maintain the normal condition of the antlers. Simmonds, [Footnote:
_Fortschr. a. d. G. d. Roentgenstr._, xiv., 1909-10.] however, found that
isolated seminal tubules remained, and regeneration took place, and
concludes that both spermatic cells and interstitial cells take part in
producing the testis hormone. The conclusions of two other investigators
have an important bearing on this question--namely, that of Miss Boring
[Footnote: _Biol. Bull._, xxiii. 1912.] that there is no interstitial
tissue in the bird's testis, and that of Miss Lane-Claypon, [Footnote:
_Proc. Roy. Soc._, 1905] that the interstitial cells of the ovary arise
from the germinal epithelium, and are perfectly equipotential with those
which form the ova and Graafian follicles. It seems possible, although no
such suggestion has been made, that the interstitial cells might either
normally or exceptionally give rise to ova and spermatocytes. The
observations of Seligmann and Shattock on the relation of spermatogenesis
to the development of nuptial plumage in drakes probably receive their
explanation from the above facts. Spermatogenesis is not the only source
of the testicular hormone: changes in the secretory activity of the
interstitial cells or spermatocytes are sufficient to account for periodic
development of somatic sex-characters, and the same reasoning applies to
the antlers of stags.

THE MAMMARY OR MILK GLANDS

The milk glands in Mammals constitute one of the most remarkable of
secondary sexual characters. Except in their functional relations to the
primary organs, the ovaries, and to the uterus, there is nothing sexual
about them. They are parts of the skin, being nothing more or less than
enormous enlargements of dermal glands, either sebaceous or sudoriparous.
Uterine and mammary functions are generally regarded as essentially female
characteristics, and are included in the popular idea of the sex of woman.