—~90 Trans. Acad. Sci. of St. Louis. 
tion lies. - | have sections of the larval eye in which the 
ganglionic layer seems to be composed of three more 
or less well defined rows of cells, and, on the other hand, 
sections of the adult eye in which six or seven rows of 
cells may be counted. | 
Outside of the ganglionic layer the inner plexiform 
(reticular) layer forms in all the sections, whether they 
are from the eyes of the larvae or of the adult, a com- 
‘paratively broad band. No details can be made out in 
my sections in this layer; it appears as a uniformly 
stained homogeneous tissue. Outside of this layer lies 
apparently a single very broad nuclear layer, where in 
the human retina we have the two nuclear layers, sep- 
arated by the external plexiform layer. This thick 
nuclear layer shows, sometimes very indistinctly, some- 
times more plainly, a separation between the large inner 
mass of nuclei and the two outermost layers, that is, what 
in the: human eye would correspond to the layer of rods 
and cones and their nuclei. From the foregoing it is 
seen that while in my specimens there is neither in the 
eyes of the larva nor in those of the adult a distinct outer 
plexiform layer, still there is a sign of some separation 
between the large inner and these two outermost nuclear 
layers. The outermost layer, corresponding to the rods 
and cones, consists of cells which are arranged pallisade- 
like and markedly differ in their shape and nature from 
the others. While in the larval eyes they often appear 
broader at the base and thinner at their outer end (see 
Fig. 14), in the adult eyes their shape is more rounded 
at the outer end. It is impossible to distinguish between 
rods and cones, the cells appearing all of the same ovoid 
shape. (See Figs. 15, 16, 17.) 
According to Kigenmann the so-called outer segments 
of the rods and cones are lost in the adult eye. While 
in most of my specimens the space between the rods and 
cones and the pigment epithelium is filled with a mass 
of detritus which contains numerous streaks and heaps 
of fuscin needles and which takes up a slight stain with 
