EXPLANATION OF FIGURES 
The drawings are all from Necturus maculosus (Raf.) All the outlines in figs. 
1 to 12 were made with the aid of the camera lucida. The sections of the retina 
were stained in Heidenhain’s iron haematoxylin followed by a 70 per cent alco- 
holic solution of eosin. Radial sections of the visual cells (figs. 1 to 4) were cut 
8u thick, and cross-sections (figs. 5 to 9) 6u thick. 
The optic-nerve fibers were stained in Bielschowsky’s fluid in every case, and 
all sections were 5y thick. 
Fig. 1 Semi-diagrammatic drawing of a radial section of a normal retina of 
Necturus; cd, xz, vw designate three zones in which the areas of the retinas were 
obtained; ab, mn, xz and vw designate the ‘levels’ in which average counts, per 
unit areas, were obtained for the different layers of the retina. X 331. 
Fig. 2. Semi-diagrammatic drawing of a radial section of a retina with two 
sublayers or ‘sheets’ in the inner nuclear layer. n, horizontal cell. X 331. 
Fig. 3 Semi-diagrammatic drawing of a radial section of a retina with four 
to five sublayers in the inner nuclear layer. mn, horizontal cell. X 331. 
Fig. 4 Semi-diagrammatic drawing of a radial section of a retina with two 
nuclei, m, of Miiller’s fibers, in the outer nuclear layer. X 331. 
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