HISTOLOGICAL ELEMENTS RETINA NECTURUS 429 
ina of average size should be about 167,000. This is a variation 
from the average estimates of two retinas of less than 5 per cent, 
which is negligible when we consider that the numbers in mini- 
mum and maximum retinas vary nearly 45 per cent of the former. 
Since Miiller’s fibers are regarded as merely supporting struc- 
tures and not a part of the nervous mechanism of the retina, they 
have been excluded from the final count of the nuclei properly 
belonging to the inner nuclear layer. The data for the inner 
nuclear layer of minimum, maximum, and average sized retinas 
are found in table 14. The extreme lower limit for the number 
of nuclei in this layer is approximately 97,000. 
TABLE 14 
Total numbers of nuclei of the inner nuclear layer in retinas of minimum, 
maximum, and average sizes 
(ole AS C4 a] i= 
og46 see | NUMBER OF NUCLEI PER OR 
, I = 3 2 | CYLINDER NUMBER OF NUCLEI z fe 
-& a n Z 
° Boog Dm Pusat aoa 
= ‘So ze | ] a 
Am < Pe a 1 be Se | = Oo, < 
Sa lnzas Boa a za4 
m3 Anna | BF Heo. | @g 5 
Ba Bm ao? ao — Le © Re Zu< 
> oe “a@q 5D sO nN | o oO Bm sl Aa 
na B24223) 5:6 g g o janes a] Se 2a 
<5 o8 S42) oka s = i AO o| SOQ <Dp 
a tage] 2Om Ca | ete 5 |,osan] as | faz 
& iS) iS} fon] | fon] < = (e) a 
WihtbbeNbied soe hAnooaec 9.7028 | 1243.948 | 121} 142 131 141,228 21,729 162,957 
With dbl lonlneoneenooone 14.0721 | 1804.115 121 142 131 203,667 32,672 236,339 
Averages of 14 retinas} 12.8034 | 1549.153 121 | 142 131 175,959 26,980 202,937 
f. Optic nerve fibers. As I have already said, the optic nerve 
was transected in two planes, viz., near its two ends, and the 
difference in the cross-sectional areas in these two regions was 
clearly established. When the fibers in the two regions were 
studied, those in the proximal portion seemed smaller and slightly 
more numerous to a unit area than in the distal portion. This 
led me to suppose that the total number of fibers was less prox- 
imally than distally, and my opinion was borne out by actual 
counts in the two regions in two optic nerves. Examination 
of other optic nerves indicated that similar numerical relations 
of the fibers existed in the two regions and was a characteristic 
feature of the optic nerve of Necturus. All counts were made 
on cross-sections of the optic nerves. Outline camera drawings 
(X 755) were made of cross-sections together with the nuclei 
