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 fuscus 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 Kigenmann 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 
