xiv LIST OF ILLUSTRATIONS. 



36. Wall of the Yolk-sac in the Region of the Area opaca of a Rabbit Embryo of Thirteen Days, ... 87 



37. Section of the Yolk-sac of a Young Human Embryo (a/?^r A'lf/^if/), 88 



38. Human Embryo, 2.15 mm. Long {after W. His), 88 



39. Human Embryo of 2. 6 mm. {after W. His), 89 



40. Human Embryo of 9.8 mm. Probable Age Thirty Days, 90 



41. Section of the Area vasculosa of a Chick Embryo of the Second Day, 92 



42. Development of Blood-corpuscles, ... 95 



43. Diagrams to Illustrate the Separation of the Embryo from the Yolk, , . 96 



44. Diagram of the Circulation in a Chick at the End of the Third Day, as Seen from the Under (Ento- 



dermal) Side, 98 



45. Area Vasculosa of a Rabbit, Presumably of about Twelve Days {after Van Beneden and Julin), 99 



46. Longitudinal Section of the Posterior End of a Sheep Embryo of Sixteen Days {after R. Bonnet), . loi 



47. Frog (Rana temporaria) Tadpole of 12.0 mm. Cross-section of the Pronephric Region {after M. 



Fiirbringer), I02 



48. Diagrams illustrating the Relations of the Allantois in Unguiculate Mammals, 104 



49. Pig, 15.0 mm., Series 135, Section 58, to Show the Relations of the Chorion to the Uterus, . . . 106 



50. Transverse Section of an Embryo Catfish (Amiurus) ; Series 25, Section 43, 108 



51. Sections of Two Human Umbilical Cords, 1 10 



52. Human Embryo at the Beginning of the Third Week, 114 



53. Two Diagrams to Illustrate the Hypothetical Early Development of Primates, 116 



54. Diagram of an Early Stage of a Primate Embryo, 117 



55. Semi-diagrammatic Outline of an Antero-posterior Section of a Human Uterus Containing an 



Embryo of about Five Weeks {after Allen Thompson), 1 19 



56. Human Uterus, about Forty Days Advanced in Pregnancy {after Coste), 120 



57. Blastodermic Vesicle of a Monkey (Semnopithecus nasicus) Attached to the Uterus ; Vertical Sec- 



tion {after E. Selenka), 1 22 



58. Embryo of the Preceding Figure More Highly Magnified {after E. Selenka), 123 



59. Section of Peters's Ovum in Situ {after H. Peters'), 124 



60. Embryo of a Gibbon (Hylobates concolor) in the Third Stage {after E. Selenka), 126 



61. Embryo of a Gibbon, Side View of the Embryo of Fig. 60 {after E. Selenka), . . 127 



62. Transverse Section of the Embryo of the Preceding Figure {after E. Selenka), 127 



63. Surface View of the Embryonic Area of the Ovum Shown in Fig. 61, 128 



64. Reconstruction of a Human Embryo 1.54 mm. Long {after Count Spee), 129 



65. Human Embryo of 1.54 mm. Median Section from a Wax Model Reconstructed from Sections 



{after Count Spee), 130 



66. Human Embryo of 1.54 mm. {after Count Spee), 130 



67. Human Embryo with Open Medullary Groove {after W. His), 131 



68. Human Embryo of from Thirteen to Fourteen Days {after J. Kallmann), I32 



69. Human Ovum, said to be from Fifteen to Eighteen Days Old, 133 



70. Embryo of Fig. 69, Separated from the Yolk-sac and Viewed from the Under Side, 134 



71. Human Embryo, 2.15 mm. 'Long {after IV. His), 135 



72. Reconstruction of the Anatomy of the Embryo Shown in Fig. 71 {after W. His), 136 



73. Human Embryo of 2.6 mm. Length {after W. His), 137 



74. Reconstruction of the Anatomy of the Embryo of 2.6 mm. in Fig.. 72 {after IV. His), 138 



75. Human Embryo, 4.2 mm. {after W. His), 139 



76. Outline of the Entodermal Canal of a Human Embryo of 4.2 mm. {after W. His), 140 



77. Reconstruction of the Anatomy of a Human Embryo, 3.2 mm. Long, showing the Anterior End 



Viewed from the Ventral Side, ... 140 



78. Reconstruction of the Anatomy of the Human Embryo of 4. 2 mm. Shown in Fig. 75 {after W. His), 141 



79. Human Embryo of About Twenty-three Days {after W. His), 142 



80. Human Embryo of 7 mm. {after E. P. Mall), 142 



81. Human Embryo of 7.5 mm. in Maximum Length {after W. His), 143 



82. Reconstruction of the Pharyngeal Region of a Human Embryo of 1 1. 5 mm. {after W. His), . . . 144 



83. Human Ovum with Embryo of 9.8 mm. The Chorion Has Been partly Removed to Show the 



Embryo {Minot Collection, ^yj), ^^45 



84. Embryo of the Preceding Figure, 146 



85. Human Embryo of II mm. {after JV. His), 147 



86. Human Embryo of about 14 mm., 147 



87. Human Embryo of about Thirty-five Days (a/?/fr Ci3j/if), 148 



88. Human Embryo of about 16 mm. {after W. His), 149 



89. Human Embryo of 22 mm., 150 



90. Human Embryo of 28 mm., , IS I 



V 



