universe compels us to formulate a single supreme law--the all-embracing "Law of Substance," or the united laws of the constancy of matter and the conservation of energy. We should never have reached this supreme general conception if Charles Darwin--a "monistic philosopher" in the true sense of the word--had not prepared the way by his theory of descent by natural selection, and crowned the great work of his life by the association of this theory with a naturalistic anthropology. FOOTNOTES: [Footnote 127: _Generelle Morphologie der Organismen_, 2 vols., Berlin, 1866.] [Footnote 128: Eng. transl.; _The History of Creation_, London, 1876.] [Footnote 129: London, 1908.] [Footnote 130: Munich, 1884.] [Footnote 131: _Die Mutationstheorie_, Leipzig, 1903.] [Footnote 132: _Der Kampf der Theile im Organismus_, Leipzig, 1881.] [Footnote 133: Leipzig, 1904.] [Footnote 134: Berlin, 1876.] [Footnote 135: _Wonders of Life_, London and New York, 1904.] [Footnote 136: Eng. transl.; _The Evolution of Man_, 2 vols., London, 1879 and 1905.] [Footnote 137: _Origin of Species_ (6th edit.), p. 396.] [Footnote 138: Eng. transl.; _Facts and Arguments for Darwin_, London, 1869.] [Footnote 139: 3 vols., Berlin, 1894-96.] [Footnote 140: _Descent of Man_ (Popular Edit.), p. 927.] [Footnote 141: _Gesammelte Abhandlungen zur wissenschaftlichen Medizin_, Berlin, 1856.] [Footnote 142: Eng. transl.; _Last Words on Evolution_, London, 1906.] [Footnote 143: _Descent of Man_, (Popular Edit.), p. 255.] [Footnote 144: _Descent of Man_, p. 930.] [Footnote 145: Eng. transl.; _The History of Creation_, London, 1876.] [Footnote 146: Berlin, 1894-96.] [Footnote 147: Leipzig, 1874, 5th edit. 1905. Eng. transl.; _The Evolution of Man_, London, 1905.] [Footnote 148: London, 1898.] [Footnote 149: _Festschrift zur 350-jährigen Jubelfeier der Thüringer Universität Jena_. Jena. 1908.] [Footnote 150: London, 1885; 1888.] [Footnote 151: _The Riddle of the Universe_, London and New York, 1900.] [Footnote 152: _The Wonders of Life_, London and New York, 1904.] VI MENTAL FACTORS IN EVOLUTION BY C. LLOYD MORGAN, LLD., F.R.S