428 MALL. [Vol. VIII. 



method of staining. We have the three groups of ganglion 

 cells giving rise to nerves, two of which are situated within the 

 inner nuclear layer. In addition we have the bipolar cells, and 

 with Ramon y Cajal I can not wholly set aside the M tiller's 

 cells of the same layer, mainly on account of specimens obtained 

 by means of silver precipitation, and because of the mode 

 of development. In addition to the nerves arising from these 

 cells we have also no doubt centripetal nerves which have free 

 endings in the retina. This has been shown by means of 

 physiological experiment by Monakow,i by embryological ob- 

 servation by Martin ^ and by histological methods by Ramon y 

 Cajal.^ According to this last named author they end in the 

 inner nuclear layer of the retina. 



The three groups of ganglion cells of the retina giving rise 

 to the optic nerve, may be called, because of their location, 

 the inner, middle and outer ganglionic layers; the first lying 

 just beneath the outer granular, and the last just outside of the 

 layer of optic nerve fibers. In Necturus and Amblystoma the 

 middle group is the most prominent and sends large protoplas- 

 mic prolongation through the inner granular layer, as Fig. 1 1 

 shows. In addition to these cells there are cells lying just 

 inside of the outer granular layer, which also seem to give 

 rise to nerve fibers. As yet, however, I have been unable to 

 demonstrate that in its development the optic nerve arises in 

 part from the cells of the outer ganglionic layer of Dogiel. 



Shortly after the middle ganglionic layer begins to give rise 

 to the optic nerve fibers there appears a line of separation 

 between the middle and inner ganglionic layers, the beginning 

 of the inner granular layer. This rapidly increases in thick- 

 ness, and just before the retina is complete the outer granular 

 layer also makes its appearance. 



Before the retina is completed, its inner and outer borders 

 are defined by sharp lines formed by the many prolongations of 

 the spongioblasts, or Miiller's fibers. As the rods and cones 

 develop they perforate the outer border and come in contact 



1 Monakow, Arch. f. Psychatrie, Ed. XX. 



2 Martin, Zeit. f. Vergleich. Augenheilkunde, Bd. VII. 

 8 Ramon y Cajal, Anatom. Anz., 18S9. 



