

Contents 



Preface v 



Chapter One. Introduction l 



The Period of Descriptive Embryology 4 



The Period of Comparative Embryology 6 



The Period of Cellular Embryology 7 



The Period of Experimental Embryology 7 



The Embryologist as a Scientist 9 



Why the Embryology of the Frog? 10 



Some General Concepts in Embryology 11 



Biogenesis, 11; Biogenetic Law — The Law of Recapitulation, 11; Epi- 

 genesis vs. Preformationism, 12; Soma and Germ Plasm, 13; The Germ 

 Layer Concept, 14 



The Normal Sequence of Events in Embryology 14 



Chapter Two. General Introduction to the Embryology of the 



Leopard Frog, Rana pipiens 17 



Chapter Three. Reproductive System of the Adult Frog: Rana 



pipiens 31 



The Male 31 



Secondary Sexual Characters 31 



Primary Sexual Characters 31 



Reproductive Behavior 40 



Accessory Structures 41 



The Female 43 



Secondary Sexual Characters 43 



Primary Sexual Characters 43 



Chapter Four. Fertilization of the Frog's Egg 73 



Completion of Maturation of the Egg 77 



Penetration and Copulation Paths of the Spermatozoon 78 



Symmetry of the Egg, Zygote, and Future Embryo 82 



Chapter Five. Cleavage 87 



Chapter Six. Blastulation 93 



Chapter Seven. Gastrulation 97 



Significance of the Germ Layers 97 



Origin of Fate Maps 98 



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