Such parts of the Preface as more particularly refer to Isolation and Physiological Selection are reserved for publication in Part III. A year or more must elapse before that part will be ready for publication. Mr. F. Howard Collins has, as a kindly tribute to the memory of the author, read through the proofs. Messrs. F. Darwin, F. Galton, H. Seebohm, and others, have rendered incidental assistance. After much search I am unable to give the references to one or two passages. I have allowed a too flattering reference to myself to stand, in accordance with a particular injunction of Mr. Romanes given shortly before that sad day on which he died, leaving many to mourn the loss of a personal friend most bright, lovable, and generous-hearted, and thousands to regret that the hand which had written so much for them would write for them no more. C. LL. M. UNIVERSITY COLLEGE, BRISTOL, _April, 1894_. CONTENTS PAGE CHAPTER I. INTRODUCTORY: THE DARWINISM OF DARWIN AND OF THE POST-DARWINIAN SCHOOLS 1 CHAPTER II. CHARACTERS AS HEREDITARY AND ACQUIRED (_Preliminary_) 39 CHAPTER III. CHARACTERS AS HEREDITARY AND ACQUIRED (_Continued_) A. _Indirect evidence in favour of the Inheritance of Acquired Characters_ 60 B. _Inherited effects of Use and of Disuse_ 95 CHAPTER IV. CHARACTERS AS HEREDITARY AND ACQUIRED (_Continued_) C. _Experimental evidence in favour of the Inheritance of Acquired Characters_ 103 CHAPTER V. CHARACTERS AS HEREDITARY AND ACQUIRED (_Continued_) A. and B. _Direct and Indirect Evidence in favour of the Non-inheritance of Acquired Characters_ 133 C. _Experimental Evidence as to the Non-inheritance of Acquired Characters_ 142 CHAPTER VI. CHARACTERS AS HEREDITARY AND ACQUIRED (_Conclusion_) 150 CHAPTER VII. CHARACTERS AS ADAPTIVE AND SPECIFIC 159 CHAPTER VIII. CHARACTERS AS ADAPTIVE AND SPECIFIC (_Continued_) I. _Climate_ 200 II. _Food_ 217 III. _Sexual Selection_ 219 IV. _Isolation_ 223 V. _Laws of Growth_ 226 CHAPTER IX. CHARACTERS AS ADAPTIVE AND SPECIFIC (_Continued_) 228 CHAPTER X. CHARACTERS AS ADAPTIVE AND SPECIFIC (_Concluded_) 251 SUMMARY 274 APPENDIX I. ON PANMIXIA 291