THE RETINA OF LUCIFUGA. 217 



unlike white corpuscles that have been abundantly fed with pigment granules. 

 Whether they carried these in with them or whether the remnant of the lens had 

 undergone a pigment degeneration, I am not able to say. 



The eye of the other side is much damaged in sectioning, but is essentially the 

 same. 



In a young 24 mm. long, evidently just born, the lens capsule of both eyes is a 

 large balloon, little wrinkled, and containing but little stainable material, all of it 

 of the same nature as that described above. 



In a young 27 mm. there is no remnant of a lens in the left eye, while in the 

 right there is the filmiest suggestion of the lens capsule, but nothing more. 



In an individual 28 mm. long the lens of the right eye is represented by a nearly 

 empty capsule, that of the left is shriveled, contains pigment, and is entirely in the 

 vitreous space, the pupil having closed. 



In an individual 38 mm. long the left lens is represented by a large empty col- 

 lapsed capsule, that of the right being small and collapsed. 



The lens capsule is the last part of the lens to disappear. In specimens over 

 40 mm. long, it was observed in only two doubtful cases ; in all others there was no 

 trace of it left. 



It is quite evident from the structure of the lens displayed in the unborn young 

 18 mm. long that it had passed its point of highest organization and was obviously 

 far along on the route of degeneration. Indeed the lenses of the young (12 mm.) 

 show no signs of fiber formation and also show indications that they have begun to 

 degenerate. 



Conspicuous and remarkable are the fibrous lens capsule which persists after its 

 contents have disappeared, the irregularity of the contained cells in their highest 

 development and their irregular distribution, and finally the pigment-fed phagocytes 

 in the capsule. 



THE RETINA. 



On account of the fluctuation in the size of the eye it is difficult to determine 

 whether the end of its development is reached with a length of 12 mm. or not until 

 a length of 20 mm. In the 4 embryos, 76 a, b, c, and d, about 20 mm. long, the eyes 

 fluctuate from a maximum 425 p. in longitudinal diameter in the longest, to 260 p. 

 in the shortest. If the embryo with the smaller eye had been of smaller size, it 

 would have been but natural to come to the erroneous conclusion that the eye 

 increases with age till the fish reaches a length of 20 mm. The same is true in 

 respect to the differentiation of the retina. One can not say in general that the 

 retina progresses in any respect between the length of 12 mm. and 20 mm. I can 

 only say that the most highly developed retina was found in an unborn individual 

 20 mm. long (plate 18, fig. A, and plate 24, fig. E). 



In the retina of the youngest individuals (12 mm.) there is a distinct differentia- 

 tion into a ganglionic layer occupying 0.24 of the total thickness, an inner fibrous 

 layer of the same thickness, a nucleolar layer 0.32 of the total, and a pigment layer 

 occupying 0.20 of the entire retina. The boundaries of the different layers are not 

 equally regular at all places, and the nuclear or ganglionic layer sends a connect- 

 ing series of nuclei in an irregular manner through the reticular layer in different 

 places. The pigment layer is well pigmented. The inner cell layer of the uvea is 



