on the other hand, an internal activity is appealed to, then it must
be something quite different from what we usually call an effort, for
never has an effort been known to produce the slightest complication of
an organ, and yet an enormous number of complications, all admirably
coordinated, have been necessary to pass from the pigment-spot of the
Infusorian to the eye of the vertebrate. But, even if we accept this
notion of the evolutionary process in the case of animals, how can we
apply it to plants? Here, variations of form do not seem to imply, nor
always to lead to, functional changes; and even if the cause of the
variation is of a psychological nature, we can hardly call it an effort,
unless we give a very unusual extension to the meaning of the word. The
truth is, it is necessary to dig beneath the effort itself and look for
a deeper cause.

This is especially necessary, we believe, if we wish to get at a cause
of regular hereditary variations. We are not going to enter here into
the controversies over the transmissibility of acquired characters;
still less do we wish to take too definite a side on this question,
which is not within our province. But we cannot remain completely
indifferent to it. Nowhere is it clearer that philosophers can not
to-day content themselves with vague generalities, but must follow the
scientists in experimental detail and discuss the results with them. If
Spencer had begun by putting to himself the question of the
hereditability of acquired characters, his evolutionism would no doubt
have taken an altogether different form. If (as seems probable to us) a
habit contracted by the individual were transmitted to its descendants
only in very exceptional cases, all the Spencerian psychology would need
remaking, and a large part of Spencer's philosophy would fall to pieces.
Let us say, then, how the problem seems to us to present itself, and in
what direction an attempt might be made to solve it.

After having been affirmed as a dogma, the transmissibility of acquired
characters has been no less dogmatically denied, for reasons drawn _a
priori_ from the supposed nature of germinal cells. It is well known how
Weismann was led, by his hypothesis of the continuity of the germ-plasm,
to regard the germinal cells--ova and spermatozoa--as almost independent
of the somatic cells. Starting from this, it has been claimed, and is
still claimed by many, that the hereditary transmission of an acquired