To this class of phenomena of course belong those acts of will which call forth the functional activity of certain groups of cells. It is quite clear that such impulses do not originate in the constitution of the tissue in question, but are due to the operation of external causes. The activity does not arise directly from any natural disposition of the germ, but is the result of accidental external impressions. A domesticated duck uses its legs in a different manner from, and more frequently than a wild duck, but such functional changes are the consequence of changed external conditions, and are not due to the constitution of the germ. Footnote 42: Upon this subject Pflüger states—‘I have made myself accurately acquainted with all facts which are supposed to prove the inheritance of acquired characters,—that is of characters which are not due to the peculiar organization of the ovum and spermatozoon from which the individual is formed, but which follow from the incidence of accidental external influences upon the organism at any time in its life. Not one of these facts can be accepted as a proof of the transmission of acquired characters.’ _l. c._ p. 68. Footnote 43: ‘Physiologie der Zeugung.’ Footnote 44: See ‘Ueber die Uebung,’ Berlin, 1881. Footnote 45: This principle was, I believe, first pointed out by Seidlitz. Compare Seidlitz, ‘Die Darwin’sche Theorie,’ Leipzig, 1875, p. 198. Footnote 46: W. Roux, ‘Der Kampf der Theile im Organismus,’ Leipzig, 1881. Footnote 47: Compare Born in ‘Zoolog. Anzeiger,’ 1883, No. 150, p. 537. Footnote 48: O. C. Marsh, ‘Odontornithes, a Monograph on the extinct toothed Birds of North America,’ Washington, 1880. Footnote 49: C. Darwin, ‘Variation of Animals and Plants under Domestication.’ Vol. I. Footnote 50: Compare ‘Der thierische Wille,’ Leipzig, 1880. Footnote 51: Steller’s interesting account of the Sea-cow (_Rhytina Stelleri_) proves that this suggestion is valid. This large mammal was living in great numbers in Behring Strait at the end of the last century, but has since been entirely exterminated by man. Steller, who was compelled by shipwreck to remain in the locality for a whole year, tells us that the animals were at first without any fear of man, so that they could be approached in boats and could thus be killed. After a few months however the survivors became wary, and did not allow Steller’s men to approach them, so that they were difficult to catch.—A. W., 1888. Footnote 52: Compare Schneider, ‘Der thierische Wille.’ Footnote 53: [The author refers to the Academy of Arts at Munich. S. S.] Footnote 54: Compare Darwin’s ‘Descent of Man.’ Footnote 55: ‘Studien zur Descendenztheorie, I. Ueber den Saison-Dimorphismus der Schmetterlinge.’ Leipzig, 1875. English edition translated and edited by Professor Meldola, ‘Studies in the Theory of Descent,’ Part I. Footnote 56: