CONTENTS 



PAGE 

 PREFACE v 



CHAPTER I 



INTRODUCTION i 



CHAPTER II 



THE GAMETES AND FERTILIZATION 7 



The ovarian ovum; maturation, ovulation, and fertilization; the 

 formation of the accessory coverings of the ovum; the structure of 

 the egg at the time of laying; incubation. 



CHAPTER III 



THE PROCESS or SEGMENTATION 14 



The effect of yolk on segmentation; the unsegmented blastodisc; the 

 sequence and orientation of the cleavage divisions in birds. 



CHAPTER IV 



THE ESTABLISHMENT OP THE ENTODERM 20 



The morula stage; the formation of the bias tula; the effect of yolk on 

 gastrulation; gastrulation in birds. 



CHAPTER V 



THE FORMATION OF THE PRIMITIVE STREAK AND THE ESTABLISHMENT OF 



THE MESODERM 27 



The location and appearance of the primitive streak; the origin of the 

 primitive streak by concrescence of the blastopore; the formation of 

 the mesoderm. 



CHAPTER VI 



FROM THE PRIMITIVE STREAK STAGE TO THE APPEARANCE OF THE SOMITES 33 

 The primitive streak as a center of growth; the growth of the entoderm 

 and the establishment of the primitive gut; the growth and differ- 

 entiation of the mesoderm; the formation of the notochord; the forma- 

 tion of the neural plate; the differentiation of the embryonal area. 



CHAPTER VII 



THE STRUCTURE OF TWENTY-FOUR HOUR CHICKS 44 



The formation of the head; the formation of the neural groove; the 

 regional divisions of the mesoderm; the coelom; the pericardial region; 

 the area vasculosa. 



