The Fulton County news. [volume] (McConnellsburg, Pa.) 1899-current, 1903-09-09

light. Taking their cue from the botan-
lists. who have Investigated this pho
nomenon closely. the Psychologists
have found that many animals behave
exactly like plants in this regard, re-
spending TO the direction of a light wave
with precision almost equal to that
of the needle to the magnetic current.
Especially is this true of myr,ads OF
the little organisms which everywhere
abound in sea water, and the study
of their activities has been fruitful
of suggestive results. Some OF these
animals are positively and others mega.
lively heliotropic-that is. some are
compelled TO go towards the light and
others away from it; and. strange to
say. some are positive ut one time and
negative at another.
OF the negative form. the larvae Of
the great horS 1Shoe crab arc COOL on
amplcs. If dish of sea water in
which these larvae are swimming be
placed in such Il position that it is
Illuminated by rays of liGht from Il sin
gle window. ii will be noticed that
soon the specimens have crowded to
the side fartheSt from the window.
That their position has been deter
mined by the direction of the light
waves and not merely by differences
of illumination has been established
By several methods Of proof.
\ DEMONSTRATION.
Tn +ln ,v,r,,. =, 4, eh,lla.,. J;s', ,,o
placed Il number Of specimens which
manifest the tendency to swim away
from the light. Over the dish is placed
Il hollow prism filed with Il somewhat
Opaque liquid. In the shutter is n
window through which the apparatus
is illuminated and light from all other
sources is excluded. With this ar
rangement the darker side of the dish
is the one toward the window, be-
cause the thick side of the prism cuts
out Il larger proportion of the light;
but the direction of the rays entering
the water is practically the same as
it would be with the prism removed.
Without the interceptlrg prism. the
animals. being negatively heliotropic,
collect at the dar.; side of the dish
that is. the side farthcst from the Win
dow. When the prism is put into place
the animals do not collect at the dari;
Uhe window side of the dish, but
again proceed directly in the course
of the light rays--that is TO say, they
swim from the window side. which,
by this arrangement, is relatively dark.
to the room side. which is relatively
bright BY similar methods it has been
shown that certain other organisms are
positively heliotropic; they move to-
ward the source of light, not because
the direction of the light rays deter
mines their movements: and this oc-
ours even when the movement takes
them from bright to dim light
BEYOND ANIMAL CONTROL.
1t is no longer rational to speak of
such movements as voluntary, or to
classify the forms which exhibit them
by such anthrOpomorphlc terms as
dark-loving or light-loving. The pro-
in the candle because of its excessive
folly, but because of its intense hello.
tropism. If the moth is a conscious and
moral agent, its sin does not consist
in the act of rushing into the fame
but in going near enough to allow the
light rays to set in operation processes
beyond its control. Here the social re-
fc-t@er may easily append a moral.
One OF the most curious facts in the
effect of light is that upon certain ami
mails its action Is reversible. Thus the
larvae of some of the barnacles are
positive to dim and negative to bright
light. Under the influence of the rays
which penetrate the water they are
compelled to swim toward the surface.
Before reaching it, however, the in
creased intensity of the light changes
4 IN TO the negative condition and
they swim downwards, until in the
weak illumination they again become
positive. Thus they go dancing up
and down, the plaything of physical
'orces.
POSITIVE AND NEGATIVE.
The larvae OF Il certain maaine worm
nre still more suggestive examples Of
this Kind of change. At ordinary room
temperature they collect on the side
NJ Tho aCua"ium farthest from the win
dow. If the temperature is lowered
to , C,gress C., o" G degrees c., they
migrate 70 the window side. Allow
Tue water 10 become warmer than
degrees c.. they 20 back to the dark
side. There are other animals which
Frc negative N tho presence Of sufii-
cieus oxygen supply, but become posi-
I've In lis absence, and there are forms
whose helio;ropism may be reversed
ty q change n tho concentration of the
eea water.
II IL evident that through one agent,
light, nature can exert an inexorable
power over many organisms. driving
them hither and thlther. either in long
migratlons, or IN whirlng, dancing
movements. The interplay Of forces
must always be exceedingly complex.
their resultant changing with each
change OF attitude. OF place. or of con-
&ition on the part of the organism.
1t f. this complexity which gives the
rDpearancc of freedom of purpose. of
work and play. TO the behavior os
tli0se forms. while in reality they are
obedient 20 an incxorablc tyrant.