The Chickasha daily express. (Chickasha, Indian Territory [Okla.]) 1899-current, 1905-01-25
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Eyes first appear among the mednsac
or Jelly fish, among which the lowest
species nave pigment srots only, while
the higher ones have IN addition the
nervous structures and a clear trans
parent lens covering the whole apparatus
In the most perfect form of compound
eye. such as that Of the dragon lT the
lenses are arranged In a series Of crystal
rods closely packed together. but sep-
arated from one another by a film OF
pigment In front the rods are covered
with a transparent cornea the surface nf
which Is moulded into series OF fiat sur
faces, one corresponding TO each Of the
crystal rods. II is from this cirnnm-
stance that an Insect Is said 70 have
several thousand eyes Thus the general
OF convex rctlna having a separate
small lens In frOnt,of each sensitive part
with screen round each lens. so that
a raw Of light can reach the nerves only
when its direction is nearly colncdent
with the axis Of the lens
Two theories Of Insect vision are extant
1.-The older one that each lens forms a
separate eve. and the more recent one
that insects see as In a mosaic. each
lens forming part Of the total picture.
The old view Is supported by the ex-
pertinent OF placing a thin slice OF an
eye under the microscope when the
image Of any object reflected from the
mirror Is seen to be transmitted through
each Of the nexagonal lenses. A rough
nOOel OF an insect eye may ne flhut DF
taking q glass shade OF the form ot a
half sphere. say about sixteen Inches
In diameter. Place the eye mt the center
Of the globe and paint on Its surface
the picture Of the outer world as seen
through IT,
If this painting be divided into snuares
by lines scratched at intervals Of one
eighth of an inch there will be 23.eeJ OF
them. and the proportions are roughly
those found in the eys Of dragon hS,
II now. instead Of the details of the pic
ture on each square. n dab q color be
placed on II corresponding to the sens,.tl
tone. the effect Of the whole will pretty
nearly agree with that OF the original
painting 1t is probably this indistinct
vision that insects actually possess.
Mathematically II may be shown that to
obtain anything like such perfect vision
as human beings eniov an eve construct
ed on the compound tyne would have to
be Of the most ifnpractlcable size.
The retina Is built IN OF the sensitive
termlnations OF the optic nerve. forming
a kind of tesselated pavement with 38 :
00O 600 squares to the square inch. II
our lens were' OF perfect shape, and the
pupil wide enough. the size OF things
which might be seen as distinct objects
would be limited by the distance 0f the
nerve endings in the retina from one an
other. In order that two points may ap-
pear separate to the eve they must sub
tend an angle of about one minute OF
arc: that Is. for instance. that fine lines
ruled one-twentieth Of an inch apart can
be made out to be seDarate at distance
Of four Yards Beyond this the whole
surface has A uniform gray tint. Calcu-
lations clearly show that insects cannot
see nearly as well as this. and their De-
havior to distant objects favors thls
opinion But their eyes have this ad-
vantage. namely that there Is practically
no limit to the nearness OF objects they
can examine. The details OF their Own
antennae probably appear palmer 10
themselves than to US. but objects at
the distance of a foot arpear 10 them
with about the same minuteness OF detail
as world he attained If they were worked
in rather coarse woodwork.