560 GEOKGINA SWEET. 



There is, liowever, nothing in Notoryctes to indicate that it 

 is any diifercnt from the rest of the pigment of the eye, i. e. 

 it is uveal in character. Apparently the edges of the pupil 

 have fused almost completely. Rliineura [4, p. 537], like 

 the more degenerate cases of Notoryctes, is oven more 

 reduced than these forms since there, even this rudiment of 

 the irideal epithelium has gone. The lens was but rarely 

 seen in Rhineura, while in Typhlomolge it has gone alto- 

 gether. In respect of the iris Scalops [8, pi. xviii, lig. 7, 

 and pi. xix, fig. 9] apparently resembles Rhineura, but in the 

 mole the lens is well marked, though only consisting of cells. 



Vitreous Humour, Hyaloid Membrane, Retina, and 

 Optic Nerve. 



With regard to these, there seem to be three stages in 

 reduction in Notoryctes. I, The first and most highly de- 

 veloped state found in this "mole" is that of which one sec- 

 tion is shown in figs. 1 and 4. In it the retina shows a division 

 into outer nuclear and outer molecular layers, and less defined 

 inner nuclear and inner molecular layers. The section drawn 

 shows fibres comiug from a group of cells at the anterior 

 end, evidently the remnant of the ganglion cell laj^er, and to 

 this extent is reminiscent of Amblyopsis [1, Taf. xiii, fig. o-I], 

 Typhlichthys [1, Taf. xiv, fig. 46], Troglichlhys [1, Taf. xiv, 

 figs. 54 and 56, and 6, Taf. viii, fig. 77], and Proteus [6, 

 Taf. V and vi, figs. 54, 55, 59]. In the next sections to that 

 shown in the figure the outer molecular layer is not visible, 

 the inner molecular layer being, on the other hand, more 

 sharply defined. In the sections vential to that drawn there 

 appears a longitudinal split (the vitreous cavity) separating 

 the fibres into two layers, and bounded by a thin membrane 

 with elongated nuclei, evidently the hyaloid membrane. 

 Anteriorly the split spreads in a Y-shaped manner, its an- 

 terior face being formed by the flattened cells of the uveal 

 layer of the iris, before described (cf. Typhlichthys [1, Taf. 

 xiv, fig. 42], Typhlomolge [2, plate iii, figs. 2, 6, 7], and 



