Idaho semi-weekly world. [volume] (Idaho City, Idaho Territory) 1875-1908, 1888-11-16
slGftT or sPinEns


Prof. Rfatfau Claims Tt5Nf II noes Not
Exceed 9 Few Inches.
Prof. Plateau has been examining
the organs Of sight among The Araeh-
nida Their development in this re-
spect IL lar from uniform. Some. ike
she scorpions. shnn the daylight. and
must depend upon chance or upon
their other senses for the capture OF
their prey, Others, like the majority
Of the true Araehnida- hang out snares
for irsects. wEile other families In this
group seek the light and live by hunt
ing. In these latter the visual percep-
lions have reached the highest grade
l,f development.
Thanks to the numerous eyes Of tfle
spider, it il popu,ariy credited With
excellent sight Naturaiists. however,
have long ago refuted this error. and
shown that these eyes. In virtue Of
their curious dimorpuisn dis
covered BY Grenacher.s are very
/ Indifferent Instruments. or at
least that their possessors must
be very short-sighted Muller and
Lacordaire find that spiders see dis
tlnctly only to a very short distance.
Dnges thinks that If spider takes ref
uge In It's hole at the approach Of q
man. even at the distance OF fathon.
it 10 not necessary to suppose that it
has any distinct vision at such a dis
| lance. but merely recognizes moving
masses.
The researches Of Al Plateau have
not merely confirmed these surnises.
but have extended them in an unex-
pected manner. His minute expert
ments have been extended to various
species of spiders. and have led him to
conclude that the distance at which
vision is sufficiently distinct TO induce
spider to capture lis prey il about an
inch in the most sharp-sighted species.
and that the vague perception of move
ments to Epib.emum seenicum does
not exceed five or six inches.
The following observations. which
the reader may verify In any garden
on fine day in the latter part OF sum
mer- fully confirm the statements of
| 81 Plateau II blue-bottle falls into
the web of geometrieal spider (Epeira
! diadema). she does not rush right to
/ the spot, but applies her feet in rapid
succession 10 the radii of the web. and
thus ascertains by touch the exact
position Of the struggling prey. If
I the web is gently touched with blade
of grass or soft feather she PUSHES to
/ the attack. and does not at once per-
ceive the fraud but actually seizes the
useless object.
We have seen harry-long-legs get
entangled in cobweb in his blunder-
ing flight. and just manage to extrieate
himself in time, leaving leg behind
him as forfeit. The spider. hurry
ing up. seized the leg. NOT noticing
! that it was bodyiess, ran to the other
/ end and then back TO the first. only
learning by very close examination
that the booty was just leg and
! nothing more. No creature having a
| moderate range Of vision could be SO
/ deceived.
| The conclusions of NJ Plateau are
| hat the Arachnida in general perceive
he movements of bulky bodies from a
| distance The So called hunting sui-
| iers, such as the Lyeosse. are probably
he only ones which see the movements
# small objects They perceive such
movements within a range. according
10 some observers. at from one inch to
foot, but which, according to Plateau,
Toes not exceed six inches Even al
such small distances their sight Is no;
distinct Weaving spiders havea very
eGor sight at any distance. and only
letect the presence and the position oil
heir prey by the vibrations Of the web.
A Mistake Often Made.
Men eften conceive that they have sur
EaoUntf j a. obstacle or overcol-s an eEi
when in fact they have merely got use>
o. accustomed TO it. 'sHow are Won now
adaysS asked retired physician of
friend WHO had been suffering from 81
s1ninoas complaint "Oh. an betteri
| was the answer, unless it is that | an
only getting used TO shis one thing