HISTOLOGICAL ELEMENTS RETINA NECTURUS 421 
clearly set forth in table 4. I have taken the averages from five 
retinas in each ease, right and left eyes being used indiscrimi- 
nately. Twenty eyes were used, and in five cases counts from 
two different regions of the same eye were made, and in two 
cases right and left eyes from the same animal were considered. 
Averages per unit field for the right and left eyes respectively 
show a slightly greater number of rods and cones, and a smaller 
number of double-cones and doubtful elements in the left eye. 
These differences are shown in table 5. The maximum and 
minimum counts are, however, so close in every case as to lead 
me to believe that the number of elements involved in right and 
left sides is approximately the same, and I shall therefore make 
no discrimination between the two. 
TABLE 4 
Number of rods, cones, double-cones and uncertain elements in unit areas 
of 0.013 sq. mm. 
REGIONS OF THE EYEBALL IN WHICH THE UNIT AREAS WERE LOCATED 
DESIGNATION | 
OF Anterior Posterior Dorsal Ventral Fundus 
EYEBALLS 
BEC NED WEG 
R\C|-Di| Xt | Gael |e |e! le) exe Were ep ex 
Tr '46.039.5)12 
81 70.5/49.5114 | 0 (56.547.514 
16r 35.0/44.5121 | 0 
211 
221 49.2'41.0)14 | 2 
3r | 141.0187 |17 |0 
231 | 65.5\28.5| 10 | 6.037.531 |16 
4r | | 50.026 |20 | 2 
241 166.042.5125 | 0 
251 64.0/42.0] 8 | 9.5) 
6r 47.5147.014 |0 |59.0137.5119 | 1 | 
28r 50.5137.0/12 | 1 
3lr | 43.0142.515 | 4 |70.5/43.0| 5 
331 45.049.5) 18 | 2.5 
38 r 156.0/29.5|12 | 0 | | 
401 48.0\54.0/10 
56r 43. 5/38. 0\14 
57r 155.5141. 5/25 
59r 49.5136.5110 | 0.5 
601 40.5|28.0| 8 | 3 
| | 
_ 
)42.541.014 | 2 |52.5/46.5) 14 | 4.0 
o 
a 
i=) 
oo 
Average } | | | | 
of 5 Meee. 48. 2)43.1/17.80.4 |43.6/41 |11.8) 1.959.5/41.9) 11 | 5.2 46.236.215.8) 0.8 
retinas ) | | 
} | 
*R, rods; C, cones; D, double-:ones; X, uncertain elements; r, right eye; /, left eye. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 5 
