Transcriber's note: Text enclosed by underscores is in italics (_italics_). A single underscore NH_3 introduces a subscript, and a caret 30^a a superscript. * * * * * THE PRINCIPLES OF BIOLOGY BY HERBERT SPENCER [Illustration] IN TWO VOLUMES VOLUME I NEW YORK AND LONDON D. APPLETON AND COMPANY 1910 COPYRIGHT, 1866, 1898, BY D. APPLETON AND COMPANY. PREFACE TO THE REVISED AND ENLARGED EDITION. Rapid in all directions, scientific progress has during the last generation been more rapid in the direction of Biology than in any other; and had this work been one dealing with Biology at large, the hope of bringing it up to date could not have been rationally entertained. But it is a work on the _Principles_ of Biology; and to bring an exposition of these up to date, seemed not impossible with such small remnant of energy as is left me. Slowly, and often interrupted by ill-health, I have in the course of the last two years, completed this first volume of the final edition. Numerous additions have proved needful. What was originally said about vital changes of matter has been supplemented by a chapter on "Metabolism." Under the title "The Dynamic Element in Life," I have added a chapter which renders less inadequate the conception of Life previously expressed. A gap in preceding editions, which should have been occupied by some pages on "Structure," is now filled up. Those astonishing actions in cell-nuclei which the microscope has of late revealed, will be found briefly set forth under the head of "Cell-Life and Cell-Multiplication." Further evidence and further thought have resulted in a supplementary chapter on "Genesis, Heredity, and Variation"; in which certain views enunciated in the first edition are qualified and developed. Various modern ideas are considered under the title "Recent Criticisms and Hypotheses." And the chapter on "The Arguments from Embryology" has been mainly rewritten. Smaller increments have taken the shape of new sections incorporated in pre-existing chapters. They are distinguished by the following section-marks:--§ 8a, § 46a, § 87a, § 100a, § 113a, § 127a, §§ 130a-130d. There should also be mentioned a number of foot-notes of some significance not present in preceding editions. Of the three additional appendices the two longer ones have already seen the light in other shapes.