MUSEUM OF COMPARATIVE ZOOLOGY. 65 
tinguished next to the inner reticular layer. These are slightly larger, 
on the average, than are the more superficially situated nuclei (st. n/. ex.), 
and they also stain somewhat more deeply. Usually each nucleus has 
a centrally placed nucleolus, and a not very distinct nuclear membrane. 
These nuclei undoubtedly represent the inner nuclear layer, though 
whether the entire layer or only its spongioblasts, it is impossible 
to say. 
Following this layer there is usually a single layer of nuclei (st. rl. ex.) 
that are considerably smaller and less distinct than those of the layer 
last described. Not only are the nuclei themselves here smaller and 
less distinct than those of the layers on either side of them, but spaces 
(st. rtl. ex.') are seen at intervals in which there are no nuclei at all. It 
seems quite certain that the outer reticular layer is represented by 
these spaces. 
Finally, outside of this layer follows another of nuclei about one or 
two deep (st. nl. ex.) that are again somewhat larger and more distinctly 
stained than those in the layer last described. No difference between 
them and those of the inner nuclear layer can be discovered, excepting, 
as said above, that they are slightly smaller, and stain a little less 
deeply. They are undoubtedly the nuclei of the rods, i. e. the outer 
nuclear layer, though I have been unable to trace a connection between 
them and the rods, and it is somewhat surprising that they are slightly 
greater in diameter than the rods. 
The external limiting membrane (mb. lim. ex.) is usually quite 
distinct. 
The rods are well— probably normally — developed, but I have 
searched in vain for cones. In the retina shown in Figure 18, they are 
quite variable both in length and diameter, being in a few instances 
knobbed at the outer ends (bac. cla.). It is, however, quite possible 
that both this appearance and the shortness of some of them are due 
to artificial causes, but the variation in diameter could scarcely be so 
explained. 
With a single exception, to be described more minutely hereafter, 
the Jens has been present in all the specimens studied in detail. 
It differs in no way in structure from the lens in normal fish eyes that 
I have examined ; i.e. it appears entirely homogeneous and structure- 
less after preservation in alcohol, Perenyi’s fluid, or picro-nitric acid. 
It is held in position very loosely, and consequently is easily displaced ; 
it is frequently found, in prepared specimens of the eye, pushed entirely . 
out of its proper situation into the somewhat yielding connective tissue 
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