[Footnote 2: _Unity of Nature_. I consider the fundamental unity of inorganic and organic nature, as well as their genetic relation, to be an essential axiom of monism. I particularly emphasise this "article of faith" here, as there are still scientists of repute who contest it. Not only is the old mystical "vital power" brought back upon the stage again from time to time, but even the "miraculous" origin of organic life out of "dead" inorganic nature is often brought up still against the doctrines of evolution, as an insoluble riddle--as one of Du Bois-Reymond's "seven riddles of the world" (see his _Discourse on Leibnitz_, 1880). The solution of this "transcendent" riddle of the world, and of the allied question of archigony (equivocal generation, in a strictly defined meaning of the term), can only be reached by a critical analysis and unprejudiced comparison of matter, form, and energy in inorganic and organic nature. This I have already done (1866) in the second book of my _General Morphology_ (vol. i. pp. 109-238): "General Researches as to the Nature and First Beginning of Organisms, their Relation to things Inorganic, and their Division into Plants and Animals."] A short résumé of this is contained in Lecture XV. of my _Natural History of Creation_ (8th ed., pp. 340-370). The most serious difficulties which formerly beset the monistic view there given may now be held to have been taken out of the way by recent discoveries concerning the nature of protoplasm, the discovery of the Monera, the more accurate study of the closely-related single-celled Protista, their comparison with the ancestral cell (or fertilised egg-cell), and also by the chemical carbon-theory. (See my "Studies on Monera and other Protista," in the _Jenaische Zeitschrift für Naturwissenschaft_, vols. iv. and v., 1868-1870; also Carl Naegeli, _Mechanisch-physiologische Begründung der Abstammungslehre_, 1884.)]