xvi LIST OF ILLUSTRATIONS, 



ma. PAGE 



11. Surface View of the Pellucid Area of a Blastoderm of i8 hours . 49 



12. Transverse Section of a Blastoderm incubated for 1 8 hours . . 51 



13. Transverse Section through the Dorsal Region of an Embryo of the 



Second Day .......... 55 



14. An Embryo Chick of the First Day (about thirty-six hours) viewed 



from below as a transparent object ...... 59 



15. Embryo of the Chioii at 36 hours viewed from above as an opaque 



object ....... ... . . 6r 



1 6. Diagrammatic Longitudinal Section through the Axis of an Embryo. 62 



17. A, B. Two consecutive Sections of a 36 hours Embryo illustrating 



the formation of the heart . . . . . . . .67 



iS. Transverse Section of an Embryo at the end of the Second Day 



passing through the region of bulbus arteriosus .... 68 



19. Surface View from below of a small portion of the posterior end of 



the pellucid area of a 36 hours Chick ...... 70 



20. Transverse Section through the Dorsal Region of an Embryo of 4^ 



hours 74 



21. Embryo of the Cliick at 36 hours viewed from above as an OjJaque 



Object 75 



22. Head of a Chick at the End of the Second Bay viewed from below 



as a Transparent Object ........ '76 



23. Diagram of the Circulation of the Yolk-Sac at the endof the Third 



Day of Incubation . . . ...... 85 



24. Chick of the Third Day (54 hours) viewed from underneath as a 



Transparent Object 88 



25. Head of a Chick of the Third Day viewed sideways as a Transparent 



Object ........... 90 



26. Section through the Hind-Brain of a Chick at the end of the Third 



Day of Incubation . . . . ... . . 9;:; 



27. Diagrammatic Sections illustrating the Formation of the Eye . . 97 



2S. Diagrammatic Section of the Eye and the Optic Nerve at an early 



stage 98 



