[Footnote 16:  E. Maupas, “Theorie de la sexualite des Infusoires cilies,” Comptes rendus, Vol.  CV, pp. 356ff.]

[Footnote 17:  The extinction took place at about the 330th generation in Onychodromus grandis, at about the 320th generation in Stylonichia mytilis, at about the 330th generation in Leucophrys patula, and at about the 660th generation in Oxytricha (indeterminate). (Maupas, loc. cit., p. 358.)]

[Footnote 18:  Maupas, loc. cit., p. 358.  Later investigations have tended to discredit Maupas’ experiments as a whole by showing that the Infusorians with which he experimented can be kept alive indefinitely by a change of diet, without the aid of sexual conjugation.  This merely confirms the view, however, that abundant nutrition and crossing are alike favorable to health:  “We must admire the skill of the investigator who was able to keep his colonies alive for months and years under such artificial conditions, but we may venture to doubt whether the fate of extinction which did ultimately overtake them was really due to the absence of conjugation, and not to the unnaturalness of the conditions.”  A. Weismann, The Evolution of Theory, Vol.  I, p. 329.

Since the above was written, Calkins has made a series of new experiments, the results of which differed in several respects from those yielded by Maupas’ experiments.  When his infusorian cultures began to grow weaker, as happened frequently and at irregular intervals, he was always able to restore them to more vigorous life by a change of diet, and especially by substituting grated meat, liver, and the like for infusions of hay.  Certain salts too, had the same effect; the animals became perfectly vigorous again.  Calkins believes that chemical agents, and especially salts, must be supplied to the protoplasm from time to time.  He reared 620 generations of Paramoecium without conjugation.  But the 620th was weakly 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.]