vm TABLE OF CONTENTS. 



CHAPTER III. 



The Changes which take place during the First Day of Ikcu- 



BATION . . . pp. 48 76. 



Variations in the progress of development, 48, 49. The embryonic 

 shield, 49. Formation of hypoblast, 51. The germinal wall, 52. 

 The primitive streak, 52 54. Formation of primitive streak meso- 

 bla^t, 54, 55. Hypoblastic mesoblast, 55. Primitive groove, 56, 57. 

 The notochord, 59 62. The medullary groove, 62, 63. Amnion, 63. 

 The changes taking place in the three layers, 63 66. The germinal 

 wall, 65, 66. The increase of the head-fold, 66. The closure of the 

 medullary canal, 66, 67. The cleavage of the mesoblast ; formation 

 of spanchnopleure and somatopleure, 68. The vertebral and lateral 

 plates, 69. The mesoblastic somites, 70. The sinus rhomboidalis, 71. 

 The neurenteric passage, 71 74. Formation of the vascular area, 

 74. 75- Recapitulation, 75, 76. 



CHAPTER IV. 



The Changes which take place during the First Half of the 



Second Day ... pp. 77 95. 



Increasing distinctness and prominence of embryo, 77. The first 

 cerebral vesicle, 78, 79. The auditory pits, 81. Increase in number 

 of mesoblastic somites, 81. The fore-gut, 82. The heart, 82 89. 

 The vascular system, 89 94. Formation of blood-vessels, 92 94. 

 The rudiment of the Wolffian duct, 94. Summary, 94, 95. 



CHAPTER V. 



The Changes which take place during the Second Half of the 



Second Day . . . pp. 96 108. 



Increasing prominence of the embryo; the tail-fold and lateral 

 folds, 96. Continued closure of medullary canal, 9698. The 

 braiti, 98101. The optic vesicles, 98. The second and third cerebral 

 vesicles, 100. The cerebral hemispheres, 100. First appearance of 

 cranial nerves, 100, loi. The notochord, loi. The cranial flexure, 

 loi. The auditory vesicle, loi. Increase of curvature of heart, loi. 



