458 J. GEAnAM KKKR. 



n. Stage 31. 

 E. Stage 31 -|-. 

 r. Stage —35, 

 G. Stage 3S. 

 11. Stage 39. 



I. Adult. 



oc. Eye nidimciit. Other letters as in Figs. S and 9. 



Fig. 11. — Illustrating the development of the eye. All the figure s illus- 

 trating the development of the eye arc taken from sections transverse lo the 

 long axis of the head. 



A. Stage 21. Zfiss A, oc. 2. 



ih. Still solid thalamencophalon ; oc. Eye rudiment. 



B. Stage 23. Zeiss A, oc. 2. A cavil.y is now arising in the optic 



rudiment ; the brain is still solid in this region. 



c. Stage 25. Zeiss A, oc. 4. Thalamenceplialon and optic vesicle are 

 now hollow. The retinal wall of the optic vesicle is beginning to 

 thicken. 



D. Stage 26. Zeiss A, oc. 2. Showing advanced thickening of 



retina. 



E. Stage 30. Zeiss A, oc. 4. Optic cnp — lens rudiment with com- 



mencing cavity {I.e.). 

 E. Stage 31. Zeiss D, oc. 2. 

 G. Stage 35. Zeiss A, oc. 4. 



II. Stage 38. Zeiss A, oc. 4. 



PLATE 28. 



Fig. 11, I— N. Illustrating tlie development of the percipient elements. 



I. Stage 35. J^ liom. imm,, comp. oc. 0. Showing the formation 



of the fatty globules and their passage into pocket-like projec- 

 tions of the internal limiting membrane. 



Off. Globule; p. Pocket; m.l. Membrana limitans ; nu. 

 Nucleus of visual cell. 

 J. Stage 35. -^i^ horn, imm., comp. oc. (5. Showing first rudiment of 



rod as a protoplasmic projection (;•.). 

 K. Stage 35. ^2 ^°"'' i'ii"i-) comp. oc. 6. Sliglitly later stage of 



rod development. 

 L. Stage 35. -j^^ hom. imm., comp. oc. 6. Rod showing first signs 



of stratification. Appearance of annular vacuole {a.v.). 

 M. Stage 38. -^.^ horn, imm., comp. oc. G. A fully formed rod 



element, fixed in the light. 

 N. A similar rod element from a young Lepidosiren of the same age 



and same brood, but fixed in the dark. 



