XVIU LIST OF ILLUSTRATIONS. 



FIG. PAGE 



47. Section through the Lumbar Region of an Embryo at the End of 



the Fourth Day . . -144 



48. A. Head of an Embryo Chick of the Fourth Day viewed from 



below as an opaque object. B. The same seen sideways . . 146 



49. Longitudinal Section of the Tail-end of an Embryo Chick at the 



commencement of the Third Day .148 



50. Longitudinal Section of the Tail-end of an Embryo Chick at the 



middle of the Third Day . . . . . . . .149 



51. Section of the intermediate Cell-mass on the Fourth Day . . 165 



52. State of Arterial Circulation on the Fifth or Sixth Day . . . 169 



53. Diagram of the Venous Circulation at the Commencement of the 



Fifth Day 170 



54. Heart of a Chick on the Fourth Day of Incubation viewed from 



the Ventral Surface 172 



55. View from above of the Investing Mass and of the Trabeculae on 



the Fourth Day of Incub£,tion . . , . . . .177 



56. A. Head of an Embryo Chick of the Fourth Day viewed from 



below as an opaque object. B. The same seen sideways. . 180 



■57. Head of a Chick at the Sixth Day from below . . . . iSi 



58. Head of a Chick of the Seventh Day from below .... 182 



59. Section through the Spinal Cord of a Seven Days Chick . .188 



60. Two views of the Heart of a Chick upon the Fifth Day of Incuba- 



tion ... . . . ... . ..192 



61. Heart of a Chick upon the Sixth Day of Incubation, from the 



Ventral Surface .......... 193 



62. Diagram of the Venous Circulation at the Commencement of the 



Fifth Day 206 



63. Diagram of the Venous Circulation during the later days of Incu- 



bation ........... 308 



64. Diagram of the Venous Circulation of the Chick after the com- 



mencement of Eespiration by means of the Lungs . . .411 



65. State of Arterial Circulation on the Fifth or Sixth Day . . . 2i2 



