30 SCHULTZE, ON THE RETINA. 
from the centre of the macula in a meridional and forward direction, 
in order, after a longer ov shorter course, to reach the outer granular 
layer. 
of 4, In most mammalia the relative number of ‘ rods’ and ‘ cones’ 
is exactly the same as in man, with the exception, of course, of the 
macula lutea. But in many the cones are altogether absent. This is 
the case in animals which prefer darkness to light, such as the bat, 
hedgehog, mole, mouse, and probably a great many others. In the 
rabbit, which, as is well known, in the wild state inhabits subter- 
ranean passages, there are, it is true, indications of cones, though 
these appear to be in quite a rudimentary state.* The cat has dis- 
tinct though slender cones, which are placed wide apart, so that room 
is left between them for twice or thrice the number of ‘ rods’ than in 
the human retina. 
“5. Birds have many more ‘ cones’ than ‘ rods,’ the former, in fact, 
standing to the latter in the inverse proportion to that in which they 
occur in the human subject. In both the fovee centrales of the 
falcon ‘cones’ only exist [as well as in the single fovea centralis in 
some other birds]. But the owls almost resemble the bat, their 
retina containing but very few cones and an enormous proportionate 
number of rods. In their retina scattered ‘cones’ only occur at wide 
intervals, and these are so overcrowded by the very long outer 
segments of the ‘rods’ as to be seen with great difficulty. 
“6. The ‘cones’ in birds are distinguished by a very remarkable 
character. The greater number of them are furnished, at the end of 
the inner segment and immediately in front of the point of attach- 
ment of the outer segment, with a highly refractive globule, for the 
most part of a deep yellow or red colour, anything analogous to which, 
so far as is at present known, is wanting in all mammals. The yellow 
globules are more numerous than the red. The coloured globules 
have a diameter precisely corresponding with that of the base of the 
outer segment, so that no light can reach that part without passing 
through the globule. The few ‘cones’ which have no coloured globule 
contain at the corresponding point a strongly refractive colourless 
body, apparently of the same kind. The few ‘cones’ existing in the 
owl’s retina are furnished with pale yellow or colourless globules. 
Red globules are entirely wanting in the retina of those birds (Strix 
aluco, noctua, and flammea). 
“7. Among reptiles, in some, as the turtle, the retina appears to 
present the same structure as that of birds. Lizards and snakes have 
only cones, ‘ind in some instances these contain pigment-globules in 
the same situation as in birds (Lacerta, sp. Anguis fragilis), whilst 
others are without these coloured elements (chameleon and snakes). 
“8. The amphibia (frog, toad, triton, and salamander) have very 
thick rods and very minute cones, but in each of the latter is a bright 
yellow or colourless globule situated between the outer and inner 
segment. 
“9, The osseous fishes, so far as researches have hitherto gone, 
appear to possess rods and cones like the mammalia; and the latter 
are without coloured globules. Cartilaginous fish, on the other hand, 
as the ray and dog-fish, are wholly without ‘cones,’ like the bat 
among mammalia. 
“10. The difference which in mammals and fish is so apparent 
* It would be very interesting to examine the hare’s retina, which, though 
so closely allied to the rabbit, differs so much from it in its habits. 
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