38 EIGENMANN AND DENNY. [VOL. II. 



number of these as compared with the much smaller cones 

 may be gathered from Fig. 2, a. 



In the larva 90 mm. long the outer segments of the rods are 

 much shorter and stain less conspicuously than in the younger. 

 The nuclei of the outer nuclear layer are distinctly in two 

 layers, whereas in the younger they are in three less regular 

 layers. The cones are correspondingly fainter than in the 

 young. It is surprising that whereas in the larva 90 mm. 

 long we find the rods and cones well developed they have 

 greatly degenerated or practically disappeared in the adult 

 only a few mm. longer. In an adult specimen 97 mm. long 

 the rods have retained their normal shape and position, but I 

 have not been able to detect any differentiation into inner and 

 outer segments. In longer ones most of the nuclei of the 

 outer series have become rounded at both ends. But one 

 cone was found in eyes of the adult over 100 mm. long. It 

 is shown in Fig. 6. In an adult specimen 103 mm. long 

 filmy rods are still evident. They appear as conical spaces 

 above the nuclei free from pigment rather than as possessing 

 any demonstrable structure. Just at the margin of the place 

 where the pigment has been torn from the retina one of these 

 is drawn out to a great length. The pigment in this individual 

 extends in places down between the cells of the cones. This 

 latter condition appears in a very exaggerated form in the 

 eye of Typhlomolge. In tangential section this condition 

 and the filmy rods give rise to the appearance represented in 

 Fig. 5, a. 



Distinct signs of ontogenic degeneration are also seen in 

 other parts of the retina. For instance, many nuclei of the 

 inner series of the outer nuclear layer are shriveled. In some 

 eyes the ganglionic nuclei have for the greater part lost their 

 granular structure and show a homogeneous pasty condition, 

 only a few cells with granular nuclei being present (Fig. 5). 

 The same is true in large part of the inner nuclei of the inner 

 nuclear layer. This condition of the ganglionic nuclei is not 

 entirely confined to the adult but is also found in the larva. 



Some of the modifications in the shapes of the outer nuclei 

 in the adult are shown in the figures. In Fig. 7 the upper 



