MUSFX'M OF COMrAllATIVE ZOOLOGY. 61 



indication of ossification of the scleral cartilage, as is common in bony 

 fishes, has been seen. No trace of an argentea is to be found. All the 

 pigment is of the same dark brown granular variety, and, when seen 

 by reflected light, never gives the white, silvery color that is character- 

 istic of the crystalline material of the argentea. 



The choroid is exceedingly rudimentary, and in many specimens I 

 have been unable to detect its presence at all. In the eye frum which 

 Figure 13 was drawn (Fig. 13, chr.), — a specimen the eyes of which, as 

 will be seen furtlier on, are better developed in several respects than is 

 usual in these eyes, — it is more distinctly seen than in any other case 

 that I have studied. Here the layer of pigment is very thin ; it is in- 

 terrupted at short intervals, and cannot be traced for more than one 

 third of the distance through which it would normally extend. Whether 

 this pigment should be regarded as representing the lamina supracho- 

 roidea, or as belonging to the choroid proper, it is impossible to say. 



In a few instances (Figs. 13, 14, 15, chr.cpL), a layer of cellular tissue 

 has been found at the proximal pole of the eye, extending for a variable 

 distance toward the anterior rim of the optic cup, but rarely reaching it. 

 This layer is always closely applied to the outer surface of the pigmented 

 layer of the retina, and in some sections it seems to be continuous with 

 the pigment of the choroid. In some places (Fig. 15, ch7-. cpl.) the tissue 

 has very much the nature of formed connective tissue, while in other 

 places (Figs. 13 and 14, chr. cpl.) the cells are spherical or elliptical, with 

 indications at times of blunt processes, and with distinct nuclei. Where 

 cells of this kind occur, the layer is somewhat thicker than where the 

 structure is more characteristically that of connective tissue ; and in 

 several instances blood corpuscles (Fig. 13, cp. sng.) are found scattered 

 here and there in these thicker portions of the layer, indicating the 

 presence of capillaries. I identify this layer as the chorio-capillaris. 



A conspicuous structure in all the specimens studied is a thick, 

 usually short, somewhat lenticular mass of pigment occupying a position 

 usually at the proximal pole of the eye, at or near the entrance of the 

 optic nerve, by which it is pierced in some cases (Figs. 14, 15, etc., 

 gl. chr.). This mass is concentric with the surface of the retina, but is 

 always separated from it by a short though somewhat variable interval. 

 In some places the cellular layer just described in part occupies this 

 space, and in some places the thin layer of choroid pigment is seen to 

 enter the same space. The mass always lies within the sclerotic, and 

 is always composed entirely of pigment. I have been unable to find 

 any cellular or other protoplasmic elements in it. This body I interpret 



