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BLIND VERTEBRATES AND THELR EYES. 



the outer nucleated layer on the dorsal and proximal parts of the eye, but since in 

 all of the cases under consideration a good share of this space is attributable to 

 reagents, a more detailed description is useless. However, in these regions delicate 

 protoplasmic processes extend inward to the nucleated layer. The nuclei of the 

 pigmented layer stain much more faintly than those of the rest of the retina with 

 Biondi-Ehrlich, but just as deeply as the others with ha?malum. The cells of the 

 pigment layer are in one series, but occasionally a cell is found below the level 

 of the rest. A few cells very elongate in section may be mentioned here. They 

 were found (fig. 41 a) on the inner face of the pigment layer. These are important 

 in the interpretation of the structure of the eye of Troglkhthys roses, where they 

 are also found. Their origin and significance are not known. 1 



Fig. 41. (a) Sagittal Section through Right Eye of Typhlichthys sublerraneus, 25 mm. long. 



(b) Mullerian Nuclei (?) from Retina of Individual 25 mm. long. 



(c) Horizontal Section of Eye of Individual 40 mm. long. 



Rods and Cones with their Nuclei. — While the outer nuclear layer is very well 

 developed indeed, the rods and cones are not definite. In the most highly 

 developed eye there is a distinct outer limiting membrane. Without this are filmy 

 processes continuous with those from the pigment cells. Very rarely one sees an 

 elliptical, slightly granular body which may or may not be a cone body. The 

 outer nuclear layer is in some cases quite distinct, consisting of a compact series 

 of outer (cone?) nuclei, irregularly elliptical in outline, below which are a few 

 cells of a second series (rod nuclei ?) sometimes with their longer axes parallel with 

 those of the outer layer, sometimes horizontally disposed. 



1 See also Rhineura. 



