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 of 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 of the Entoderm 20 



The morula stage; the formation of the blastula; 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 S3 

 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. 



