EXPLANATION OF THE FIGURES. 



Fig. I. — Chick, ist day, showing at A A the primary 

 optic vesicles. 



Fig. 2. — Chick, 2d day. Thickening of external epi- 

 blast to form lens. 



Fig. 3. — Chick, 3d day. Formation of lens-sac and 

 secondary vesicle. 



Fig. 4. — Rabbit, sagittal section. Lens-sac fully 

 formed. 



Fig. 5. — Rabbit ; early vitreous ; x 200. 



Fig. 6. — Chick ; lens fully formed. 



Fig. 7. — Pig, 4 cm. long ; horizontal section. 



Fig. 8. — Pig, 4^ cm. long ; horizontal section. 



Fig. 9. — Pig, 6 cm. long ; horizontal ; ant. segment. 



Fig. 10. — Pig, 6 cm. long ; horizontal ; post, segment. 



Fig. II. — Pig, about 9 cm. long ; horizontal ; ant. seg- 

 ment. 



Fig. 12. — Pig, 9 cm. long; horizontal; post, segment. 



Fig. 13. — Pig, 12.5 cm. long ; horizontal. 



Fig. 14. — Retina pig ; A, ganglion-cells ; B, pale cells. 



Fig. 15. — Retina pig near term ; A, ganglion-cells ; B, 

 reticular layer ; C, layer of pale cells. 



68 



