CONTENTS. 



CHAPTER I. GENERAL CONCEPTIONS, i 



The Segmented Animals. Metamerism, 2 



The Vertebrate Type of Structure, 2 



The Principal Modifications of the Vertebrate Type, 7 



Definition of Anlage, 9 



A Summary of Embryological Development, 10 



Cytomorphosis, 1 1 



Comparison of Larval and Embryonic Types of Development, 16 



Germ-layers, * 18 



The Relations of Surface to Mass, 20 



Classification of Glands, 23 



The Law of Unequal Growth, 24 



Germ-cells, 25 



Sex, 27 



The Theory of Heredity, 28 



The Law of Recapitulation, 29 



Arrest of Development, 31 



CHAPTER II. THE EARLY DEVELOPMENT OF MAMMALS, 33 



The Spermatozoon, 33 



The Fully Grown Ovum Before Maturation, 34 



Ovulation, 35 



The Maturation of the Ovum, . . . 36 



Impregnation of the Ovum, 38 



Segmentation of the Ovum, 4 2 



The Blastodermic Vesicle, 45 



The Embryonic Shield, 47 



Growth of the Embryo and Separation of the Yolk, 49 



Origin of the Mesoderm, 51 



The Primitive Axis, ' 5 2 



The Notochordal Canal, ; 53 



The Notochord, * 55 



The Ultimate Fate of the Notochord, 56 



The Archenteron, 57 



The Oral and Anal Plates, 58 



The Digestive Canal, 59 



The Yolk-sac, 63 



The Origin of the Nervous System, 67 



The Structure of the Medullary Canal, ' 69 



Origin of Nerves, 7 2 



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