Alt — Histology of the Eye of Typhlotriton Spelaeus. 91 



eosin, there are sufficient places in which distinct pro- 

 cesses can be traced from the rods and cones toward the 

 pigment epithelium which take up eosin and are doubt- 

 lessly such outer segments. (See Figs. 14, 15, 16, 17.) 

 It seems, therefore, to me that, while no differentiation 

 can be made between rods and cones, the outermost layer 

 of the larval as well as the adult retina of Typhlotriton 

 represents what in the human eye are the rods and cones 

 with their outer segments. 



In order to find out whether epigaean relatives of 

 Typhlotriton have a very different arrangement of the 

 retina, I, also, studied the eyes of a specimen of Desmog- 

 nathus fuscns from Mobile, Alabama, kindly furnished 

 me by Mr. J. Hurter. The arrangement of the different 

 retinal layers in this salamander corresponds almost 

 exactly with that of Typhlotriton, especially the cells rep- 

 resenting the rods and cones are very much the same. 

 Except that where in Typhlotriton I found only an indis- 

 tinct separation of the outer two layers from the nuclear 

 layer, in Desmognathus I could with Mallory's stain here 

 and there demonstrate a blue line in this locality. It 

 seems, therefore, that the peculiar appearance of the 

 cells in the layer of rods and cones does not alone belong- 

 to Typhlotriton. The retinae of another salamander, 

 Diemyctilus viridescens, from Cliff Cave, Missouri, have 

 very different rods and cones, which are easily recognized 

 as such. 



A distinct nerve fibre layer, however, I have been just 

 as unable to find in the retina of Desmognathus and 

 Diemyctilus as in that of Typhlotriton. Either these 

 fibres have become disintegrated during the hardening 

 process, or, instead of forming a separate layer as in 

 man, they may, perhaps, run between the ganglionic cells 

 in such a manner as to be more or less hidden and not 

 easily distinguished. 



Like Eigenmann I have not found any network of blood- 

 vessels in the retina proper, yet in a number of sections 

 there is one large bloodvessel lying in the retina — but I 



