Illustrations xiii 



FIGURE PAGE 



38. A B C D Diagrams Illustrating the De- 



velopment of the Foetal Membranes of a 

 Bird. (After Parker and Haswell) . 117,118 



39. Part of a Section through the Blastoderm after 



the Formation of the Definite Entoderm or 

 Hypoblast. (After Duval) . . .121 



40. Surface View of the Embryo at about the Six- 



teenth Hour of Incubation. (After Duval) 122 



41. Median Portion of a Transverse Section of an 



Embryo at the Time of Formation of the 

 Primitive Streak. (After Duval) . .124 



42. Transverse Section of an Embryo of about 



Twenty-one Hours, through the Anterior 

 Part of the Medullary Folds. (After Duval) 126 



43. Three Transverse Sections across the Caudal 



End of the Medullary Groove of a Chick 

 Embryo with Seven Segments. (After 

 Minot) 128 



44. Surface View of Embryo at the Twenty-third 



Hour of Incubation. (After Duval) . .129 



44A. Anterior End of the Preceding Figure, More 

 Highly Magnified to Show the Details. 

 (After Duval) 131 



45. Sagittal Section of an Embryo of Twenty-six 



Hours. (After Duval) .... 133 



46. Diagrammatic Representations of Chick Em- 



bryos: A after Twenty Hours' Incuba- 

 tion; B after Twenty-four Hours' Incuba- 

 tion. (After Parker and Haswell from 

 Marshall) 136 



