CONTENTS ix 



CHAPTER XI 



PAGE 



The Effect of Injuring One of the First Two Blastomeres 106 

 Roux's Experiment of " Killing " One of the First Two Blasto- 

 meres. 

 Further Experiments by Others (Hertwig, Entires and "Walter, 

 Schultze, Wetzel, Morgan). 



CHAPTER Xn 



Interpretations of the Experiments; and Conclusions . . 123 

 Roux's Mosaic Theory of Development. 

 Theory of Driesch and of Hertwig of the Equivalency of the Early 



Blastomeres. 

 Roux's Subsidiary Hypothesis. 

 Experiments on Other Forms. 

 General Conclusions. 



CHAPTER XIII 



Organs from the Endoderm 137 



The Closure of the Blastopore, and the Formation of the Neuren- 



teric Canal. 

 The Digestive Tract and the Gill-slits. 



CHAPTER XIV 



Organs from the Mesoderm 146 



The Mesodermic Somites. 

 The Heart and Blood-vessels. 

 The Pronephros. 



CHAPTER XV 



Organs from the Ectoderm 159 



The Central Nervous System. 



The Eyes. 



The Ears. 



The Nerves. 



The Appearance of Cilia on the Surface of the Embryo. 



