The more important and best-known phenomena of heredity do not require
any such hypothesis, and leading facts (such as atavism, transmission of
lost parts, and the general non-transmission of acquired characters) are
so adverse to it that Darwin has to concede that many of the
reproductive gemmules are atavistic, and that by continuous
self-multiplication they may preserve a practical "continuity of
germ-substance," as Weismann would term it. The idea that the
relationship of offspring to parent is one of direct descent is, as
Galton tells us, "wholly untenable"; and the only reason he admits some
supplementary traces of pangenesis into his "Theory of Heredity,"[71] is
that he may thus account for the more or less questionable cases of the
transmission of acquired characters. But there appears to be no
necessity even for this concession. We ought therefore to dispense with
the useless and gratuitous hypothesis that cells multiply by throwing
off minute self-multiplying gemmules, as well as by the well-known
method of self-division. If pangenesis occurs, the transmission of
acquired characters ought to be a prominent fact. The size, strength,
health and other good or evil qualities of the cells could hardly fail
to exercise a marked and corresponding effect upon the size and quality
of the reproductive gemmules thrown off by those cells. The direct
evidence tends to show that these free gemmules do not exist.
Transfusion of blood has failed to affect inheritance in the slightest
degree. Pangenesis, with its attraction of gemmules from all parts of
the body into the germ-cells, and the free circulation of gemmules in
the offspring till they hit upon or are attracted by the particular cell
or cells, with which alone they can readily unite, seems a less feasible
theory and less in conformity with the whole of the facts than an
hypothesis of germ-continuity which supposes that the development of the
germ-plasm and of the successive self-dividing cells of the body
proceeds from within. Darwin's keen analogy of the fertilization of
plants by pollen renders development from without conceivable, but as
there are no insects to convey gemmules to their destination, each kind
of gemmule would have to be exceedingly numerous and easily attracted
from amongst an inconceivable number of other gemmules. Arguments
against pangenesis can also be drawn from the case of neuter insects--a
fact which seems to have escaped Darwin's notice, although he had seen
how strongly that case was opposed to the doctrine which is the
essential basis of the theory of pangenesis.