viii CONTENTS 



CHAPTER V 



PAGE 



Early Development of the Embryo 50 



The Blastopore. 



External Changes after the Closure of the Blastopore. 



CHAPTER YI 



Formation of the Germ-layers 63 



His's Experiments with Elastic Plates. 

 The Formation of the Embryo by Concrescence. 

 The Formation of the Archenteron. 

 The OvergTowth of the Blastoporic Rim. 

 The Origin of the Mesoderm. 



Different Accounts of the Origin of the Archenteron and Meso- 

 derm. 

 Later Development of the Mesoderm and Origin of the Notochord. 



CHAPTER VII 

 The Production of Abnormal Embryos with Spina Bifida . 75 



CHAPTER VIII 



Pfluger's Experiments on the Frog's Egg 81 



The Effect of Gravity on the Direction of the Cleavage. 



The Relation of the Planes of Cleavage to the Axes of the 



Embryo. 

 Conclusions from the Experiments. 



CHAPTER IX 



Experiments of Born and of Roux 90 



Changes that take Place in the Interior of the Egg after Rotation. 

 The Cleavage of the Egg in a Centrifugal Machine. 



CHAPTER X 



Modification of Cleavage by Compression of the Egg . . 95 



Effect of Compressing the Segmenting Egg between Parallel Plates. 



Conclusions from the Experiments. 



The Distribution of the Nuclei in the Compressed Egg. 



