CONTENTS. 



PAGE 



CHAPTER I. GENERAL CONCEPTIONS, 17-43 



The Vertebrate Type of Structure, 18 



The Principal Modifications of the Vertebrate Type, 22 



Definition of Anlage, 25 



A Summary of Embryological Development, 25 



Cytomorphosis, 27 



Comparison of Larval and Embryonic Types of Development, 32 



Germ-layers, 34 



The Relations of Surface to Mass, , 37 



The Law of Unequal Growth, 38 



Germ-cells, 39 



The Theory of Heredity, 40 



The Law of Recapitulation, 41 



CHAPTER II. THE EARLY DEVELOPMENT OF MAMMALS, 44-111 



The Spermatozoon, ... 44 



The Fully Grown Ovum before Maturation, . 45 



Ovulation, 46 



The Maturation of the Ovum, 47 



Impregnation of the Ovum, 49 



Segmentation of the Ovum, 54 



The Blastodermic Vesicle, 60 



The Embrvonic Shield, 62 



Origin of the Mesoderm, 63 



The Primitive Axis, 65 



The Notochordal Canal, 66 



The Notochord, 67 



The Ultimate Fate of the Notochord, 68 



The Origin of the Nervous System, 69 



The Structure of the Medullary Canal, , 7 1 



The Early History of the Mesoderm, 74 



Somatopleure and Splanchnopleure, "j6 



The Embryonic Coelom, 79 



The Mesenchyma, 83 



The Germ-cells, 84 



The Yolk-sac, 85 



The Origin of the Blood-vessels and Blood, 90 



The Blood-corpuscles, 93 



The Origin of the Heart, 96 



The Germinal Area, 97 



The Main Vessels of the Area Vasculosa, 97 



The Liver, loo 



The Oral and Anal Plates, IOO 



The Excretory Organs, IOI 



The Allantois, 103 



The Trophoblast, 106 



The Growth of the Embryo, 107 



The Umbilical Cord, : 109 



CHAPTER III. THE HUMAN EMBRYO, , 112-156 



Calculation of the Age of the Human Embryo, 112 



The Classification of the Early Stages, 113 



ix 



