Viii CONTENTS 



Meroblastic Cleavage 44 



Superficial 44 



Discoidal 45 



References for Further Study 50 



CHAPTER VI 



GERM LAYERS 51 



The Two Primary Germ Layers Formation of the Gastrula 51 



Gastrulation in Amphioxus 51 



Gastrulation in Amphibians 52 



Gastrulation in Reptiles and Birds 57 



Gastrulation in Mammals 63 



Formation of the Middle Germ Layer Mesoderm 68 



Mesoderm Formation in Amphioxus 68 



Mesoderm Formation in Amphibians 72 



Mesoderm Formation in Reptiles and Birds 74 



Mesoderm Formation in Mammals 81 



The Germ Layers in Man . 85 



References for Further Study 92 



CHAPTER VII 



FCETAL MEMBRANES 95 



Foetal Membranes in Birds and Reptiles 95 



The Amnion 95 



The Yolk Sac 99 



The Allantois . 102 



The Chorion or Serosa 103 



Foetal Membranes in Mammals 103 



Amnion, Chorion, Yolk Sac, Allantois, Umbilical Cord 104 



Further Development of the Chorion. 107 



The Fcetal Membranes in Man in 



The Amnion m 



The Yolk Sac 113 



The Allantois 114 



The Chorion and Decidua 115 



The Decidua Parietalis 119 



The Decidua Capsularis 119 



The Decidua Basalis 120 



The Umbilical Cord 128 



The Expulsion of the Placenta and Membranes 130 



Anomalies !3o 



References for Further Study 131 



