PEALE 
Figures 26-31, 37, from the frog; Figures 32-36, from Necturus. 
Figures 26 to 31 are magnified 1,300 diameters; Figure 32, 1,450 
diameters; Figure 33, 900 diameters; Figure 34, 3,800 diameters: and 
Figures 35-37, 1,000 diameters. 
Fic. 26.—Outline drawing of visual cells from the frog retina in situ. 
The outer nuclear layer is two nuclei deep. In the red rods the inner 
segments are short; in the green rods the myoid portion of the inner 
segments is long. The cones are much smaller than the rods and 
contain an oil globule between the outer segment and the ellipsoid. 
The material was fixed in Perenyi’s fluid and stained with Heiden- 
hain’s iron-alum-hzmotoxylin. 
Fic. 27.—A single rod from the group shown in Figure 26. Detail 
is shown at the distal end of the outer segment and over the whole 
of the inner segment. Longitudinal peripheral fibrils are visible on 
the outer segment over the intermediate plate and on the myoid of 
the inner segment. 
Fic. 28. Cross sections of outer segments of the same material as 
that shown in Figures 26 and 27. A central axial portion is differentiated 
from the peripheral part. The latter is subdivided by lines which cor- 
respond in number with the longitudinal fibrils on the surface. 
Fic. 29.—A red rod from a radial section of the retina of a frog. 
An axial core is visible in the whole outer segment. In the inner limb 
is a body corresponding to the paraboloid in Necturus. The material was 
fixed in corrosive-acetic mixture and stained in Heidenhain’s iron-alum- 
hematoxylin and orange G. 
Fic. 30—Cross section of the outer segment of a rod from the 
same material as that shown in Figure 209. 
Fic. 31——A green or short rod from the frog as seen in a radial 
section of the retina including the pigment layer. The fixation is the 
Same as for the preparation shown in Figure 29; the preparation was 
stained with fuchsin. 
Fic. 32—Visual cell of Necturus fixed in vom Rath’s fluid. 
The outer segment is very much blackened and contracted. In a 
thin section the longitudinal grooving appears as light lines in the dark 
substance of the outer limb. 
Fic. 33.—Rod and cone cells of Necturus fixed five minutes in osmic 
acid fumes and isolated in glycerine. 
The individuality of the cells is demonstrated. The osmic acid has 
induced rather forcible contraction of the inner segments and the cleav- 
age in the outer segments of the cone is excessive. 
Fic. 34.—Cross section of the outer segment of a Necturus rod, 
fixed in osmic acid fumes and seen under high magnification. The 
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