XIV. ERNST HAECKEL AND CARL GEGENBAUR 246 XV. EARLY THEORIES ON THE ORIGIN OF VERTEBRATES 268 XVI. THE GERM-LAYERS AND EVOLUTION 288 XVII. THE ORGANISM AS AN HISTORICAL BEING 302 XVIII. THE BEGINNINGS OF CAUSAL MORPHOLOGY 314 XIX. SAMUEL BUTLER AND THE MEMORY THEORIES OF HEREDITY 335 XX. THE CLASSICAL TRADITION IN MODERN MORPHOLOGY 345 INDEX 365 ILLUSTRATIONS FIG. PAGE 1. HYOID ARCH OF THE CONGER. (ORIGINAL.) 58 2. "VERTEBRA" OF A PLEURONECTID. (GEOFFROY.) 61 3. ABDOMINAL SEGMENT OF THE LOBSTER. (GEOFFROY.) 63 4. IDEAL TYPICAL VERTEBRA. (OWEN.) 102 5. NATURAL TYPICAL VERTEBRA. (OWEN.) 103 6. THE ARCHETYPE OF THE VERTEBRATE SKELETON. (OWEN.) 105 7. IDEAL TRANSVERSE SECTION OF A VERTEBRATE EMBRYO. (VON BAER.) 119 8. GILL-SLITS OF THE PIG EMBRYO. (RATHKE.) 134 9. MECKEL'S CARTILAGE AND EAR-OSSICLES IN EMBRYO OF PIG. (REICHERT.) 145 10. CRANIAL VERTEBRAE AND VISCERAL ARCHES IN EMBRYO OF PIG. (REICHERT.) 148 11. EMBRYONIC CRANIUM OF THE ADDER. (RATHKE.) 152 12. TRANSVERSE SECTION OF CHICK EMBRYO. (REMAK.) 211 13. DEVELOPMENT OF THE ASCIDIAN LARVA (KOWALEVSKY.) 272 14. TRANSVERSE SECTION OF THE WORM _NAIS_. (SEMPER.) 280 15. THE FIVE PRIMARY STAGES OF ONTOGENY. (HAECKEL.) 292 FORM AND FUNCTION CHAPTER I THE BEGINNINGS OF COMPARATIVE ANATOMY The first name of which the history of anatomy keeps record is that of Alcmaeon, a contemporary of Pythagoras (6th century B.C.). His interests appear to have been rather physiological than anatomical. He traced the chief nerves of sense to the brain, which he considered to be the seat of the soul, and he made some good guesses at the mechanism of the organs of special sense. He showed that, contrary to the received opinion, the seminal fluid did not originate in the spinal cord. Two comparisons are recorded of his, one that puberty is the equivalent of the flowering time in plants, the other that milk is the equivalent of white of egg.[1] Both show his bias towards looking at the functional side of living things. The latter comparison reappears in Aristotle. A century later Diogenes of Apollonia gave a description of the venous system. He too placed the seat of sensation in the brain. He assumed a vital air in all living things, being in this influenced by Anaximenes whose primitive matter was infinite air. In following out this thought he tried to prove that both fishes and oysters have the power of breathing.[2]