180 RICHARD ASSHETON, M.A. 



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 M. 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, SP. 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. 



