434 SAMUEL C. PALMER 
I have called attention to the three-layer condition of its nuclei 
as the most characteristic condition, but two or four layers were 
not uncommon. Ramén y Cajal (94) points out that the inner 
nuclear layer of amphibians consists of a number of ‘types’ of 
both amacrine and bi-polar cells, but I have made no attempt in 
this study to distinguish between them, and have considered 
the layer merely as a whole. Though the results obtained cannot 
be adapted to every retina because of the great individual varia- 
tion, I am convinced that they are as accurate as possible for the 
three-layered average sized zone. 
The ganglion-cell layer presents few features of special note 
in connection with the number of its nuclei. It consists uniformly 
of a single layer of loosely associated, large nuclei. A consider- 
ation of vital importance is the failure of Bielschowsky’s impreg- 
nation method to demonstrate a union between the ganglion 
cells and the optic nerve fibers. Just what the real significance 
of this is, I am unable to say, and, when considered in relation 
to the number of optic nerve fibers in proximal and distal parts 
of the optic nerve, the interpretation becomes even more difficult. 
Enumerations of the cross-sections of the strands of Miller’s 
fibers per unit area in the inner reticular layer gave better results 
than enumeration of their nuclei per unit area in the inner nuclear 
layer, because at the plane of sectioning in the reticular layer 
there is no other structure with which they might be confused; 
secondly, the fibers stand out clearly in cross-section, and each 
fiber may be supposed with reasonable certainty to represent 
a complete unit; and, lastly, the chance of missing even a single 
fiber in the unit areas, was very small. 
The objections to using the nuclei as a means of enumeration 
lie in the difficulty of distinguishing the nuclei of Miiller’s fibers 
from other nuclei in the layer; and secondly, in the fact that 
the nuclei of Miiller’s fibers are not always found within the 
limits of inner nuclear layer (fig. 4), in which case it would be 
impossible to count with certainty all the cells in a given field. 
Enumerations of the optic nerve fibers were more tedious than 
difficult. The black ends of the fibers contrasted sharply with 
