Produced by Marilynda Fraser-Cunliffe, LN Yaddanapudi and the Online Distributed Proofreading Team at https://www.pgdp.net DARWIN, AND AFTER DARWIN III POST-DARWINIAN QUESTIONS ISOLATION AND PHYSIOLOGICAL SELECTION BY THE SAME AUTHOR. DARWIN, AND AFTER DARWIN. An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions. 1. THE DARWINIAN THEORY. With portrait of Darwin. 460 pages. 125 illustrations. Cloth, $2.00. 2. POST-DARWINIAN QUESTIONS. Edited by Prof. C. Lloyd Morgan. With portrait of G. J. Romanes. 338 pages. Cloth, $1.50. 3. POST-DARWINIAN QUESTIONS. ISOLATION AND PHYSIOLOGICAL SELECTION. Edited by Prof. C. Lloyd Morgan. With portrait of Mr. J. T. Gulick. 181 pages. Cloth, $1.00. All three volumes together, $4.00 net. AN EXAMINATION OF WEISMANNISM. With portrait of Weismann. 236 pages. Cloth, $1.00. THOUGHTS ON RELIGION. Edited by Charles Gore, M.A., Canon of Westminster. Third Edition. 184 pages. Cloth, gilt top, $1.25. THE OPEN COURT PUBLISHING COMPANY, 324 DEARBORN STREET, CHICAGO. [Illustration: Frontispiece--John J. Gulick] DARWIN, AND AFTER DARWIN _AN EXPOSITION OF THE DARWINIAN THEORY AND A DISCUSSION OF POST-DARWINIAN QUESTIONS_ BY THE LATE GEORGE JOHN ROMANES, M.A., LL.D., F.R.S. _Honorary Fellow of Gonville and Caius College, Cambridge_ III POST-DARWINIAN QUESTIONS ISOLATION AND PHYSIOLOGICAL SELECTION Chicago THE OPEN COURT PUBLISHING COMPANY 1906 CHAPTER 1. COPYRIGHTED BY THE OPEN COURT PUBLISHING CO. 1897. The Lakeside Press R. R. DONNELLEY & SONS CO., CHICAGO PREFACE Of the six chapters which constitute this concluding volume of G. J. Romanes' _Darwin, and after Darwin_, three, the first two and the last, were in type at the time of his death. I have not considered myself at liberty to make any alterations of moment in these chapters. For the selection and arrangement of all that is contained in the other three chapters I am wholly responsible. Two long controversial Appendices have been omitted. Those marked A and B remain in accordance with the author's expressed injunctions. In a third, marked C, a few passages from the author's note-books or MSS. have been printed. The portrait of the Rev. J. Gulick, which forms the frontispiece, was prepared for this volume before the author's death. Mr. Gulick's chief contributions to the theory of physiological selection are to be found in the Linnean Society's _Journal_ (_Zoology_, vols. xx and xxiii), and in four letters to _Nature_ (vol. xli. p. 536; vol. xlii. pp. 28 and 369; and vol. xliv. p. 29).