The Bryan daily eagle. (Bryan, Tex.) 1895-1898, 1897-08-20

Many Creatures Enabled 70 see by m,
Ald Of Sanaitive eht..

EYES NOT ESSENTIAL TO SIGHT
Many Creatures Enabled to see bv ,hs
Ala Of Sensitive shius.
From the Boston Journal: Eyes are
popularity considered to be quite nee
esaary 70 sight. but this ia an error.
II We are to believe DR.. Nagel. a re-
cent German experimenter. Many
Creatures without eyes can see: AT least
they can distinguish perfectly well be-
tween light and darkness and even be-
tween different degrees OF light. Thls
u the lowest degree OF seeing. to be
sure. but still II Ia really sight. and
diners scarcely more from the vision
OF some Insects that possess eyes than
THIS does from our own clear sight.
Creatures that see without eyes see BY
means Of their skins. All skins. says
Dr Nagel. are potential eyes: that Is.
they are sensitive to light In animals
that have eyes the constituencies has
beon highly localized and greatly in
creased-so that man. for instance.
has retina very sentative 10 light
and an expanse OF ordinary skin which
possesses a constituencies TO light 80
slight that II Is hardly conscious OF Il.
Yet his skin Is sensitive In some de-
gree. as Is proved by the fact that Il
sunburns-that Il. light may cause a
disturbance IN the pigment OF the skin
Just as Il does In that OF the eye. In
the eye the disturbance Is accompan-
led by a nervous change which sends
a lelegraphlc message along the optic
nerve 70 the brain In the skin. too.
there are nerves. and there are mes
sages also. but their tldlngs imprint
no image on the mind: they simply
express dlscomfort-cry out "sunhurn."
But IN many eyeless creatures the lack
OF eyes Il In part made up by increased
senslilyoness Of the whole skin sur
fsce 20 light Darwin long ago noticed
that earthworms. although they have
no eyes. will suddenly withdraw into
their holes AZ the approach OF a lighted
candle Some creatures seem most
sensitive 10 sudden increase Of light:
others 10 sudden dlmlnutlon. II a num-
Der OF oysters. kept In a vessel togeth-
er. are found 10 b open. they will
shut all At once II a dark object comes
between them and the light. Another
blyaiye. called PsammOdla. has long.
whltish. transparent tubes which pro-
trude from the sand IN which Il lies
buried. II these are suddenly lllumi-
mated they contract. and the brighter
the light the greater the contraction.
n a number Of them be carried into d.
rect sunlight they hasten 10 bury them
selves IN the sand. or. II there Is no
sand. they move restlessly TO and fro
In the water until they are exhausted.
In general. DR.. Nagel finds that crea-
lures which respond TO sudden shad-
ows are those that live In strong shells.
while those affected by a sudden in
crease Of light live In sand or mud.
from which they emerge occasionally.
In both cases the constituencies OF the
skin 20 changes OF light serves 10 pro-
tect the animal. How does the skin
acquire this peculiar sensltivenessf Il
will be best for the non-expert TO sus-
pend Judgment. since even the scien-
fists do not agree on this point. Il
may BE- that Il IL a universal and ru-
dlmentary property OF al skin. and
that animals with eyes have lost Il 10
a greater or less degree. because they
have no further need for Il. That Ia
one view Or Il may be that this prop
erty has been developed In eyeless
creatures Just because they are eyeless
and need Il. That IL another view.
Those who favor the latter opinion
point TO the fact that some OF the
creatures which now have skins SEN
sitive to the light are probably de-
scendants OF creatures with skins not
20 sensitive; In these instances the
sensitiveness must have been recently
developed Snaiis are sensitive. but
their relatives. the slugs. are not: this
looks a. n the former had acquired the
faculty. However this may be. Dr.
Nagle's study OF these curious and out
of-the-way facts Ia certainly interest
Ing and may lead In the future 20 an
advance In our knowledge OF the me-
chanism OF sight.