94 RICHARD ASSHETON. 



Before explaining my figures on this point I must mention 

 the beautiful work of Cajal (3). 



The author, who made use of the Golgi and Weigert-Pal 

 method, describes the result of his observations on the optic 

 lobes of adult birds and of advanced embryos, amongst which 

 were chicks of the tenth day of incubation and upwards. 



Cajal finds that the great majority of the fibres of the optic 

 nerve end in the optic lobes, in many fine-branched twig-like 

 endings, but in no case do these endings anastomose or become 

 directly connected with nerve-cells. 



In an earlier paper (4) he described the termination of the 

 nerve-fibres in the retina as of two kinds. I quote from the 

 first-named paper (3), in which he on p. 338 gives a short 

 account of his previous work : 



" Dans cette membrane les fibres du nerf optique se termi- 

 nent de deux fa9ons ; par les cellules, c^est a dire, se con- 

 tinuant avec les cylindres-axes des elements de la couche 

 ganglionaire, et par des ramilles variqueueses et indepen- 

 dentes situees a la rencontre des couches reticulaire interne et 

 des grains internes. De ces deux especes de terminaisons, 

 seules les dernieres peuvent ainsi se qualifier, car les pre- 

 mieres ne sont point de veritables terminaisons, mais plutot 

 des origines de fibres dont la fin arborisee doit se trouver 

 dans le lobe optique. Si la doctrine de I'independance des 

 elements nerveux est certaine, le lobe optique devra nous 

 montrer, de meme que la retine, des cellules d'origine, et des 

 arborisations terminales.^^ 



Cajal (3), in what he calls the tenth layer (couche 10, 

 equivalent to the ninth granular layer of Stieda [24] and fifth 

 zone or zone fusiform cells of Bellonci [2] ), finds cells of an 

 ovoid or spherical shape with a protoplasmic expansion run- 

 ning inwards and outwards. The inward or inferior one seems 

 to end quickly, while the outer or superior runs outwards as 

 far as the layer of fibres of the optic nerve. From the latter 

 process arises an axis-cylinder which enters the layer of optic 

 nerve-fibres — couche 1 of Cajal. With reference to these 

 cells, and fibres arising from them, Cajal says on p. 248, — 



