xvi LIST OF ILLUSTRATIONS. 



fig. page 



1 1. Surface View of the Pellucid Area of a Blastoderm of 18 hours . 49 



12. Transverse Section of a Blastoderm incubated for 18 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 Chick at 36 hours viewed from above as an opaque 



object ..... . ... 61 



: 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 



1 3. 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 45 



hours ............ 74 



21. Embryo of the Chick at 36 hours viewed from above as an Opaque 

 Object 



/z> 



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



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



23. Diagram of the Circulation of the Yolk-Sac at the end 'of 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 . . . . . . . . -95 



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



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



stage 98 



