438 SAMUEL C. PALMER 
eye, and the fallibility of the stain must be given due weight. 
I am unwilling to make any statement as to the origin of the 
optic nerve fibers in Necturus, and await with interest further 
investigation of this subject by other methods. 
VII. SUMMARY 
1. The proportion of rods to cones is about the same in all 
regions of the retina. Double-cones are wanting at the extreme 
periphery. 
2. There is no particular plan of arrangement of the visual 
cells. 
3. In the retina of average size there are about 110,000 visual 
cells, of which 53,000 are rods, 42,000 cones, and 15,000 double- 
cones. 
4. The total number of visual cells varies with the size of the 
retina. In maximum sized retinas the number of visual cells 
is about 126,000; in minimum sized retinas, about 90,000. 
5. The number of visual cells is less than the number of nuclei 
in the outer nuclear layer. 
6. The total number of nuclei in the outer nuclear layer in 
an average-sized retina is 121,000. The number varies from 
137,000 in maximum sized retinas to 97,000 in mimimum sized 
retinas. 
7. The outer nuclear layer consists of two sheets; an external 
complete, and an internal loosely scattered sheet, with 94,000 
and 27,000 nuclei, respectively, in the average-sized retinas. 
8. The nuclei of the internal sheet’ of the outer nuclear layer 
consists of nuclei of the visual cells, of Miiller’s fibers, and possi- 
bly of horizontal cells. 
9. The inner nuclear layer is the most variable of all the layers 
in the number of its elements. In an average sized retina there 
are approximately 176,000 nuclei in a layer composed of three 
sub-layers. The range in the number of nuclei in maximum and 
minimum retinas of this structure is 204,000 to 45,000. 
10. The inner nuclear layer may have as many as five sub- 
layers or as few as two. 
