106 PATTEN. [Vot. II. 
away from the median plane of the eye, the cavity of the optic 
vesicle disappears (Figs. 67-70), the layer of rods becomes 
flattened out, and all the retinal cells and rods assume an up- 
right position, except those of the median ridge. 
THE RETINOPHORH.—I have shown that in Molluscs, the 
essential elements of the retina were colorless cells, bearing 
double rods, and containing two nuclei and an axial nerve 
fibre. These cells, or retinophorz, I maintained were formed 
by the fusion of two rod-bearing cells, in one of which the 
nucleus degenerates. The nerve fibres between the two cells 
come to lie in the centre of the double one, to form its axial 
nerve. Each cell retains its own rod, hence the double rods 
of the retinophore. Resting on these facts, and upon the 
supposition that the primitive nerve fibres were intercellular, 
I maintained that when sensory cells were found with axial 
nerves and traces of two nuclei, they should be classed as 
retinophorz, and must have arisen in the manner described 
above. In the Arthropods, I found the crystalline-cone cells 
had characteristics which led me to consider them as modified 
retinophore. My supposition was based on the expectation 
of finding in the ocelli of Arthropods, retinal cells, either very 
similar to the retinophorze of Molluscs or intermediate between 
them and the crystalline-cone cells. A comparison of the text, 
and the diagrammatic figures in Plate 32 of “Eyes of Mol- 
luscs and Arthropods,” will show that I expected to find the 
intermediate forms of retinophorz in the posterior eyes of 
Spiders, and in the eyes of Scorpions and Limulus, while the 
Molluscan type might be looked for in the ocelli of Insects and 
Myriapods, and in the anterior eyes of Spiders. 
The retinophorze now to be described, show that these ex- 
pectations have been realized, at least, as far as the ocelli 
of larval Insects are concerned. 
The first stages in the formation of the retinophore are found 
during the open-cup period of the eye. In Figs. 63 and 64, we 
see that the inner wall of the optic cup is closely packed with 
five or six rows of deeply stained nuclei; all of which are alike 
except the median one already described, and those belonging 
to a few large ganglionic ones, to be described later. In the 
next stage (Fig. 65), they appear to be greatly reduced in num- 
bers. This change is due to the fact that the cells are uniting 
