• • • 



XV111 LIST OF ILLUSTRATIONS. 



FIG. PAGE 



47. Section through the Lumbar Region of an Embryo at tbe 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 Trabecuke on 



the Fourth Day of Incubation . . . . . . .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 . . . 181 



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



59. Section through the Spinal Corel of a Seven Days Chick . . 18S 



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 



O2. Diagram of the Venous Circulation at the Commencement of the 



Fifth Day 206 



6$. Diagram of the Venous Circulation during the later days of Incu- 

 bation ............ 20S 



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



mencement of Respiration by means of the Lungs . . .211 



65. State of Arterial Circulation on the Fifth or Sixth Day . . .212 



