of one endocrine and less of
another, is at the bottom of the phenomenon of variation, basic for
the origin of new species as well as the extinction of the old. In
short, viewing the internal secretions as determinants, by their
quantitative variations, of a host of biologic phenomena furnishes a
concrete and detailed foundation for Darwin's theory of pangenesis.

INHERITANCE OF ACQUIRED CHARACTERS

Darwin's theory of pangenesis was an attempt to harmonize everything
known in his time about heredity. It supposed that the various
organs of the body gave off into the blood substances, themselves
in miniature, which were taken up by the sex cells, and so became
responsible for the development of their mother-organ in the newly
forming individual. Modern knowledge cannot accept all this as a
whole. But in a modified version, it has become the germ of a theory
of heredity of which J.T. Cunningham, of Oxford, is the chief backer.

Beginning with the traits and qualities which distinguish the sexes,
grouped as the secondary sex characters, he showed that they are
correlated with the special sexual function of the species in which
they occur. These traits appear only when the hormones occur which
are present in one sex and that only when the gonads of that sex are
mature. In some cases they appear only at the period of the year
when reproduction takes place, disappearing again after the breeding
season. Their presence makes certain cells develop in excessive
numbers at a particular spot in the organism (as in the growth of
breasts from a few sweat glands) or causes them to specialize (to make
hair on the face in man, or to grow antlers on the head of a stag).
After castration, the hormones being absent, all these points of
contrast between the sexes fail to appear. So by analogy we may
explain all somatic and psychic differentiation as functions of the
glands of internal secretion. Contemplated from the angle of the
effect of environment upon the endocrines, and a reflected action
upon the germ cells, we may outline a mechanism of the inheritance of
acquired characters at certain times and consequent adaptation. The
cycle of events would be as follows:

1. A state of lability of cells at a point because of increased or
decreased use.

2. An increased or decreased appropriation by them of the hormone
controlling their function.

3. A corresponding increase or decrease in function of the gland of
internal secretion and so