198 BULLETIN OF THE 
the eye, the evidence against the presence of a lentigen is apparently 
complete. 
The composition of the retina in the lateral eyes is much more diffi- 
cult to study than in the median eyes. This is due in part to the small 
size of the lateral retinas, and in part to their almost complete chitinous 
investment. To make isolation preparations is wellnigh impossible, by 
far the best results being obtained from the study of sections. 
Graber (’79, Pl. V. fig. 5), believing that the composition of the 
median and lateral retinas was essentially the same, has figured in the lat- 
eral eyes of Scorpio retinal elements with three nuclei. Moreover, the 
retinal elements are grouped, as in the the median eyes, in fives (Pl. V. 
fig. 8). 
Lankester and Bourne (’83, pp. 181-187) claim that the retina con- 
sists of unicellular elements, or nerve-end cells, as they call them, and of 
indifferent cells. The indifferent cells occur both between the nerve-end or 
retinal cells, as “‘interneural cells,” and around the edge of the retina, as 
“nerineural cells.” The indifferent cells all contain pigment; the retinal 
cells, in their opinion, are probably pigmented on their peripheries. 
In Centrurus the nuclei (Pl. III. fig. 18, ad. r. and nl. pe n.), as in 
the median retinas, are limited to the deeper portion and to the periphery 
of the eye, and Graber’s anterior and median nuclei are not present. The 
nuclei (nl. 7.) belonging to the deep portion of the retina are slightly 
larger than those (nl. pi n.) on the periphery, and very uniform in size. 
The fact that in this part of the retina there is only one form of nucleus 
leads to the conclusion that the retina in Centrurus is composed of only 
one kind of cells, and that here the interneural cells described by Lan- 
kester and Bourne do not exist. 
Sections perpendicular to the axis of this retina show immediately 
under the lens the sharp outlines of cells which deeper in the retina have 
their walls thickened into rhabdomeres. No additional cells, like those 
in the median eyes, appear in the outermost sections of the retina, and 
therefore the interneural cells, if present, must be limited to the deeper 
portion of the retina. The fact that there is no difference in the nuclei 
of this region leads me to believe that interneural cells are entirely 
wanting. In Centrurus the retinal cells (Pl. IIL fig. 19) show no 
tendency to be arranged in groups of five, and the rhabdomeric thicken- 
ing (rhb m.) takes place on all sides of the cell. This is particularly 
noticeable in examining the region nearest the lens. In the outermost 
sections the cells are sharply outlined and their walls are very thin. 
In the second or third section from the lens, the walls suddenly become 
