different muscles of the hand and arm.
How can this use of special muscles stamp itself upon the germ-cells
in such a way that the offspring will have these special muscles
enlarged? Granting that external influences of environment and
bodily condition may effect the germ-cells; granting even that some
of the most general effects of use and disuse might be transmitted,
what warrant have we for believing that the special acquired
characteristic can be transmitted? Weismann answers, None at all.
The somatoplasm can only in the most general way affect the
self-perpetuating, close corporation of the germ-plasm.[A]

[Footnote A: Weismann, Essays, p. 286.]

There is thus, according to Weismann, nothing to direct variation to
certain organs, or to guide and combine the variations of these
organs along certain lines, except natural selection. To a certain
extent variation may be limited by the very structure of the animal.
But within these limits there are wide ranges where one variation is
apparently just as likely to occur as another.

Within these wide limits variation appears to be fortuitous. Natural
selection must wait until the individuals appear in which these
variations occur already correlated, and then seize upon these
individuals. It is apparently the only guiding, directing force.
Linear variation, that is, a variation advancing continuously along
one or very few straight lines, would appear to be impossible.

In Naegeli's theory initial tendency is overwhelmingly dominant; in
Weismann's, natural selection is almighty.

Weismann's followers have received the name of Neo-Darwinians. The
so-called Neo-Lamarckian school believes in the transmissibility of
acquired characteristics, and of at least particular effects of use
and disuse. The one theory is neither more nor less Darwinian than
the other. For while Darwin emphasized natural selection, he
accepted to a certain extent the transmission of special effects of
use and disuse.

A special theory of heredity, pangenesis, has been accepted by many
of the Neo-Lamarckian school. The theory of pangenesis, as
propounded by Mr. Darwin, may be very briefly stated as follows: The
cells in all parts of the body are continually throwing off germinal
particles, or "gemmules." These become scattered through the body,
grow, and multiply by division. On account of mutual attraction they
unite in the reproductive glands to form eggs or spermatozoa. The
germ-cells are thu