228 NUNNELEY, ON THE RETINA. 
fish, and even here, they do not, so far as I can ascertain, 
exactly correspond with the description given by Hannover ; 
and in the turtle, where the bulb is distinct. In sections of 
retina from the higher animals, which have been dried and 
moistened by various reagents, or even fresh retina treated 
with dilute chromic or acetic acids, it is not difficult to find 
various-shaped particles, which may be supposed to be these 
bodies, but inasmuch as they are not to be detected, so far 
as I can ascertain, in the perfectly fresh eye where its retina 
alone is examined, I am doubtful of their actual existence 
as distinct bodies. There is no difficulty whatever, when 
regarding the undisturbed external surface of the retina of 
either reptiles or mammalia, of recognising the forms figured 
by Hannover and Bowman, which they consider the cones 
or bulbs not in focus, but I have always failed in detecting 
the appearances represented by them im profile, and I am 
more inclined to think the bodies seen at a deeper level, and 
out of focus, when the outer ends of the rods are in focus, 
not as cones or bulbs, but as the outer portions of the 
granular layer to be presently described, and upon which the 
ends of the rods rest, indeed are closely attached to; or as 
the inner ends of the rods themselves, not in focus. 
That coffee-shaped granular bodies, often more or less 
bilobated, are to be seen in the retina of many animals is 
certain, but I have so commonly seen rods to assume this 
form while under the microscope, that I strongly suspect 
many of the forms which have been described as cones are 
really only modified rods. That bodies at all resembling 
the cones jumeaux of fish, which may be regarded as the 
type of these cones, exist in mammalia or most reptiles, I 
am persuaded is incorrect. I have examined the eyes of the 
alligator, the chameleon, the newt, the frog, and toad, the 
last three over and over again, both young and old, fresh and 
dried eyes, without being able to detect any. Moreover, 
Hannover’s own account of what he calls these bodies in 
birds shows them to be altogether different structures from 
what he describes under the same name in fish. In birds 
there are, as has already been stated, numerous conoidal 
bodies surmounted by a brilliant coloured globule, but they 
appear to differ very little from rods, and their broader end 
is external, while they are in no respect double, nor have 
they any sharp conical points, either single or double.* 
* To describe bodies which differ so esscntially as the cones jumeaur of 
fish, and the elongated bodies which are surmounted by a coloured globule 
in birds, as the same structures, appears rather as a predetermination to 
find an uniformity of structures, than a simple representation of what 
