The Washington times., 1920-12-26

Mainly Responsible for "Depth
Perception" and Not the Com
bined Use of Our Two Eyes, ~
Formerly Supposed.
X FANY scientists have been patiently
N studying the eyes of men and ami,
AVA mails, finding out how we see. what
kind Of things we see most quickly, how
our eyes are deceived, and other interest
Ing matters.
The results Of thousands of investiga-
tions into the eyes are summarized by
Professor Leonard Thompson Troland, of
Harvard University, IN the Psychological
Bulletin.
The animals have eyes adapted to their
various ways OF living. You have probably
noticed how the pupil of the cats eye
forms a narrow slit running UP and down
the eyeball. The investigators have found
that the pupil Of pussys eye has longer
vertical than horizontal axis. because the
cat is primarily climbing animal, and this
sort OF pupil favors the perception OF OBJ
jects seen looking up tree or down from
tree.
The partly closed pupil OF a Sleeps eye
Is exactly the opposite OF the cats eye. in
that It has a longer horizontal than vertical
axis, This is because the sheep needs, to
take IN the contours of the surrounding
landscape as far as possible. 1t Is not
climber, but usually stands on fiat places.
Being hunted rather than a hunter, 1t needs
the increased illumination at the sides OF
the eyes which is provided by the special
shape Of its pupil.
Studies have been made OF the wonder
full seeing powers Of the hawk and other
birds Of prey. These animals have points
of most acute vision in the eye, called
"foveae"' Observations on the buzzard
show that each eye functions separately
and that the "fovese" of each eye also act
Independently, much as do the fingers OF
tn hand. In the acute vision spot" there
are tiny colored oil droplets. The colors
are yellow, orange and red, and their func-
tons are probably to form protective
filter.
The retina OF the human eye has a
Sovea or spot OF most distinct vision, but
the fovea OF the birds is finer and more
complicated than that OF man.
It Il interesting to learn that wasps and
some other insects have good color vision
and are attracted by color and color con-
trasts. Bright light stimulates the honey
bee to active movement, and especially the
worker bee. When one eye OF bee is
DbCkeutu Inc IhSStJ hoNcp III u IVY ~"
the direction Of the functioning eye.
The compound eye Of the butterfly and
other insects is sensitive to color and dis
dance. The butterfly distinguishes with
its compound eye objects at distance OF
an inch to three feet.
Just why the flies have compound eyes,
consisting OF hundreds of separate facets
has always been a puzzle, but the latest
experiments indicate that they are used to
soc very near objects.
Oysters and other molluscs, which do
not have distinct eyes but only Visual
cells, are sensitive to sudden changes OF
light. mussel was seen to respond to
light after 1.3 seconds.
Many of the lower Invertebrates have
various types OF visual cells, which sug-
Eest the line OF evolution TO the fully de-
yeloped vertebrate eye. The earth worm
has an eye, or visual cell, which barely
distinguishes light from darkness. The
llmpet has a visual cell which only per.
ceives motion and direction. The eye OF
the tube worm has only rudimentary
perception Of form. 80. U.s..
Aud-minnows and sticklebacks were