In the course of this book I have not hidden my own sympathy with the functional attitude. It appears to me probable that more insight will be gained into the real nature of life and organisation by concentrating on the active response of the animal, as manifested both in behaviour and in morphogenesis, particularly in the post-embryonic stages, than by giving attention exclusively to the historical aspect of structure, as is the custom of "pure morphology." I believe we shall only make progress in this direction if we frankly adopt the simple everyday conception of living things--which many of us have had drilled out of us--that they are active, purposeful agents, not mere complicated aggregations of protein and other substances. Such an attitude is probably quite as sound philosophically as the opposing one, but I have not in this place attempted any justification of it. I have touched very lightly upon the controversy between vitalism and materialism which has been revived with the early years of the present century. It hardly lends itself as yet to historical treatment, and I could hardly hope to maintain with regard to it that objective attitude which should characterise the historian. The main result I hope to have achieved with this book is the demonstration, tentative and incomplete as it is, of the essential continuity of animal morphology from the days of Aristotle down to our own time. It is unfortunately true that modern biology, perhaps in consequence of the great advances it has made in certain directions, has to a considerable extent lost its historical consciousness, and if this book helps in any degree to counteract this tendency so far as animal morphology is concerned, it will have served its purpose. I owe a debt of gratitude to my friends Dr James F. Gemmill and Prof. J. Arthur Thomson for much kindly encouragement and helpful criticism. The credit for the illustrations is due to my wife, Mrs Jehanne A. Russell. One is from Nature; the others are drawn from the original figures. E.S.R. CHELSEA, 1916. CONTENTS CHAP. PAGE I. THE BEGINNINGS OF COMPARATIVE ANATOMY 1 II. COMPARATIVE ANATOMY BEFORE CUVIER 17 III. CUVIER 31 IV. GOETHE 45 V. ETIENNE GEOFFROY ST HILAIRE 52 VI. THE FOLLOWERS OF ETIENNE GEOFFROY ST HILAIRE 79 VII. THE GERMAN TRANSCENDENTALISTS 89 VIII. TRANSCENDENTAL ANATOMY IN ENGLAND--RICHARD OWEN 102 IX. KARL ERNST VON BAER 113 X. THE EMBRYOLOGICAL CRITERION 133 XI. THE CELL-THEORY 169 XII. THE CLOSE OF THE PRE-EVOLUTIONARY PERIOD 190 XIII. THE RELATION OF LAMARCK AND DARWIN TO MORPHOLOGY 213