them by critics and others. Nevertheless, he has continued to make this practical protest.
Since completing his Philosophy, Mr. Spencer has occupied his working hours with the revision of the Principles of Biology, making the modifications and incorporating the new facts which the progress of the science demands. He recognizes that the advance has been more rapid in this branch than in any other; and that while it might be almost hopeless for him at his time of life to bring a work on biology at large up to date, the case is different in an exposition of the Principles of Biology. The additions to the work include a chapter on Metabolism supplementing the discussion of vital changes of matter; a chapter on the Dynamic Element in Life, to render less inadequate the conception of life previously expressed; some pages on Structure; an account, under the head of Cell Life and Cell Multiplication, of the astonishing actions in cell nuclei which the microscope has revealed; a further chapter on Genesis, Heredity, and Variation, in which certain views enunciated in the first edition of the book are qualified and developed; a review of various modern ideas under the title of Recent Criticisms and Hypotheses; a rewriting of most of the chapter on The Argument from Embryology; and a number of changes incorporated as sections in pre-existing chapters. The articles on Weissmannism are incorporated in an appendix. In performing this work assistance was needed, and the author sought and received criticism and help from different persons, each taking a division falling within the range of his special studies: Prof. W. H. Perkin in organic chemistry and its derived subjects; Prof. A. G. Tansley in plant morphology and physiology; Prof. E. W. MacBride and Mr. J. T. Cunningham in animal morphology; and Mr. W. B. Hardy in animal physiology. The first volume of this work, recently published, has been received with favor by persons of all shades of opinion respecting the questions it touches. The London Times, in not the friendliest of criticisms, says that even persons who do not accept the author's Philosophy will rejoice that he has been able to complete it, and adds that as it stands it "is a marvel of erudition: every page exhibits the wealth and variety of illustration for which Mr. Spencer is justly famous." The latest notice of it that we have observed, a French one in the Revue Scientifique, says that in consulting it biologists "will not lose their time, and many will find valuable ideas in it, suggestions by which their experimental work can not fail to be greatly benefited. And, like us, they will be filled with admiration for a work so condensed, and at the same time so admirably co-ordinated, so replete with facts and ideas, of the philosopher who has exercised so great an influence on the science of his times, and who is one of the finest intellectual
