ment. The habits of the animal 
determine the character of the eye. 
Birds of rapid flight and those which 
scan the earth minutely from lofty 
courses are able to adjust their vision 
quickly to long and short range. The 
eye of the Owl is subject to his will as 
he swings noiselessly down upon the 
Mouse in the grass. The nearer the 
object the more the eye is protruded 
and the deeper its form from front 
to rear. 
The human eye adjusts its power 
well for small objects within a few 
inches and readily reaches out for those 
several miles away. A curious feature 
is that we are able to adjust the eye 
for something at long range in less 
time than for something close at hand. 
If we are reading and someone calls 
our attention to an object on the 
distant hillside, the eye adjusts itself 
to the distance in less than a second, 
but when we return our vision to the 
printed page several seconds are 
consumed in the re-adjustment. 
The Condor of the Andes has great 
powers of sight. He wheels in beauti- 
ful curves high in the' air scrutinizing 
the ground most carefully and all the 
time apparently keeping track of all 
the other Condors within a range of 
several miles. No sooner does one of 
his kind descend to the earth than those 
near him shoot for the same spot hop- 
ing the find may be large enough for a 
dinner party. Others soaring at greater 
distances note their departure and fol- 
low in great numbers so that when the 
carcass discovered by one Condor 
proves to be a large one, hundreds of 
these huge birds congregate to enjoy 
the feast. The Condor's eyes have 
been well compared to opera glasses, 
their extension and contraction are 
so great. 
The Eagle soars towards the sun 
with fixed gaze and apparent fullness 
of enjoyment. This would ruin his 
sight were it not for the fact that he 
and all other birds are provided with 
an extra inner eyelid called the nicti- 
tating membrane which may be drawn 
at will over the eye to protect it from 
too strong a light. Cuvier made the 
discovery that the eye of the Eagle, 
which had up to his time been supposed 
of peculiarly great strength to enable 
it to feast upon the sun's rays, is closed 
during its great flights just as the eye 
of the barnyard fowl is occasionally 
rested by the use of this delicate semi- 
transparent membrane. Several of 
the mammals, among them befng the 
horse, are equipped with such an inner 
eyelid. 
One of my most striking experi- 
ences on the ocean was had when I 
pulled in my first Flounder and found 
both of his eyes on the same side of 
his head. All Flat-fish are similarly 
equipped. On the side which glides 
over the bottom of the sea, the Hali- 
but, Turbot, Plaice, and Sole are 
almost white, the upper side being 
dark enough to be scarcely distinguish- 
able from the ground. On the upper 
side are the two eyes, while the lower 
side is blind. 
When first born the fish swims up- 
right with a slight tendency to favor 
one side ; its eyes are on opposite sides 
of the head, as in most vertebrates 
and the head itself is regular. With 
age and experience in exploring the 
bottom on one side, the under eye 
refuses to remain away from the light 
and gradually turns upward, bringing 
with it the bones of the skull to such 
an extent that the adult Flatfish 
becomes the apparently deformed 
creature that appears in our markets 
as a regular product of the deep. 
The eyeless inhabitant of the 
streams in Mammoth Cave presents a 
curious instance of the total loss of a 
sense which remains unused. These 
little fishes are not only without sight 
but are also almost destitute of color 
and markings, the general appearance 
being much like that of a fish with 
the skin taken off for the frying pan. 
iiS 
