The Dawn of Reason | Page 6

frogs are kept in total darkness, the lower is the number of
color-cells and the smaller is the amount of coloring-matter. This
accounts for the fact that all animals which have dwelt in darkness for
untold ages are absolutely colorless. Pigmented or colored fishes,
nevertheless, having well-developed organs of vision, have been taken
from such depths (over a mile) as to preclude the possibility of a single
ray of daylight.[7] These fishes, however, are phosphorescent, and thus
furnish their own light. Moreover, I am inclined to believe that the vast
depths of the ocean, in certain localities, lie bathed in a continuous
phosphorescent glow, so that creatures living there neither lose their
color nor their eyes, sufficient light being present to prevent
degeneration. Where eyeless and colorless fishes are brought up from
great depths, there the ocean is not phosphorescent, but is in absolute
darkness.
[6] Semper, Animal Life, p. 83.
[7] Hickson, The Fauna of the Deep Sea, p. 150 et seq.
The preceding observations indicate that the sense of sight is a very old
sense, and that it is to be found in a primitive form (ocelli) in animals
of exceedingly low organization. That this is true, I will now attempt to
demonstrate.

Sight is the result of the conversion of one form of motion into
another--a conservation, as it were, of energy. Thus, waves of light
coming from a luminous body are arrested by the pigment-cells of the
retina in our eyes and are transmuted into another form of motion,
which is called nerve energy (in this instance, sight). It would seem that
as far as sight (vision is not included) is concerned, eyes of very simple
construction would amply satisfy the needs of thousands of creatures
whose existence does not depend upon vision. This supposition is
undoubtedly correct; there are many creatures in existence to-day with
eyes so exceedingly simple that they can form no visual picture of
objects--they are only able to discriminate between light and darkness.
Primitive eyes appear in animals very low in the scale of life; probably
the most remarkable of these early organs of sight are to be found in the
medusa, or jelly-fish. This creature, with its bell-shaped body and
pendent stem, bears a striking resemblance to an umbrella; noting this
resemblance, naturalists have given the name manubrium, "handle," to
the stem. Around the edge of the umbrella, and situated at regular
intervals, are certain round, cell-like organs, which vary considerably in
number. Some species have only eight, while others have sixty, eighty,
and even (in OEquorea) as high as six hundred.[8] These so-called
"marginal bodies" are the eyes of the jelly-fish. By many biologists
these organs are considered to be ears; they contain within their
capsules transparent bodies, which some scientists deem otoliths, or
"hearing-stones." Experimentation and microscopical examinations,
however, have taught me very recently to believe otherwise. In these
marginal bodies there is always a deposit of pigment; this is,
unquestionably, a primitive retina, while the transparent disk is,
indubitably, a primitive lens. That these creatures can tell the difference
between light and darkness is a fact easily demonstrated. Time and
again have I made them follow a bright light around the wall of the
aquarium in which they were confined. On one occasion I made some
medusæ tipsy, and their drunken gravity as they rolled and staggered
through the water in pursuit of the light was as sorrowful as it was
instructive; their actions in this respect were those of intoxicated men.
After I had siphoned off the alcoholized water and replaced it with pure,
they rapidly regained their normal status; whether or not any of them
felt any evil effects from their involuntary debauch, I am not prepared

to state.
[8] Lubbock, Senses, Instincts, and Intelligence of Animals, p. 84.
The eyes of sea-urchins are rather highly developed, having corneæ,
retinæ, and lenses. The lens generally lies in a mass of pigment, and, as
Lubbock remarks, looks like a brilliant egg in a scarlet nest.[9] The
eyes are scattered over the dorsal surface of the creature's body, and are
commonly situated just beneath the skin; they are, however, sometimes
elevated on pear-shaped bulbs. The eyes of starfish are generally quite
primitive in character, as far as I have been able to determine, being
simply pigmented spots which are supplied with nerves; in several
species, however, I have been able to make out lenses. The eyes are
arranged along the rays or arms, and vary in number.
[9] "In Solaster or Asteracanthion the lenses look like brilliant eggs,
each in its own scarlet nest."--LUBBOCK, Senses, Instincts, and
Intelligence of Animals, p. 132 et seq.
Even the stay-at-home and humble oyster has eyes (not the round,
fleshy muscle called the "eye" by gourmands and epicures, but bright
spots around the