SCHULTZE, ON THE RETINA. 25 
ponderate greatly over the “rods.” ‘The same disposition is 
found in the retina of reptiles. In the turtle the arrange- 
ment is precisely the same as in birds, whilst in the lizards 
the “ rods” are wholly wanting, as they would appear to be 
also in snakes. An exception, however, to this rule, as re- 
gards birds, is afforded in the owl, in several species of 
which (S. aluco, noctua, and flammea) the preponderance in 
number would seem to be in favour of the “ rods;” and from 
this circumstance, as well as owing to the enormous length 
of the “rods”? in proportion to the “cones,” the mosaic 
aspect of the outer surface of the retina in these birds bears 
a striking resemblance to that of the bat. And owing to the 
same condition also, the owl’s retina is almost everywhere 
destitute of the colours so characteristic of the membrane in 
other birds. And another remarkable circumstance with 
respect to the retina in owls is the total absence in it of red 
pigment-globules; and even the few yellow cones become 
paler and paler towards the ora serrata, until at length they 
are entirely colourless. These facts would seem to point out 
that, as the retina of nocturnal mammalia is distinguished by 
the total absence of ‘‘ cones,”’ so in the case of the owl the 
_ comparative paucity of the same elements, together with the 
pale colour of the few pigment-globules, may also be con- 
nected with its nocturnal habits and avoidance of light. It 
would, therefore, M. Schultze remarks, be very interesting 
to examine the retina of other nocturnal birds, as of the 
Caprimulgide, &c. 
Another and most characteristic peculiarity of the retina 
of birds, some reptiles and amphibia, but more especially of 
the first, is the presence in most of the “cones” of a spherical 
globule of red or yellow colour, but chiefly yellow, and which 
is situated at the junction of the inner and outer segments, 
that is to say, at the internal end of the latter, whose whole 
diameter is occupied by it, and consequently all the light 
reaching the outer segment of the cone must pass through 
this coloured medium. The author’s observations would 
seem to show that the yellow colour predominates in the 
more sensitive parts of the retina. At least, this presump- 
tion arises from the circumstance that in such birds as the 
pigeon, crow, and hawk (although swift-flying birds), which 
present a fovea centralis (in the hawk two), the elements in 
that part all contain yellow spherules. 
The retina of reptiles closely resembles that of birds. In 
lizards, according to Leydig, two kinds of elements are dis- 
tinguishable—one of a slender form, and furnished with a 
deep yellow spherule; and others of a broader conical shape, 
