A translation of Essays I and II was commenced by Mr. A. E. Shipley during his residence at Freiburg in the winter of 1884. His work was greatly aided by the kind assistance of Dr. van Rees of Amsterdam, to whom we desire to express our most sincere thanks. The translation was laid aside until the summer of 1888, when Mr. Shipley was invited to co-operate with the other editors in the preparation of the present volume; the Clarendon Press having consented to publish the complete series of essays as one of their Foreign Biological Memoirs. We think it probable that this work may interest many who are not trained biologists, but who approach the subject from its philosophical or social aspects. Such readers would do well to first study Essays I, II, VII, and VIII, inasmuch as some preparation for the more technical treatment pursued in the other essays will thus be gained. The notes signed A. W. and dated, were added by the author during the progress of the translation. The notes included in square brackets were added by the Editors; the authorship being indicated by initials in all cases. In conclusion, it is our pleasant duty to thank those who have kindly helped us by reading the proof-sheets and making valuable suggestions. Our warmest thanks are due to Mrs. Arthur Lyttelton, Mr. W. Hatchett Jackson, Deputy Linacre Professor in the University of Oxford, Mr. J. S. Haldane, and Professor R. Meldola. Important suggestions were also made by Professor E. Ray Lankester, Mr. Francis Galton, and Dr. A. R. Wallace. Professor W. N. Parker also greatly helped us by looking over the proof-sheets with Professor Weismann. E. B. P. S. S. A. E. S. Oxford, _February, 1889_. ------------------------------------------------------------------------ CONTENTS. _Translator._ A. E. Shipley I. The Duration of Life, 1881 1 II. On Heredity, 1883 67 III. Life and Death, 1883 107 _Translator._ Selmar Schönland IV. The Continuity of the Germ-plasm as the 161 Foundation of a Theory of Heredity, 1885 V. The Significance of Sexual Reproduction 251 in the Theory of Natural Selection, 1886 VI. On the Number of Polar Bodies and their 333 Significance in Heredity, 1887 VII. On the Supposed Botanical Proofs of the 385 Transmission of Acquired Characters, 1888. VIII. The Supposed Transmission of 419 Mutilations, 1888 ------------------------------------------------------------------------