HISTOLOGICAL ELEMENTS RETINA NECTURUS 423 
To correlate the number of visual cells with the number of 
nuclei in the outer nuclear layer, it was necessary to count each 
double-cone as two units, on the assumption that each double- 
cone has two nuclei. This view is held by Howard (’08), who 
found two nuclei associated with each double-cone in macerated 
material. My own observations on sectioned material confirm 
this relation. The proportions of rods to cones and to double- 
cones approximates 3.5 : 2.8 : 1, respectively, which is a decided 
increase in the relative number of cones over that given by 
Howard. | 
b. Outer nuclear layer. The outer nuclear layer, when exam- 
ined in radial sections of the eye (figs. 1 to 4) was seen to consist 
of a complete single externa! row of nuclei with here and there 
additional nuclei lying directly against its inner side. In cal- 
culating the number of nuclei in the ‘external’ sheet of which 
the ‘single row’ is the section, I have used the method already 
employed for the visual cells. The numbers of nuclei per unit 
area in the external sheet are given in table 8. In the fundus 
the numbers are slightly less than in the other regions. In order 
to include the partial ‘internal’ sheet in my enumerations, I 
counted the nuclei in the external and internal rows in median 
sections from periphery to periphery in eight retinas. In the 
TABLE 7 
Total numbers of visual cells in retinas of minimum, maximum, and average sizes. 
The enumerations are based on the following average numbers of elements in a unit 
field of 0.065 sq. mm. area: rods, 255.4; cones 204.1; double-cones, 72.2; uncertain 
elements 8.7; total visual cells, 540.4 (table 6) 
Eee 
lnzaZa 2 
}4q Deg < Z 
8 <n ahi TOTAL NUMBER OF 
i= z & 5 3 S 2 
RELATIVE SIZE |g 3 QP a 
OF EYEBALLS |8m 5 < On = = ee z = ee == 
Hd 4 oe} m | 
azpad es 
agae 8 Qa 
|PHQR= ag ; Double- | Uncertain! Visual 
Ae } 
| SBS a sa] I B Rods Cones cones elements | cells 
ls z | 
oes | | | - ‘ od 
Minimum... .| 10.8184 | 166.437 | 42,508 33,970 12,017 | 1,448 89,943 
Maximum....| 15.1777 | 233.503 | 59,637 | 47,658 16,859 | 2,032 
126,185 
Average of 14 
retinas..:..| 13.4698 | 207.228 | 52,926 | 42,295 14,962 | 1,803 111,986 
