EYE OF NOTORTCTES TYPHLOPS. 561 



Proteus [6, Taf. vi, fig. 59]). In this eye there was no 

 choroid split nor pupil visible. The fibres from the " nerve- 

 fibre layer " collect posteriorly, and leave the eyeball as shown 

 in fig. 4; passing individually through the pigment and 

 sclero-choroid layer which is not broken here, and then back- 

 wards, becoming lost among the connective tissue fibres, 

 which form a sheath for them, continuous with the sclero- 

 choroid itself, which " tails off '^ here posteriorly. Un- 

 doubtedly these fibrils represent a degenerate optic nerve, 

 but it is impossible to actually prove their nervous character, 

 as I have no fresh material to work on. Indeed, they might 

 readily be accepted as fine connective tissue fibres with 

 elongate nuclei, lying lengthwise between the fibres, there 

 being no difference whatever in appearance, as indicated by 

 fig. 4. In one other section there was a distinct but narrow 

 cleft in the pigment wall near the same region, but nothing 

 could be found passing through. Nor in the material at 

 hand have I been able to detect any differentiation in the 

 cells of the retinal layers. One is led to believe that a thin 

 more or less definite layer of cells, exterior to the "nerve- 

 fibre" layer, represents the ganglion cells, but no difference 

 in structure can be seen from cells with slightly more deeply 

 staining nuclei, which are scattered all through the nuclear 

 layers. 



In the other two stages of degeneration the cavity of the 

 ball is occupied by a mass of cells, generally much crowded 

 together, without any trace of special arrangement. 



In Stage II (to which belongs the eye in which the indi- 

 cation of a pupil was seen, as described above) a choroid 

 fissure was present at the outer and ventral side, which 

 opened into a semicircular, very narrow slit-like cavity, 

 bounded posteriorly by a hyaloid membrane. It was almost 

 filled by connective tissue fibres, which have entered from 

 the sclero-choroid by the choroid split (cf. Myxine [6, Taf. 

 iv, fig. 40], Typhlichthys [1, Taf. xiv, fig. 49, and pp. 575-6], 

 and Rhineura [4, pi. xxxiv, fig. 4, and p. 538]. The anterior 

 boundary of this vitreous chamber, such as it is, is formed in 



