I have not been able to throw light upon all sides of the question which we are here discussing. There are still some essential points which I must leave for the present; and, furthermore, I am not yet in a position to explain satisfactorily all the details which arise at every step of the argument. But it appeared to me to be necessary to state this weighty and fundamental question, and to formulate it concisely and definitely; for only in this way will it be possible to arrive at a true and lasting solution of the problem. We must however be clear on this point—that the understanding of the phenomena of heredity is only possible on the fundamental supposition of the continuity of the germ-plasm. The value of experiment in relation to this question is somewhat doubtful. A careful collection and arrangement of facts is far more likely to decide whether, and to what extent, the continuity of germ-plasm is reconcilable with the assumption of the transmission of acquired characters from the parent body to the germ, and from the germ to the body of the offspring. At present such transmission is neither proved as a fact, nor has its assumption been shown to be unquestionably necessary. ------------------------------------------------------------------------ Footnotes for Essay II. Footnote 33: Pflüger, ‘Ueber den Einfluss der Schwerkraft auf die Theilung der Zellen und auf die Entwicklung des Embryo,’ Arch. f. Physiol. Bd. XXXII. p. 68, 1883. Footnote 34: Victor Hensen in his ‘Physiologie der Zeugung,’ Leipzig, 1881, p. 216. Footnote 35: That is for the preservation of its life. Footnote 36: Compare Weismann, ‘Die Entstehung der Sexualzellen bei den Hydromedusen,’ Jena, 1883. Footnote 37: It is doubtful whether _Magosphaera_ should be looked upon as a mature form; but nothing hinders us from believing that species have lived, and are still living, in which the ciliated sphere has held together until the encystment, that is the reproduction, of the constituent single cells. Footnote 38: Or is an exception perhaps afforded by the nutritive cells of the egg, which occur in many animals? Footnote 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. Footnote 40: See Darwin, ‘The Variation of Animals and Plants under Domestication,’ 1875, vol. ii. chapter xxvii. pp. 349-399. Footnote 41: