vill CONTENTS. 



CHAPTER V. 



CLEAVAGE (SEGMENTATION) 42 



Forms of Cleavage 42 



Holoblastic Cleavage 43 



Meroblastic Cleavage 45 



Some General Features of Cleavage Cleavage in Mammals 47 



Practical Suggestions 53 



References for Further Study 54 



CHAPTER VI. 



GERM LAYERS 55 



The Two Primary Germ Layers Formation of the Gastrula 55 



Gastrulation in Amphioxus 55 



Gastrulation in Amphibians 56 



Gastrulation in Reptiles and Birds 61 



Gastrulation in Mammals 67 



Formation of the Middle Germ Layer Mesoderm 72 



Mesoderm Formation in Amphioxus .- 72 



Mesoderm Formation in Amphibians 76 



Mesoderm Formation in Reptiles and Birds 78 



Mesoderm Formation in Mammals 85 



The Germ Layers in Man 89 



Practical Suggestions 96 



References for Further Study 97 



CHAPTER VII. 



FOETAL MEMBRANES 99 



Fcetal Membranes in Birds and Reptiles 99 



The Amnion 99 



The Yolk Sac 103 



The Allantois 106 



The Chorion or Serosa 107 



Fcetal Membranes in Mammals 107 



Amnion, Chorion, Yolk Sac, Allantois, Umbilical Cord 108 



Further Development of the Chorion m 



The Fcetal Membranes in Man 115 



The Amnion 115 



The Yolk Sac 117 



The Allantois 118 



The Chorion and Decidua 119 



The Decidua Parietalis 123 



The Decidua Capsularis 123 



