[32] In this connexion it ought to be observed that Darwin believed the causes of variation to be internal as well as external—or arising from “the nature of the organism” no less—or even more—than from “changed conditions of life.” But although he appears to have entertained the admixture of hereditary endowments in sexual unions as one of the causes of variation belonging to the former category, he expressly says that he did not regard it as the only, or even the main, cause. (See _Variation_, &c., vol. i, pp. 197, 398; vol. ii, pp. 237, 252.) [33] See above, p. 54, note. [34] See _Darwin and after Darwin_, Part I, p. 129. [35] It must always be remembered that the view adopted by Weismann touching the nucleus (and more especially the chromosomes) of a germ-cell being the sole seat of heredity, is still far from having been established. [36] _Essays_, vol. ii. p. 122. [37] _The Germ-plasm_, p. 342. [38] _The Germ-plasm_, p. 342. [39] See, however, p. 83, note. [40] _Essays_, vol. i. p. 101. Italics mine. [41] _The Germ-plasm_, p. 406. [42] Galton, _loc. cit._, pp. 343-344. [43] Professor Weismann still maintains that there is a further important distinction between the theories of pangenesis and germ-plasm, in that the one is pre-formative while the other is epigenetic. But I am still unable to perceive that such is the case. He argues, indeed, that his new doctrine of determinants emphasizes this distinction: the argument, however, appears to me radically unsound. For instance, he says, “The hereditary continuation in each part is pre-determined in each part from the germ onwards. The right and left ears could not possibly resemble each other, if the relative strength of the hereditary tendencies on both sides were not pre-determined for all parts of the child by the nature of the paternal and maternal idants.” Very well. But, if so, the theory of determinants is just as much pre-formative as is that of gemmules. Or, conversely, the latter is quite as epigenetic as the former. Both are alike _determinative_, while neither supposes that the determination is due to a pre-formed miniature of the future child in the fertilized egg of its mother; but to a particulate _representation_ in the latter of every heritable part of the former. [44] By “germ” Galton means a carrier of heredity, which is capable of self-multiplication. In these fundamental respects, therefore, it is equivalent to a “gemmule” on the one hand and a “determinant” on the other. The three terms are so far synonymous. [45] _Loc. cit._, p. 338. [46] _Loc. cit._, p. 339. [47] _The Germ-plasm_, pp. 199, 220. [48] pp. 72-4. [49] _The Germ-plasm_, pp. 383-386. [50] Quoted from above, p. 78. [51] _Morph. Journal_, vol. ii. [52] See Appendix II. [53] _Essays on Heredity_, vol. ii. pp. 193-4. [54] See above, pp. 63-67. [55] _Nature_, vol. xli. p. 322. [56] _The Germ-plasm_, pp. 414-415. Italics Weismann’s. [57] _Essays_, vol. i. p. 284.