﻿216 BLIND VERTEBRATES AND THEIR EYES. 



The appearance and gradual increase of these pigment cells and masses with 

 the beginning and progressive degeneration of the eye makes an intimate dejjend- 

 ence of the one phenomenon on the other very plausible. That pigment cells may 

 sometimes appear and become pigmented at some distance from the degenerating 

 eye is seen in the optic cavity of the largest individuals, where cells with but few pig- 

 ment granules were seen remote from the eye. Furthermore no phagocytes or 

 pigment cells in the process of gorging were seen in the eye. But in one case at 

 least there were found a number of fully pigmented cells between the pigment 

 layer and the rest of the retina. There seems to be little doubt, therefore, that 

 there is direct association of at least some pigmented cells with the degenerating 

 eye. Other indications as to the possible origin of the pigment masses are given 

 under the head of the lens. In some of the degenerating lenses cells containing 

 pigment granules were found. These cells are 6 ft to 9 /u in diameter. They are 

 most numerous in the lens of an individual 25 mm. long before accumulation 

 of pigment cells into masses has taken place. 



I have noticed similar pigment accumulations in the eye of Amhlyopsis. 



Pigment is found in very variable quantity and variously scattered in the con- 

 nective tissue surrounding the eye. The amount of this pigment seems to vary 

 inversely with the amount of pigment in the eye itself and to increase with age. 



THE LENS. 



The variation in the lens is not equaled even by the variation in the sclera. 

 Here, as in the sclera, we may begin the account with a description of the conditions 

 in the 4 unborn young taken from the ovary of a single mother. In 2 of these, 

 a and d, the lens is still present; in the other 2 there is no indication of it. In a and 

 d it consists of a sphere (plate 17, fig. b, plate 18, fig. a) incased in a fibrous mem- 

 brane of varying thickness, flocculent peripherally, becoming dense and firm and 

 containing nuclei proximally. The contents of this membrane are evidently under- 

 going histolysis. It is an amorphous, granular substance with partially dissolved 

 masses, some of them still showing nuclei. At other places the nuclei have degen- 

 erated into black chromatin lumps. There is absolutely no indication of lens 

 fibers. The cortical layer of the mass is at times compact over the distal surface 

 and this is the only indication of an epithelium covering this part. In the lens of 

 a stained with iron haemato.xylon, the center which chiefly contains the masses men- 

 tioned above is in part quite black. In b of these young the only indication of the 

 lens is a small vacuity in the connective tissue between the edges of the iris (plate 

 18, fig. b). There is nothing about this space e.xcept its position to indicate that 

 it was ever in the remotest way connected with a lens or its capsule. The lens 

 in still younger ones (12 mm.) is much as described in a and d. It consists of a 

 fibrous capsule filled with a mass of undifferentiated cells. 



In small individuals, ranging from birth with a length of about 24 mm. to 38 

 mm. in length, the lens is usually present in a more or less advanced degree of 

 degeneration. In the degeneration the solid contents of the lens capsule largely 

 disappears, the capsule collapsing or not. 



In a young 25 mm. long the lens capsule of the right is very much shriveled, like 

 a collapsed balloon and contains only about a dozen small cells, some of them 

 nucleated, others in part filled with dark brown pigment granules. These look not 



