DEVELOPMENT OF THE OPTIC NERVE OF VERTEBRATES. 179 



21. ORR. — "Contribution to the Embryology of the Lizard," 'Journal of 



Morphology,' vol. i, No. 2, 1887. 



22. ORR. — " Note on the Development of Amphibians," 'Quart. Journ. Micr. 



Sci.,' vol. xxix, 1887. 



23. SCHAFER.— " Embryology," Part 1 of vol. i of ' Quain's Elements of 



Anatomy,' 10th edition, 1890. 



24. STIEDA. — "Studien uber das centrale Nervensystem der Vogel und 



Saugethiere," ' Zeits. f. wiss. Zool.,' Bd. xxx, 1868. 



25. SPENCER, W. B.— " On the Presence and Structure of the Pineal Eye in 



Lacertilia," 'Quart. Journ. Micr. Sci.,' 1886. 



EXPLANATION OF PLATES VIII. & IX. 



Illustrating Mr. Richard Asshetou's paper "On the Development 

 of the Optic Nerve of Vertebrates and the Choroidal Fissure 

 of Embryonic Life," 



Alphabetical List of Reference Letters for all the Figures. 



BR. Brain. B. V. Blood-vessel. C. Cone. C. OP. V. Cavity of the optic 

 vesicle. CH. Choroid fissure. CH'. Choroid fissure, outer end. D. Growing 

 rim of optic cup. FR. Radial fibres. G. Cells of the ganglionic layer of the 

 retina. L. Lens. L. C. Cavity of lens. M. COM. Middle commissure. 

 MES. Mesoblastic sheath round optic nerve and stalk. MO. Outer molecular 

 layer. N. Neuroblast. NI. Inner nuclear layer. O.P. N. Optic nerve. 

 OP, RG. Optic recess. OP. S. Optic stalk. OP. S'. Cells of optic stalk 

 separated. P. Pigment layer of retina, i.e., posterior wall of optic vesicle. 

 R. Rods. R. CH. Edge of choroid fissure. RS. Rim of optic cup. TR. CR. 

 Trabecula cranii. X. Neuroblast of inner nuclear layer. 



Fig. 1. — Horizontal section of the right eye of a 10 mm. tadpole, 



Fig. 2. — From a horizontal section of a 10 mm. tadpole. In this the optic 

 stalk OP. S., and optic nerve OP. N., are cut across transversely to their 

 length. 



Fig. 3. — From a horizontal section of a 10 mm. tadpole. The optic nerve and 

 optic stalk are seen separating at their junction with the brain. 



Fig. 4. — From a sagittal section of a 7 mm. tadpole. The figure shows the 

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

 through the choroidal fissure. 



Fig. 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. 



