426 



MALL. 



[Vol. VIII. 



From another standpoint it was also shown by Froriep ^ 

 that the first fibers of the optic nerve must arise from the 

 retina, because he found in a shark embryo an optic nerve 

 arising from the retina but not reaching to the brain. The 

 same has been shown to be true by Keibel ^ and by Assheton.^ 

 In both Figs. 9 and 10, which arc from Amblystoma and 

 Necturus respectively, the optic nerve arises from deeper 

 portions of the retina as well as from the ganglian-cell layer. 

 Especially in Necturus is this second growth of cells, which 



Fig. II. — Section through the optic nerve and retina of Necturus two and one- 

 half months old. Hardened in picro-chromic and osmic acids. X 550 times. 



give rise to optic nerve fibers, well marked. In later stages, 

 as soon as the inner granular layer is well formed, these 

 large cells send a single protoplasmic prolongation almost 

 through the granular layer a give rise to a single nerve fiber 

 which can with the greatest of ease be followed into the optic 

 nerve. Fig. 1 1 is a picture of a specimen which had been 



1 P'roriep, Anatom. Anz., 1S91. 



2 Keibel, Sitzungsber. d. Nat. Med. Vereins, 1888. 



3 Assheton, Quarterly Jour, of Microscop. Science, 1892. 



