90 Trans. Acad. Set. of St. Louis. 



tion lies. I 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 eve 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 Eigenmann 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 



