us 



BLIND VERTEBRATES AND THEIR EYES. 



The outer reticular layer is well developed. Its boundary is irregular on 

 the side of the inner nuclear layer, but more regular on the side of the outer 

 nuclear layer. 



Horizontal cells are very few and widely separated, if, indeed, this layer is repre- 

 sented at all. A few cells horizontally placed are present on the inner face of the 

 outer reticular layer (fig. 39 a). 



The inner nuclear layer is represented in the smaller specimen by two series 

 of small rounded nuclei (fig. 39 a, 5-7). In the larger specimen a single irregular 

 series represents this layer (figs. 40 b, c, 5-7). Besides the rounded nuclei there are 

 a few irregular-shaped ones and other elongated ones. Some of the latter lie in 

 the plane of this layer, others at right angles to it. The latter are probably Mul- 

 lerian nuclei. 



O 



FIG. 39. Cliohgaster cornvtus from a Specimen 27 mm. long. 



(a) Entrance to Optic Nerve and Part of Retina, 2 mm. and 6. 



(6) Oblique Section through Pigment Layer to near Outer Nuclear Layer, 2 mm. and 4. 



(c) Bases of Cones and Underlying Nuclei of Outer Layer. Nuclei, in black, are in deeper focus, 2 mm. and 8. 



(d) Nuclei of Outer Nuclear Layer and Deeper-lying Nuclei of Inner Nuclear Layer, 2 mm. and 8. 



The inner reticular layer is well developed and contains a few round nuclei, as 

 in pH/iillifcrn.s. In addition, it contains some vertically elongated nuclei at times 

 reaching through half the thickness of the layer. These are also evidently Miil- 

 lerian nuclei. Some of them extend from the ganglionic layer outward, others 

 from the inner nuclear layer inward (fig. 40 b). 



The ganglionic layer is very imperfect, being represented by scattered nuclei 

 embedded in the inner layer of the reticular layer. In this layer we have a decided 

 degeneration by a reduction of the number of elements (fig. 40 a, 9). 



A nerve-fiber layer is not evident in cross-section. 



The pigmented layer has not been decreased nor have the reticular layers 

 degenerated materially beyond Chologaster papilliferus. The nuclear layers, on 

 llu- other hand, have been very materially affected. The outer layer has been 

 much reduced. But this need not necessarily imply degeneration. The inner 



