism may descend to offspring which the organism did not
inherit, but which it acquired owing to the special circumstances
under which it lived; and that, in consequence, every organism
imparts to the germ that issues from it a small heritage of
acquisitions which it has added during its own lifetime to the gross