XV i LIST OF ILLUSTRATIONS. 



FIG. 



11. Surface View of the Pellucid Area of a Blastoderm of 18 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 , . : , . V . * ... V, . 55 



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



from below as a transparent object . '. '. ' A , . ... 59 



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



object . . ..''.. 6 1 



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 



1 8. 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 , . ' ' 75 



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 i . . . 88 



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



Object . ' s . . . . .... . 90 



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



Day of Incubation . . . . . . * : 'i .-... . * jr 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 .... ' ....,', *';*''.;. ,' .'. ' ,f V ,t . 4* 98 



