CONTENTS. 



PAGE. 



Introduction 215 



Methods 217 



Methods of nutrition of early embryos 220 



Appearances of the exoccelom in the living blastoderm 222 



Differential ion of angioblasts from mesoderm 227 



Method of formation of blood-vessels from solid angioblasts 231 



Origin of blood-islands 236 



Cycles in the development, of the vascular system 241 



Cycles in cell division 252 



Origin of the heart and aorta 255 



Conclusions 256 



Bibliography 257 



Explanation of plates 259 



214 



