﻿214 BLIND VERTEBRATES AND THEIR EYES. 



In a specimen 94 mm. long the ophthalmic vein can readily be traced. In a 

 specimen 93 mm. the ophthalmic vein of the right eye is seen to measure 40 jx as 

 compared with a diameter of the eye of about 100 /u.. A few blood cells are seen in 

 this eye. A considerable mass of pigment is developed in the choroid, in places 

 15 /A thick. It is not possible to make out any vascular network either in the cho- 

 roid or in the eye. Very few blood-vessels are seen about the eye itself, although 

 the vessels leading to and from the eye are very large and filled with blood corpuscles. 



In the eyes of older individuals there is a great diminution in blood in and about 

 the eye. The capillary meshwork in the choroid and the vitreous vessels are no 

 longer readily distinguishable, their reduced size being further indicated by the 

 absence or inconspicuousnessof the large choroidal veins seen in 76 a. The ophthal- 

 mic vein is, however, very large and well filled with corpuscles in even the oldest 

 individuals. It has here the appearance of a sinus rather than a vessel. Certainly 

 the necessity of the eye does not require a vessel equal to nearly half of the total 

 diameter of the eye as in the case of 42. 



The entire vascular arrangement gives the impression of being abnormal. A 

 key to the large blood-vessels or sinuses is probably found in several of the eyes of 

 Stygicola to be described later. In them it was definitely determined that blood 

 lakes had formed in and about the eye that were entirely cut off from the circu- 

 lation. 



PIGMENT MASSES NEAR THE EYE AND THEIR SIGNIFICANCE. 



Near the eyes of all specimens above a certain size there are found masses of 

 pigment. They are probably cells gorged with pigment which are aggregated in 

 one or several masses. For instance, near the left eye of the largest fish examined, 

 there is a large (80 x 128 /x in section) pigment mass 144 /a from the eye. It is oval 

 in its proximal end ; truncate in its distal. Some of the denser fibers of the capsule 

 surrounding the eye extend out to it. Another less distinct pigment mass is found 

 in contact with the eye in a manner to make it difficult to determine its relation to 

 the eye. It may be part of the retinal pigment (plate 23, fig. b). On the right 

 side there are several pigment masses located in the orbital fat near the eye : one, 

 80 X 96 /A ; another circular mass, 32 fi ; another, 80 /it in diameter near the eye ; and 

 still another, 32 x 48 fi. Some of these are evidently composed of lobes or distinct 

 subsidiary masses. In very thin sections it can be seen that the cells comjoosing 

 the masses are filled to distention with granules about 0.7 ju, in diameter, just such 

 as are found in the pigment of the retina and in tlie subepithelial pigment of the 

 skin. The cells measure 9 to 14 /a in diameter. They are rounded, sometimes 

 flattened where they are in contact. When fully pigmented their well-defined 

 outlines and the occasional undoubted relation of nuclei to them are the only 

 indications that they are cells. 



Remote from the densely filled cells, a number of cells can be made out in one 

 individual in which the nucleus is located at one margin and the cyto])lasm con- 

 tains a few, or even but one, granule, while in others no granules are found. The 

 nucleus is always kidney-shaped with the concave side toward the cytoplasm. There 

 is, for instance, one nucleus near one of the large masses, similar to the nuclei in the 

 mass flattened on one side and associated on that side with a hyaline bag of definite 

 outline and containing a number of the pigment granules ; near it is another with 



