104 EICHARD ASSHETON. 



the ventral edge of the posterior part of the eyeball ; the optic nerve is seen 

 passing through the choroidal fissure. 



EiG. 5. — From the same series as Fig. 4, taken nearer to the brain. 7 mm. 

 tadpole. 



Fig. 6. — From the same series as Figs. 4 and 5, taken about midway 

 between eye and brain, nearer to brain than Fig. 5. 7 mm. tadpole. 



Fig. 7. — From the same series as Figs. 4, 5, and 6, taken still nearer to the 

 brain. 



Fig. 8. — From a sagittal section of a 23 mm. tadpole, taken near to the 

 brain. Optic nerve and optic stalk cut transversely. 



Fig. 9, — From a sagittal section of a 23 mm. tadpole, as Fig. 8. 



Fig. 10. — Same as Figs. 8 and 9, but taken nearer to the eye. 



Fig. 11. — From a transverse section of a 23 mm. tadpole. The optic nerve 

 is cut " sagittally ;" the cells of the broken-up optic stalk are seen scattered 

 over it. 



Fig. 12. — Semi-diagrammatic figure of a solid section of an eye of an 8 mm. 

 tadpole. The optic nerve-fibres are seen on the cut surface to be processes 

 of neuroblasts (blue). They pass over the ventral edge of the optic cup (the 

 choroidal fissure). The edge of the choroidal fissure is seen at R. CH, the 

 mosaic-like pattern being the pigment-cells of the hinder wall of the optic 

 vesicle. The optic stalk is seen to be hollow, and quite separate from the 

 optic nerve. The cells of the walls of the optic stalk pass into the pigmented 

 cells of the outer wall, and the spongioblasts of the inner wall of the optic 

 cup, HP. The blood-vessel which enters the optic cup is seen cut off at B. V. 



Fig. 13. — A section of the retina of a 13 mm. tadpole. A description of 

 this figure is given in the text. Prep. Perenyi's fluid; aniline blue-black. 



