ds to
the intelligence of its men the intelligence of its women.

[Footnote 1: Cf. Geddes and Thomson, _The Evolution of Sex_ _passim_.]

[Footnote 2: Havelock Ellis, _Man and Woman_, has brought together
a mass of very valuable material on the question of the somatic and
psychic differences of man and woman, and H. Campbell, in a volume of
much the same scope, _Differences in the Nervous Organization of Man
and Woman_, has given a resume of the theory of Geddes and Thomson,
and suggested its extension to the human species.]

[Footnote 3: C. Duesing, (1) _Die Regulirung des
Geschlechtsverhaeltnisses bei der Vermehrung der Menschen, Thiere und
Pflanzen_. (2) _Das Geschlechtsverhaeltniss der Geburten in Preussen_.]

[Footnote 4: H. Ploss, "Ueber die das Geschlechtsverhaeltniss der
Kinder bedingenden Ursachen," _Monatsschrift fuer Geburtskunde und
Frauenkrankheiten_, Vol. XII, pp. 321-60.]

[Footnote 5: E. Westermarck, _The History of Human Marriage_, pp.
470-83.]

[Footnote 6: Duesing, _Das Geschlechtsverhaeltniss der Geburten in
Preussen_, pp. 29-33.]

[Footnote 7: Duesing, _loc. cit._, pp. 14-19.]

[Footnote 8: H. Ploss, _Das Weib in der Natur- und Voelkerkunde_, 3.
Aufl., Vol. I, p. 419.]

[Footnote 9: Axel Key, "Die Pubertaetsentwickelung und das Verhaeltniss
derselben zu den Krankheitserscheinungen der Schuljugend,"
_Verhandlungen des X. Internationalen Medicinischen Congresses_, 1890,
Vol. I, p. 91.]

[Footnote 10: Ibid., pp. 84-90.]

[Footnote 11: Geddes and Thompson, _loc. cit._, Book I, chap. 4.]

[Footnote 12: Rolph, quoted by Geddes and Thompson, _loc. cit._, Book
I, chap. 4.]

[Footnote 13: Geddes and Thompson, _ibid._]

[Footnote 14: G. Klebs, _Ueber das Verhaeltniss des maennlichen und
weiblichen Geschlechts in der Natur_, p. 19.]

[Footnote 15: Food affords the basis for metabolic changes in the
parent organism, but it is probable that food is less _directly_
related than heat and light to the determination of sex. Sachs, whose
experiments must be given the greatest possible weight, has determined
that the ultra-violet rays of light are necessary to the chemical
changes essential to the formation of the reproductive organs.
(J. Sachs, "Ueber die Wirkung der ultravioletten Strahlen auf die
Bluethenbildung," _Gesammelte Abhandlungen ueber Pflanzen-Physiologie_,
Vol. I, pp. 293ff.) More recently, Klebs has shown that by diminishing
the intensity of light the development of female sex or