Even in this case,
however, it would be the exertions, or use and disuse, that would be
the main agents in the modification. But it is not often that Mr.
Wallace thus backslides. His present position is that acquired (as
distinguished from congenital) modifications are not inherited at
all. He does not indeed put his faith prominently forward and pin
himself to it as plainly as could be wished, but under the heading,
"The Non-Heredity of Acquired Characters," he writes as follows on
p. 440 of his recent work in reference to Professor Weismann's
Theory of Heredity:-
"Certain observations on the embryology of the lower animals are
held to afford direct proof of this theory of heredity, but they are
too technical to be made clear to ordinary readers. A logical
result of the theory is the impossibility of the transmission of
acquired characters, since the molecular structure of the germ-plasm
is already determined within the embryo; and Weismann holds that
there are no facts which really prove that acquired characters can
be inherited, although their inheritance has, by most writers, been
considered so probable as hardly to stand in need of direct proof.
"We have already seen in the earlier part of this chapter that many
instances of change, imputed to the inheritance of acquired
variations, are really cases of selection.
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