Form and Function | Page 2

PRE-EVOLUTIONARY PERIOD 190
XIII. THE RELATION OF LAMARCK AND DARWIN TO MORPHOLOGY 213
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 VERTEBR? 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]
A more strictly morphological note is struck by a curious saying of Empedocles (4th century B.C.), that "hair and foliage and the thick plumage of birds are one."[3]
In the collected writings of Hippocrates and his school, the Corpus Hippocraticum, of which no part is later than the end of the 5th century, there are recorded many anatomical facts. The author of the treatise "On the Muscles" knew, for instance, that the spinal marrow is different from ordinary marrow and has membranes continuous with those of the brain. Embryos of seven days (!) have all the parts of the body plainly visible. Work on comparative embryology is contained in the treatise "On the Development of the Child."[4]
The author of the treatise "On the Joints," which Littr�� calls "the great surgical monument of antiquity," is to be credited with the first systematic attempt at comparative anatomy, for he compared the human skeleton with that of other Vertebrates.
Aristotle (384-322 B.C.)[5] may fairly be said to be the founder of comparative anatomy, not because he was specially interested in problems of "pure morphology," but because he described the structure of many animals and classified them in a scientific way. We shall discuss here the morphological ideas which occur in his writings upon animals--in the Historia Animialium, the De Partibus Animalium, and the De Generatione Animalium.
The Historia Animalium is a most comprehensive work, in some ways the finest text-book of Zoology ever written. Certainly few modern text-books take such a broad and sane view of living creatures. Aristotle never forgets that form and structure are but one of the many properties of living things; he takes quite as much interest in their behaviour, their ecology, distribution, comparative physiology. He takes a special interest in the comparative physiology of reproduction. The Historia Animalium contains a description of the form and structure of man and of as many animals as Aristotle was acquainted with--and he was acquainted with an astonishingly large number. The later De Partibus Animalium is a treatise on the causes of the form and structure of animals. Owing to the importance which Aristotle ascribed to the final cause this work became really a treatise on the functions of the parts, a discussion of the problems of the relation of form to function, and the adaptedness of structure.
Aristotle was quite well aware that each of the big groups of animals was built upon one plan of structure, which showed endless variations "in excess and defect" in the different members of the group. But he did not realise that this fact