akly and
without energy. The addition of an extract of sheep's brains made
them perfectly fresh and vigorous again. Further experiments in this
direction are to be desired, but, according to those of Calkins, it is
probable that Infusorians can continue to live for an unlimited time
even without conjugation. (Ibid., note.)]

[Footnote 19: Westermarck, _loc. cit._, pp. 476-83, following a
suggestion of Duesing, has brought together much of the evidence on
this point, but the application of the facts here made has not, I
believe, been suggested.]

[Footnote 20: A. von Oettingen, _Die Moralstatistik_, 3. Aufl., p.
56.]

[Footnote 21: Duesing, _Die Regulirung des Geschlechtsverhaeltnisses_,
p. 237.]

[Footnote 22: Westermarck, _loc. cit._, pp. 479 and 481 n.]

[Footnote 23: Cf. _ibid._, pp. 476-83.]

[Footnote 24: G. Delaunay, "De l'egalite et inegalite des deux sexes,"
_Revue scientifique_, September 3, 1881; C. Darwin, _Descent of Man_,
chap. 10.]

[Footnote 25: A. Weismann, _Essays on Heredity_, Vol. I, "The Duration
of Life," has shown that size and longevity are determined by natural
selection.]

[Footnote 26: Darwin, _Descent of Man_, chap. 8.]

[Footnote 27: Ibid.]

[Footnote 28: A.R. Wallace, _Contributions to the Theory of Natural
Selection_, chap. 3.]

[Footnote 29: "If we take the highly decorated species--that is,
animals marked by alternate dark or light bands or spots, such as the
zebra, some deer, or the carnivora--we find, first, that the region
of the spinal column is marked by a dark stripe; secondly, that the
regions of the appendages, or limbs, are differently marked; thirdly,
that the flanks are striped or spotted along or between the regions of
the lines of the ribs; fourthly, that the shoulder and hip regions
are marked by curved lines; fifthly, that the pattern changes, and the
direction of the lines or spots, at the head, neck, and every joint of
the limbs; and, lastly, that the tips of the ears, nose, tail, and
the feet and the eye are emphasized in color. In spotted animals
the greatest length of the spot is generally in the direction of
the largest development of the skeleton."--A. Tylor, _Coloration in
Animals and Plants_, p. 92.]

[Footnote 30: A.R. Wallace, _Darwinism_, chap. 10.]

[Footnote 31: Professor Carl Pearson, in a severe, not to say
unmannerly, paper ("Variation in Man and Woman," _The Chances of
Death_, Vol. I), has criticized some of the results of the physical