216 
HENRY LAURENS AND S. R. DETWILER 
Relative distribution of rods and cones. In the upper peripheral 
portion of the retina there are very few cones. In the region 
designated by A (fig. 1), the ratio of rods to cones is about 
95:5. The cones in this region, mostly single and of the large 
type, are irregularly distributed. In the typical tapetal portion 
(fig. 1, B) they are slightly more numerous (about 15 per cent). 
The majority of the cones, however, in this region are double, 
unlike those from the more peripheral portion of the retina. As 
the optic nerve is approached the number of cones shows a 
corresponding increase. In the region designated by C (fig. 1) 
TABLE 1' 
DISTANCE FROM 
NUCLEUS TO 
OUTER SEGMENT 
IN^! 
DISTANCE FROM 
NUCLEUS TO 
ELLIPSOID IN fX 
DISTANCE FROM NUCLEUS 
TO P.^RABOLOID IN fl 
DISTANCE FROM 
ROD NUCLEUS 
TO NEAREST 
Cones 
Rods 
Cones 
Rods 
Single 
cones 
Double cones 
NEEDLE IN fl 
Large 
Small 
Dark 
19.8 
17.6 
13.5 
17.5 
14.5 
12.1 
7.5 
11.5 
6.8 
4.7 
6.7 
4.0 
13.0 
9.5 
11.5 
Light 
9.9 
Difference 
2.2 
4.0 
2.4 
4.C 
2.1 
2.7 
3.5 
1.6 
1 Total number of rod measurements, 280. 
Total number of cone measurements, 190. 
Total number of pigment measurements, 60. 
Measurements made at about 2 to 3 mm. distance from the entrance of the 
optic nerve, in the region designated by C in figure 1, with the exception of the 
measurements of double cones which were taken from region B. 
approximately 40 per cent of the visual cells are cones. Here 
the double cones are still more numerous than the single cones. 
In the guanin-free portion above the optic nerve (fig. 1, D) 
cones and rods are about equal in number, the single cones again 
exceeding in number the double. The cones outnumber the 
rods in the lower portion of the retina, the number increasing 
from the region of the optic nerve toward the ora serrata, and 
including all types. In this region only a few scattered rods are 
present. About 75 per cent of the cones in this region are single, 
the majority of which are like that shown in figure 5. The 
small type (fig. 6) is relatively scarce. 
