EYES OF CHOLOGASTER COENUTUS. 117 



than in papilliferus. Yet the per cent of the total thickness of the retina in pig- 

 ment is larger than in normal fishes. The nuclei of the pigmented epithelium are 

 irregular in outline. The part of the pigment layer about the nuclei forms a mass 

 of pigment in which cell boundaries can not always be made out. The pigment 

 about the nucleus is in granules; farther in, about the cone bodies, it is in prisms. 

 I have not been able to make out rods. The cones are irregularly elongate so that 

 the cone bodies are at various heights. The pattern of the twin cones has, there- 

 fore, not been made out. 



The outer nuclear layer consists of nuclei conical in shape, partly outside the 

 outer limiting membrane as in papilliferus, and a number of oval nuclei form- 

 ing a double series within these in the younger, a single series in the older 

 specimens. 



The outer reticular layer is distinct to the iris. Horizontal cells could not, with 

 certainty, be identified. Some of the cells lie without the inner nuclear layer in 

 the outer reticular layer and may be fulcrum cells. The inner nuclear layer is 

 three to four series of cells deep. Mullerian nuclei are present. If artificial 

 splitting should take place, the innermost series of nuclei separates from the outer 

 layers ; these probably correspond to the spongioblast cells of other retinas. The 

 inner reticular layer is well defined and contains very few cells. The ganglionic 

 layer consists of a single series of nuclei. A distinct optic fiber layer is not 

 present. 



The iris is much as in Chologaster papilliferus, much shorter in section than 

 in Chologaster cornutus. The inner cells of the retinal part are pigmented around 

 the margins of the pupil, while in papilliferus only the outer cells carry pigment. 



CHOLOGASTER CORNUTUS. 



The eye of Chologaster cornutus Agassiz is much larger than that of the other 

 species of the genus. The retina on the other hand is simpler. The details of 

 the measurements are given at the end of the account of this eye. But two 

 specimens were available for examination; they were preserved in alcohol and 

 respectively 27 and 43 mm. long. The very remarkable retina deserves much 

 fuller treatment than is possible with the limited material available. 



Leaving out of consideration the accessory structures of the eye as choroid, 

 sclera, muscles, etc., which are scarcely if at all different from the same structures 

 in papilliferus, the retinal characters may be briefly described. 



The pigment layer is very thick as compared with the rest of the retina, form- 

 ing over 60 per cent of the total thickness. The pigment cells form a sheath com- 

 mon to any pair of the twin cones. 



Connections between the cones and the outer nuclei could not be made out. 

 There are apparently fewer cones than nuclei. For the relation of the cones to 

 the underlying cells and of the latter to the nuclei of the inner, nuclear layer, see 

 figures 39 c and d. 



The outer nuclear layer consists of a series of nuclei closely packed together 

 with their longer axes vertical. Occasionally a fainter staining nucleus is 

 found among the bases of these cells with its longer axis horizontal (figs. 39 a 

 and 40 b). 



