[39]. Or more precisely, they must give up as many molecules as would correspond to the number of the kind of cell in question found in the mature organism.
[40]. See Darwin, ‘The Variation of Animals and Plants under Domestication,’ 1875, vol. ii. chapter xxvii. pp. 349-399.
[41]. 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.
[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.
[43]. ‘Physiologie der Zeugung.’
[44]. See ‘Ueber die Uebung,’ Berlin, 1881.
[45]. This principle was, I believe, first pointed out by Seidlitz. Compare Seidlitz, ‘Die Darwin’sche Theorie,’ Leipzig, 1875, p. 198.
[46]. W. Roux, ‘Der Kampf der Theile im Organismus,’ Leipzig, 1881.
[47]. Compare Born in ‘Zoolog. Anzeiger,’ 1883, No. 150, p. 537.
[48]. O. C. Marsh, ‘Odontornithes, a Monograph on the extinct toothed Birds of North America,’ Washington, 1880.