142 



BLIND VERTEBRATES AND TEELR EYES. 



in many sections of Chologastcr and the method of the closing of the pupil in Typh- 

 lomolge is as I have suggested. 



The Nuclear Layers. — Within the pigment and cone layer lies a nuclear layer 

 made up of about four series of cells (3 to 7 in figs. 50, 54 e). The nuclei reach 

 from 2.5 to 3.5 jx in diameter. Rarely I have succeeded in staining the smaller nuclei 

 different from the larger. They are, in such cases, more refringent, the large nuclei 

 being granular. The larger nuclei may be the spongioblasts. In a young indi- 

 vidual this difference was well marked. Here the smaller cells were confined to 

 the proximal part of the eye (fig. 53). A separation of the nuclear layer into an 



.nl.l 



Fig. S4- From an Individual 35 mm. long killed in Perenyi's Fluid and stained with Mayer's Hsmalum. 



(a) Outer Nuclear Layer in Center, Choroidal infolding on Left. Lower Part of figure passes through Choroidal Fissure Area 



and Pigment Cells are here undifferentiated, quite different from those of the Dorsal Part of Same Section. 

 (6) Further Forward and shows Strands of Optic Nerve (». op.) and Elongated Nuclei of Inner Layer of Iris irregularly arranged 



(»/. /.). Choroid and Sclera can not be separated from each other except where Latter is differential as Cartilage, in front of Eye. 

 (c,d) Surface and Deeper Focus of Section passing through Iris and Central Ganglionic Cells. In fig. d Irideal Structure with 



Elongated Inner Nuclei is well shown. 

 (e) Passes near Center of Eye. Choroidal Fissure Epithelium seen below and Irregular Mass of Section through Elongated Irideal 



cells (nl. I.). 

 (/) Passes through Optic Nerve and Pupil of Same Eve as fig. e. 



Figs, a to d are from Left Eye, e and / from Right Eye. All under Lenses 2 mm. and 4. 



inner and outer with an intervening outer reticular layer I have noticed but once. 

 In this eye a slight separating space was found on one side, and here there were 

 one or two cells that may be fulcrum cells. If so, it is the only indication of this 

 layer in all the preparations made. The suppression, partial or total, of the sepa- 

 ration into an outer and inner layer, has also been noted by Ritter in Typhlogobius. 

 The Inner Reticular Layer. — This layer is always well developed ; occasionally 

 a few nuclei extend partially in from the outer nuclear layer. It is frequently thicker 

 on the dorsal half of the eye (fig. 54/) than on the ventral half, but sometimes the 

 reverse. In figure 50 the ventral half is but 0.012 mm. Nuclei have but once been 



