[300] “Über die Berechtigung,” &c., Leipzig, 1868. In this work will be found briefly laid down the theoretical conception of variability here propounded somewhat more broadly. [In the last edition of the “Origin of Species” Darwin states, with respect to the direct action of the conditions of life as producing variability, that in every case there are two factors, “the nature of the organism and the nature of the conditions.” 6th ed. p. 6. R.M.] [301] [Although hardly necessary to the evolutionist, it may perhaps be well to remind the general reader, that all experiments upon spontaneous generation, or abiogenesis, have hitherto yielded negative results; no life is produced when the proper precautions are taken for excluding atmospheric germs. But although we have so far failed to reproduce in our laboratories the peculiar combination of conditions necessary to endow colloidal organic matter with the property of “vitality,” the consistent evolutionist is bound to believe, from the analogy of the whole of the processes of nature, that at some period of the earth’s history the necessary physical and chemical conditions obtained, and that some simple form or forms of life arose “spontaneously,” _i.e._ by the operation of natural causes. R.M.] [302] See Haeckel’s “Generelle Morphologie,” vol. ii. p. 203, and Seidlitz, “Die Darwin’sche Theorie,” 1875, p. 92 _et seq._ [303] [In a recently published work by Dr. Wilhelm Roux this author has attempted to work out the idea of an analogy between the struggle for existence and survival of the fittest in individuals and species, and the struggle for existence and survival of the parts in the individual organism. See “Der Kampf der Theile im Organismus: ein Beitrag zur Vervollständigung der mechanischen Zweckmässigkeitslehre,” Leipzig, 1881. R.M.] [304] [Eng. ed. Meanwhile it has been shown by Oscar Schmidt that Von Hartmann, under the name of “the Unconscious,” re-invests the old vital force with some portion of its former power. “Die naturwissenschaftlichen Grundlagen der Philosophie des Unbewussten,” Leipzig, 1877, p. 41.] [305] _Loc. cit._ p. 175. [306] _Loc. cit._ p. 156. [307] “Über die Cuninen-Knospenähren im Magen von Geryonien.” Reprint from “Mittheil. des naturwiss. Vereines,” Graz, 1875. [308] [See Darwin’s “Origin of Species,” 6th ed. pp. 33, 34, and 201-204. R.M.] [309] [Eng. ed. See Kant’s “Allgemeine Naturgeschichte und Theorie des Himmels.”] [310] “Das Unbewusste vom Standpunke der Physiologie und Descendenz-Theorie,” Berlin, 1872, p. 16. [311] [Eng. ed. See Lotze’s “Mikrokosmos,” 1st ed., vol. iii. pp. 477-483.] [312] See Helmholtz’s “Populäre wissenschaftl. Vorträge,” vol. ii., Brunswick, 1872. [313] See also Fr. Vischer’s “Studien über den Traum. Beilage zur Augsburger Allgem. Zeitung,” April 14th, 1876. Haeckel also includes this idea in his recent essay already quoted, “Die Perigenesis der Plastidule,” Berlin, 1876, p. 38 _et seq._