Staunton spectator. [volume] (Staunton, Va.) 1849-1896, 1896-07-29
EYELESS ANIMALS.
EFFECT OF CONTINUOUS DARKNESS
ON THE OPTIC ORGANS.

declares that animals which are placed
in new surroundings not fatal to life
undergo certain changes and modifica-
tions in their anatomical and physio-
| logical structures to meet the exigencies
demanded by such modification OF
surroundings. Thus, the founder and
his congeners, the turbot, the plaice,
the sole, etc., were, centuries and CEN
turies ago, two sided fishes, swimming
upright, after the manner Of the perch,
the bass and the salmon, with eyes ar
ranged one on each side Of the head.
From upright fishes. swimming proba-
bly, close to the surface Of the sea, they
became dwellers on its bottom, and in
order to hide themselves more efcetual-
ly from their enemies or their prey
they acquired the habit of swimming
with one side next to the ground and
Of partially or wholly burying them
selves in the mud, always, however,
with one side down. They thus became
fiat fishes, losing the coloring Of their
under surfaces, and their eyes migrating
across their foreheads and taking up
positions on the upper surfaces of their
heads.
Again, when animals are placed
among surroundings in which there is
no need for some special organ, this
organ degenerates and passes wholly or
partially into rudimentary condition
or entirely out of existence. These lat
ter effects of changed conditions on ami
mails are especially noticeable in the eff
feet of continuous darkness ON the Or
gans of sight of those creatures which,
owing to said mutilatiens, have been
compelled to dwell in darkness for un-
told ages.
The mole, far back i'll the past, had
eyes and gained its livelihood above
ground in the broad light Of day. But
owing to some change in its surround
ings it was forced to burrow beneath
the surface of the earth. Consequently
its organs Of sight have degenerated
and are now practically worthless SO far
as vision is concerned. All moles, how
ever, can tell darkness from light, con-
sequently are not totally blind-a GER
tain amount Of sight yet remains. This
is due to the fact that, although the op-
tic or sight serve, on examination, is
invariably found to be atrophied Or
wasted. there yet remain in the shriv
eled nerve cord true nerve cells. These
nerve cells transmit light impression to
the brain. Even if the optic nerves,
and, in fact, all Of the structures Of the
eyes, were absent I yet believe that the
mole could differentiate between day
light and darkness. The sensitive nerve
tufts and filaments Of the skin undoubt-
edly in certain instances respond to the
stimulation Of light, SO that totally
blind animals, animals with no rudi-
mentary organs Of vision whatsoever
and the inception Of whose ancestors
probably took place thousands Of years
ago, show by their actions that light is
exceedingly unpleasant to them. Thus
I have seen aetinophryas, minute, mi
croscopic animalcules, taken from the
river Styx in Mammoth cave, which
is their habitat, seeking to hide them
selves behind a grain Of sand that hap
pened to be drawn up in the pipette and
dropped upon the glass slide beneath
the object glass Of my microscope.
have repeatedly seen the blind fish
Of Mammoth cave seeking out the dark
est spots in aquaria. In point Of fact. l
think that it can be demonstrated that
light is directly fatal to these fishes.
They soon die when taken from the
river and placed in aquaria which are
supplied with an abundance of light.
These fish, although they have rudi-
mentary eyes, never have the slightest
remaining trace Of nerve cells in the
wasted optic nerve-that is. / have been
unable to discover any-thus showing
that their appreciation Of light is not
derived through the agency of their
eyes. An eyeless spider taken from the
same cavern showed like distaste for
light, and yet in this insect there is alb
solutely no vestige of an eye or its
nerves.
Finally, friend of mine, youth of
18, totally blind since birth, can differ
entiate between daylight and darkness.
On one occasion | carefully blindfolded
him and led him into the well lighted
office of brewery-he had never been
in brewery before-and asked him if
it were light or dark? He answered that
it was almost as light as day. / then
conducted him into the dark beer vaults,
and as soon as he passed the door he ex-
claimed: elbow cold and dark it is in
here!" Thinking that he might possibly
associate darkness with coldness, asked
him if this were the case. "No," he re-
piled, 81 see the darkness and feel the
cold. They are not the same. "
In these animals-and include man
continuous darkness has modified
sensibility (sense Of touch) to such an
extent that it has partially taken on the
functions of the useless organs-the
eyes; these creatures see with their
skins.
/ do not believe that there is crea-
ture in existence today, whether it has
eyes or not, which cannot tell the differ
ence between night and day.-Popular
Science News.