46 



BLIND VERTEBRATES AND THEIR EYES. 



out, while the outer portion is longer and somewhat triangular in shape, with the 

 smaller side of the triangle resting on the inner elliptical part. This layer measures 

 10 /* in depth, while the same layer in Anolis measures 13 p. 



The Outer Nuclear Layer. — This layer is made up of a single stratum of nuclei 

 with small dark nucleoli (3, fig. 15 a). Some of these nuclei are almost spherical, 

 while others are oval in shape. They are connected with the cones by broad pro- 

 cesses which stain darkly. These processes may be very short, in which case the 

 cone comes in close proximity to the nucleus; or they may be drawn out into fila- 

 ments as long as or longer than the nuclei themselves. From the inner part of the 



nuclei extend processes which broaden toward the base and 

 send numerous ramifications into the inner stratum of the 

 outer reticular layer. There is a striking difference here 

 between this eye and the normal one. The processes from 

 the base of the nuclei pass straight through the outer reticu- 

 lar layer, while in certain sections of the normal eye they 

 pass through at an angle of about 45 (3, fig. 15 b). 



The Outer Reticular Layer. — The outer reticular layer 

 (4, fig. 15 a) is penetrated by the processes from the nuclei 

 of the outer nuclear layer and by a few Mullerian fibers. 

 If processes from horizontal cells are present, they were 

 not brought out by the method of staining which was used. 

 Again, there is but little difference in the thickness of this 

 layer in the two eyes, as it measures 6 /a in Amphisbcena 

 and 7 ^ in Anolis. 



The Inner Nuclear Layer. — The inner nuclear layer 

 is a compact mass of somewhat irregular spherical nuclei 

 and is 24 /x in thickness (6, fig. 15 a). The corresponding 

 layer in Anolis is 59 /a. Spongioblast and bipolar cells can 

 not be differentiated from each other. All of the nuclei 

 appear to be very much alike, except the nucleated en- 

 largements of the fibers of Muller, which have no definite 

 shape and which stain very densely. However, some nuclei, 

 more especially those of the inner stratum, stain a very deep 

 black color, and show no structure whatever. Parts of 

 certain other nuclei stain densely, while the rest retains its 

 original identity. Some of the nuclei have 4 to 6 nucleoli. 

 In Anolis two other kinds of nuclei appear. A few flattened 



Fig. 16. Diagram showing Compara- , . . , . . , ,, • iji r A l 1 



live Measurements of Retina in Eyes horizontal nuclei can be seen near the middle ot the layer 



of Anolis and Ampliisbana. . . , . i ,- i i ■ i 



and in the inner stratum are a number of large spherical 

 nuclei. Penetrating this layer are many fibers of Muller. Each fiber as it passes 

 through is characterized by a nucleated enlargement. 



The Inner Reticular Layer. — The inner reticular layer measures 20 /a in thick- 

 ness as against 45 /a in Anolis (8, figs. 15 a and 15 b). The method of staining 

 brought out no definite structures. The fibers of Muller pass through it as fine 

 vertical filaments. Occasionally there is a nucleus from the nuclear layer or from 

 the ganglionic layer which lies embedded in the edge of this layer. 



10 



