In this sense I trust that the sign-post or compass which I offer may be accepted. Even though it should be its fate to be replaced by a better one at a later period, it will have fulfilled its object if it enables science to advance for even a short distance. ------------------------------------------------------------------------ Footnotes for Essay V. Footnote 176: C. Nägeli, ‘Mechanisch-physiologische Theorie der Abstammungslehre.’ München u. Leipzig, 1884. Footnote 177: ‘Ueber die Berechtigung der Darwin’schen Theorie.’ Leipzig, 1868, p. 27. Footnote 178: l. c., Preface, p. vi. Footnote 179: Since the above was written many other morphological peculiarities of plants have been rightly explained as adaptations. Compare, for instance, the investigations of Stahl on the means by which plants protect themselves against the attacks of snails and slugs (Jena, 1888).—A. W., 1888. Footnote 180: l. c., pp. 117, 286. Footnote 181: Compare the second and fourth of the preceding Essays, ‘On Heredity’ and ‘The Continuity of the Germ-plasm as the Foundation of a Theory of Heredity.’ Footnote 182: Compare Rauber, ‘Homo sapiens ferus oder die Zustände der Verwilderten.’ Leipzig, 1885. Footnote 183: ‘Sitzungsberichte der baierischen Akademie der Wissenschaften,’ vom 18 Nov. 1865. Compare also his ‘Mechanisch-physiologische Theorie der Abstammungslehre,’ p. 102, etc. Footnote 184: Jordan, ‘Remarques sur le fait de l’existence en société des espèces végétales affines.’ Lyon, 1873. Footnote 185: S. Hermann’s ‘Handbuch der Physiologie,’ Theil II; ‘Physiologie der Zeugung,’ by V. Hensen. Footnote 186: E. van Beneden, ‘Recherches sur la maturation de l’œuf, la fécondation et la division cellulaire.’ Gand u. Leipzig, 1883, pp. 404 et seq. Footnote 187: Rolph, ‘Biologische Probleme.’ Leipzig, 1882. Footnote 188: Cienkowsky, ‘Arch. f. mikr. Anat.,’ ix. p. 47. 1873. Footnote 189: Hensen, ‘Physiologie der Zeugung,’ p. 139. Footnote 190: Coalescence takes place in the so-called bud-like conjugation of _Vorticellidae_ and _Trichodinidae_, etc. Footnote 191: Compare (1) Bardeleben, ‘Zur Entwicklung der Fusswurzel,’ Sitzungsber. d. Jen. Gesellschaft, Jahrg. 1885, Feb. 6; also ‘Verhandl. d. Naturforscherversammlung zu Strassburg,’ 1885, p. 203; (2) G. Baur, ‘Zur Morphologie des Carpus und Tarsus der Wirbelthiere,’ Zool. Anzeiger, 1885, pp. 326, 486. Footnote 192: In frogs the sixth toe exists in the hind legs as a rudimentary prehallux. Compare Born, Morpholog. Jahrbuch, Bd. I, 1876. Footnote 193: I here make use of the same illustration which I employed in my first attempt to explain the effects of _panmixia_. Compare the second Essay ‘On Heredity.’ Footnote 194: