The Dawn of Reason | Page 9

for immediate
use.
Actual experimentation has taught that these animals can descry a man
at the distance of twenty or twenty-five feet. When approaching a
crayfish "town" for the purpose of making observations, I use the
utmost caution; otherwise, each inhabitant will retreat into its burrow
before I can come close enough to observe them, even with my
field-glasses.
The gyrinus, or "whirligig beetle," whose dwelling-place during the
greater portion of its life is, like that of the crayfish, in ponds and
streams, has remarkably acute vision. This insect is a true cosmopolite,
however, and is as much at home on dry land as it is in the water. All
seasons seem to be alike to it, just so the sun shines; for, during the
hottest days of summer and the coldest days of winter (that is, if there
is sunlight and no ice on the water), it may be seen on the surface of
ponds and streams, gyrating hither and thither in a seemingly mad and
purposeless manner.

Several of these creatures will be seen at one moment floating on the
water, still and motionless; the next moment they will be darting here
and there over the surface of the water, their black and burnished backs
shining in the sunlight like brilliant gems. Suddenly, it is "heels up and
heads down," and they disappear beneath the surface, each of them
carrying a bubble of air caught beneath the wing-tips; or, as the late
William Hamilton Gibson expresses it, "they carry a brilliant lantern
that goes gleaming like a silver streak down into the depths, for a
bubble of air is caught beneath their black wing-covers, and a diamond
of pure sunlight accompanies their course down among the weeds until
they once more ascend to the surface."[14] This little beetle is well
provided with eyes, for it has a large pair beneath its head, with which
it sees all that is going on in the water below, and another pair on the
sides of its head, with which it keeps a bright lookout above. That it has
remarkably keen vision with the latter pair, any one who has tried to
steal upon them unawares can testify.[15]
[14] William Hamilton Gibson, Sharp Eyes, p. 307.
[15] I have a distinct purpose in introducing these and other queer-eyed
individuals while discussing the sense of sight. I wish to demonstrate
through one or more of them the correlation of morphology, physiology,
and psychology, as formulated in the first chapter of this work. This is
one of the most important facts in the doctrine of evolution, and upon it
is based the law of progressive psychical development from the simple
manifestations of conscious determination in the lowest organisms to
the most complex operations of the mind in man.
The queerest of all queer-eyed animals is, probably, the Periophthalmus,
a fish inhabiting the coasts of China, Japan, India, the Malayan
Archipelago, and East Africa.[16]
[16] Semper, Animal Life, p. 374 et seq.
I use the word coasts advisedly, for this strange creature when in
pursuit of its prey leaves the sea and comes out on the sands, thus
existing, for the greater portion of its life, in an element which,
according to the general nature of things, ought to be fatal to it. The

laws of evolution have, however, eminently prepared it for its peculiar
mode of life, for its gill-cavities have become so enlarged that when it
abandons the sea it carries in them a great quantity of water which
yields up the necessary supply of oxygen.
Its locomotion has been provided for likewise, for continued use along
certain lines has so developed its pectoral fins that the creature uses
them as legs, and jumps along at a surprising rate of speed.
Its eyes are very large and prominent, and possess, for a fish, the
peculiar faculty of looking around on all sides, hence its name,
"periophthalmus," which is derived from the Greek words, [Greek:
peri], around, and [Greek: ophthalmos], eye. These eyes are situated on
top of the animal's head, and present a very grotesque appearance.
The favorite food of this fish is Onchidium, a naked mollusk. And, in
the matter of eyes, this last-mentioned creature is itself worthy of
remark. Its cephalic, or head, eyes are like those of other mollusks of its
genus, and are not worthy of special mention, but its dorsal eyes,
sometimes several dozen in number, are truly remarkable. These eyes,
although they are very simple in structure, in type are the same as those
of vertebrates, having corneæ, lenses, retinæ, and "blind spots." (In the
vertebrate eye, the spot where the optic nerve pierces the external layer
of the retina is not sensitive to light impressions; hence, it is called the
"blind spot.")
When this mollusk sees periophthalmus bounding