THE EYES OF TYPHLICHTHYS. 



125 



indefinite nature as that of the eye itself, with which it is continuous. No pigment 

 accompanies the nerve as a distinct layer, but here and there, as in the covering of 

 the eye, a pigment cell may be seen, while about its entrance into the brain cavity 

 some pigment cells are also found. 



Epithelial Part of the Iris. — The pigment cells, as in Amblyopsis, decrease in 

 height toward the irideal portion of the retina, where they become a series of pave- 

 ment cells with rounded nuclei directly continuous with a layer of cells with elon- 

 gate elliptically nucleated cells forming the inner layer of the iris. The homologues 

 of the elliptically nucleated cells are found in the iris of Chologaster in the region 

 of the ora serrata. At the junction of the outer and inner layers of the iris the 

 cells are sometimes heaped up, making the irideal margin quite thick (fig. 43 b). 

 There is in some cases a distinct free pupil (fig. 43,) while frequently the opening 

 is directly continuous with the choroid fissure which may remain open in this 

 region (fig. 41 c). 



Fig. 43. (a) Iris of Eye shown in 42 a. 



(6) Section through Iris and Lens of Right Eye of Typhlichthys 42 mm. long. 

 (c) Median Vertical Section of Left Eye of Same Individual. 



Lens. — The lens was not found in all eyes ; when present it is situated at the 

 anterior end of the choroid fissure or behind the iris. It consists of but very few 

 cells. These cells are undifferentiated. No fibers or other signs of differentiation 

 are at all evident. The, lens cells are not distinguishable from the neighboring 

 cells, and only the faint lines seen to surround the group serve to distinguish 

 them. 



Vitreous Body and Hyaloid. — The choroid fissure is distinctly evident in speci- 

 mens at least 42 mm. long, not as a distinct fissure, except in front, but as a line 

 along which the various nucleated layers of the retina are merged. In the distal 

 part of the retina the fissure is not entirely closed, and it here leaves an opening 

 into the vitreous cavity which is more distinct and larger in the large specimens 

 than in the smaller ones (fig. 41 c). The vitreous cavity, when present at all, is 

 confined to a very narrow region just behind the lens. Here a few oval nuclei 

 and an abundant supply of blood-vessels are to be found (figs. 41 c, 43 a, b), 

 the latter communicating with the exterior through the open part of the choroid 

 fissure. The vitreal body or cavity does not extend far into the eye, and in the core 

 of ganglionic nuclei, where the vitreal cavity does not extend, the hyaloid mem- 



