418 SAMUEL C. PALMER 
of my measurements are given in table 3. Hight retinas were 
measured in the antero-posterior and six in the dorso-ventral 
plane. Variations in the thickness of the retinas (figs. 2 to 4), 
measured from visual cells to internal limiting membrane, and 
irregularities of the retinas, especially at the periphery, are the 
causes of the differences of area in retinas nos. 3 and 8, 5 and 6, 
and 10 and 14. 
In order to enumerate the retinal elements, it was necessary 
to adopt unit areas small enough to avoid the distortion at the 
margin of the microscopic field and large enough to include a 
great number of elements. Convenient sizes were found in a 
circular area of 0.013 sq. mm. for the visual cells and one of 0.0078 
sq. mm. for the other elements. The areas of the retina in the 
zones at the different levels were duly considered, so that the 
number of visual cells and nuclei of the outer nuclear layer was 
TABLE 3 
Calculated areas of zones corresponding to the area of the retina in Necturus and 
passing through (1) the external limiting membrane, (2) the middle of the inner 
nuclear layer, and (8) the ganglionic layer 
| AREAS OF ZONES IN SQUARE MILLIMETERS AT THE 
ESIGN? IN - 
VTSARC ENE MNOES PLANES OF SECTIONS | = 
D282 | External limiting Middle of inner Middle of the 
| | membrane | nuclearlayer | ganglionic layer 
1 Antero-posterior. . | 12.5664 | 11.7094 10.9073 
2 ‘Antero-posterior. . | 13.4484 | 11.8309 10.3138 
3 |Antero-posterior. . | ila beara | 13.5815 | 12.0693 
4 \Antero-posterior. . 13.8940 | 12s 2255 10.6535 
5 |Antero-posterior. 15.0399 | 13.6455 12.3176 
6 ‘Antero-posterior. . | 15.0399 | 13.8940 12.8165 
ii Antero-posterior. .| 12.0693 10.9133 | 9.8120 
8 Antero-posterior. . 15.1777" || LA OT2T I NS une ne 
9 Dorso-ventral..... | 14.6303 12.1947 | 9.9743 
10 ‘Dorso-ventral..... | 10.8184} 9.70287 8§.6916F 
1] Dorso-ventral....., 12.5664 11.4616 10.4257 
12 Dorso-ventral..... 13.2541 11.8005 10.4257 
13 ‘Dorso-ventral..... | 13.9602 12.3796 10.9073 
14 Dorso-ventral..... 10.9351 9.7569 | 8.6916F 
Average areas of zones in square 
MMMM CCIE: 126 eee ses 13.4698 12.0834 10.7910 
* Maximum areas 
+ Minimum areas 
