NUNNELEY, ON THE RETINA. 231 
as belonging to two different bodies. There are a few cylin- 
drical rods, some of these are long and narrow, and appear to 
lie intermingled with the conoidal rods, while there are more 
which are shorter and thicker, and appear to be the inner 
ends of the altered conoidal rods broken off, and would thus 
resemble the conical portion of the cones jumeaux of fish— 
except that in fish the ends certainly are external, while in 
the turtle these portions as certainly he internally; and in 
fish the bulb breaks longitudinally into a coffee-berry shape, 
in the turtle it does not. There are few of the larger granular 
cells in the turtle as in fish; but the inner finely granular 
layer of cells is seen, as are the nerve fibres. (See Pl. X, 
where these bodies in the natural and altered condition are 
shown.) 
3. The granular, as it is called, forms the third layer of 
the retina. The name is not a very correct one, for these 
bodies are certainly not granules, as they have been described, 
but are cells filled with highly refractive, solid, granular nuclei. 
The walls are so thin and easily ruptured, that, after a time, or 
when reagents are applied, or insufficient power is employed, 
only granular matter is to be found; but when a perfectly fresh 
eye is examined with an eighth glass, or still better a twelfth 
and an achromatic condenser (see Pl. X,) not the least 
doubt can be felt as to their being cells filled with granules. 
They are usually irregular in outline, probably from com- 
pression against each other. They are found in all animals 
who possess a retina, but very far less in number in fish and 
reptiles than in man and mammalia, where they exist in 
enormous multitudes. They appear of pretty much the same 
size and character in most animals as seen on the slide by 
transmitted light. They are ofa pale yellow colour, and re- 
fract the light strongly like oil, their size varies considerably, 
some measuring z355, while many are not nearly half this 
size, some not more thanz5;55 of an inch. They bear a 
strong resemblance to, and are probably identical with, the 
cells found in the cineritious matter of the cerebral convolu- 
tions. They lie between the rods, which rest upon their 
outer surface, and the fibres of the optic nerve, and con- 
stitute in mammalia a considerable portion of the thickness 
of the retina, though not so much as the rods do. 
Bowman and Kolliker, both describe the granules as con- 
sisting of two layers, separated from each other by an indis- 
tinct fibrous layer, the outer of the layers being the thickest; 
but they are opposed to each other as to the size and shape 
of the globules forming them. Thus Bowman describes the 
granules forming the inner layer as smaller than the outer, 
