originated as a mutation, because the term mutation means a new character
which develops in the soma as a result of the loss or gain of some factor
or determinant in the chromosomes. To say that certain mutations consist
of new factors which only the development of characters in the soma when
the part of the soma concerned is stimulated by a hormone, is a mere
assertion unsupported at present by any evidence. As an example of the way
in which Mendelians misunderstand the problem to be considered, I may
refer to Doncaster's book, _The Determination of Sex_ [Footnote: Camb.
Univ. 1914, p. 99.] in which he remarks: 'It follows that the secondary
sexual characters cannot arise simply from the action of hormones; they
must be due to differences in the tissues of the body, and the activity of
the ovary or testis must be regarded rather as a stimulus to their
development than as their source of origin.' This seems to imply a serious
misunderstanding of the idea of the action of the hormones from the gonads
and of hormones in general. No one would suggest that the hormones from
the testis should be regarded as in any sense the origin of the antlers of
a stag. If so, why should not antlers equally develop in the stallion or
in the buck rabbit, or indeed in man? How far Doncaster is right in
holding that the soma is different in the two sexes is a question already
mentioned, but it is obvious that in each individual the somatic sexual
characters proper to its species are present potentially in its
constitution by heredity--in other words, as factors or determinants in
the chromosomes of the zygote from which it was developed; but the normal
development of such characters in the individual soma is either entirely
dependent on the stimulus of the hormone of the gonad or is profoundly
influenced by the presence or absence of that stimulus. The evidence, as
we have seen, proves that, at any rate in the large number of cases where
this relation between somatic sex-characters and hormones produced by the
reproductive organs exists, the characters are inherited by both sexes. In
one sex they are fully developed, in the other rudimentary or wanting. But