Along with larger motives, one motive which has joined in prompting the foregoing articles, has been the desire to point out that already among biologists, the beliefs concerning the origin of species have assumed too much the character of a creed; and that while becoming settled they have been narrowed. So far from further broadening that broader view which Mr. Darwin reached as he grew older, his followers appear to have retrograded towards a more restricted view than he ever expressed. Thus there seems occasion for recognizing the warning uttered by Prof. Huxley, as not uncalled for. Whatever may be thought of the arguments and conclusions set forth in this article and the preceding one, they will perhaps serve to show that it is as yet far too soon to close the inquiry concerning the causes of organic evolution. ----- Footnote 2: Though Mr. Darwin approved of this expression and occasionally employed it, he did not adopt it for general use; contending, very truly, that the expression Natural Selection is in some cases more convenient. See _Animals and Plants under Domestication_ (first edition) Vol. i, p. 6; and _Origin of Species_ (sixth edition) p. 49. Footnote 3: It is true that while not deliberately admitted by Mr. Darwin, these effects are not denied by him. In his _Animals and Plants under Domestication_ (vol. ii, 281), he refers to certain chapters in the _Principles of Biology_, in which I have discussed this general inter-action of the medium and the organism, and ascribed certain most general traits to it. But though, by his expressions, he implies a sympathetic attention to the argument, he does not in such way adopt the conclusion as to assign to this factor any share in the genesis of organic structures—much less that large share which I believe it has had. I did not myself at that time, nor indeed until quite recently, see how extensive and profound have been the influences on organization which, as we shall presently see, are traceable to the early results of this fundamental relation between organism and medium. I may add that it is in an essay on “Transcendental Physiology,” first published in 1857, that the line of thought here followed out in its wider bearings, was first entered upon. Footnote 4: _Text-Book of Botany_, &c. by Julius Sachs. Translated by A. W. Bennett and W. T. T. Dyer. Footnote 5: _A Manual of the Infusoria_, by W. Saville Kent. Vol. i, p. 232. Footnote 6: _Ib._ Vol. i, p. 241. Footnote 7: Kent, Vol. i, p. 56. Footnote 8: _Ib._ Vol. i, p. 57. Footnote 9: _The Elements of Comparative Anatomy_, by T. H. Huxley, pp. 7-9. Footnote 10: _A Treatise on Comparative Embryology_, by F. M. Balfour, Vol. ii, chap. xiii. Footnote 11: Sachs, p. 210. Footnote 12: _Ibid._ pp. 83-4. Footnote 13: _Ibid._ p. 185. Footnote 14: _Ibid._ p. 80. Footnote 15: Sachs, p. 83. Footnote 16: _Ibid._ p. 147. Footnote 17: