140 



BLIND VERTEBRATES AND THEIR EYES. 



geneous, vesicular, ellipsoidal nucleus situated near the outer end of the cell. This 

 nucleus is strikingly different in shape and constitution from the same structure in 

 Chologaster. It stains but faintly and then homogeneously. Just within the 

 nucleus there is a well-defined mass of dense pigment forming a cap over the inner 

 side of the nucleus and at times encroaching on the rotundity of its inner outline. 

 This pigment mass evidently has its counterpart in Chologaster where a solid band 

 of pigment is found just within the nucleus. In depigmented cells this pigment cap 

 is seen as a deeper-staining, more dense protoplasm than the rest of the cell. From 

 this pigment segment a prolongation, much poorer in pigment and containing a 

 central uniformly staining core, extends toward the interior of the eye. This core, 

 which in reality extends also into the pigmented section, occupies the position of 

 the cones in Chologaster. In no case have I been able to trace any connection 

 between these bodies and the outer nuclear layer. They are sometimes in several 

 esgments or in a number of spherical bodies, and occasionally two are seen side by 

 side in the same cell in tangential section. In position they certainly suggest cones, 



i-hr 



FIG. 52. Section near Posterior Face of Left Eye of Small Individual, showing particularly Position 

 of one of Scleral Cartilages behind Eye and Thick Choroid filled with more or less Angular Mass 

 ot ( Ir.inular Pigment. This Eye shows one of the Largest Accumulations of Pigment noticed. 



and this suggestion is heightened by the presence in the inner end of some of the 

 cells of a vesicular structure very similar to the nucleus, but frequently with an 

 ;i uvular indentation on the surface. These occupy the relative position of the cone 

 I K )i lies, they are by no means found in all eyes. The evidence seems to point most 

 strongly in favor of the supposition that they are cones. One of the cells measures 

 as follows: diameter of cell, 0.007 mm. ; nucleus, 0.007 by 0.007 mm. ; deeply pig- 

 mented mass, 0.007 mm. ; total length of cell, 0.036 mm. No rods have been found. 



In many individuals, and strikingly so in two specimens 25 mm. (fig. 53, am.) and 

 35 mm. long (fig. 54 b) respectively, deeply staining spherical bodies, much smaller 

 than the nucleus and staining much deeper, are present in the pigment cells. Those 

 stained with rui-malum are quite dark and give the appearance of a large centro- 

 some. These 1 take to be myeloid bodies noted in the pigment cells of the frog and 

 other forms. 



In most individuals the high development of the pigmented region, above 

 described, is not found. In some individuals the pigmented layer is composed of 

 Hat pavement cells, forming a large vesicle (plate 10, figs. D and G). In others the 



