Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1912-10-28
PROTECTIVE MIMIcRY.
Birds and Beasts Take on Colorin9 OF
Thsir Surroundings.


Every one nowadays is familiar with
the theory of protective oration--how
a green caterpillar is green because he
lives on green leaves, and is thus better
protected from his enemies. The exact
mechanism, however, by which the
skins of certain Insects, birds, beasts
and fish come to resemble their sur
roundings has never been discovered.
Recent Investigations and the theories
to which they have given rise throw
some light on it, Certain fish are found
to change the spots on their skin to
match spots on the bottom of the tank
where they are kept If their eyes are
blinded on their optic nerves are para
lyzed. this imitation ceases. The eye,
therefore, seems to be an important
part of the machinery. it may therefore
be that the green caterpillar is green be-
cause he continually gazes on green
things. Says a writer in the Revue
Scentifique paris. July 49,
Summer Tan American naturalisD has
shown that not only does the skin of
the fish reproduce faithfully the general
color of the bottom. but that it is able
even to initiate quite complicated de
PN'NN~tii
an aquarium in which are turbots round
or square figures or stripes, alternately
black or white. we see the same designs
reproduced on the fishes skins. These
designs, of course. owing to anatomical
reasons, can not be of absolute geome-
t.Ical form.
"Ponchet discovered tina. the 'adapta-
ton to the bottom absolutely disappears
when we destroy the fishes sight, or
when we prevent the formation of reti-
nal images by disturbing the retroactive
media of the eye. Loeb concludes, in
recent publication, that the agreement
between the design and coloration of the
skin and those of the bottom is brought
about through the retinal image that,
in other words, the phenomenon hitherto
designated as 'homocleromy and adap-
tation, is nothing else but transporter
ton of the retinal image to the skim
Several authors assert that the retinal
image is projected upon the brain, and
it appears well established that In vis-
ion an image is formed not only on the
retina but also on the substance of the
brain; although there are still differences
between authors as to the precise region
where the visual sphere is found. Now
the facts of adaptation in fishes are
able according to Loeb, to clear up the
mechanism of vision 1t has been seen
that the image on the bottom cannot be
reproduced by the skin except through
the intermediary of the .retina. On the
other hand, we know that the destruc-
ton of the optic fbers or ganglia pro-
duce the same effect as the extirpatlon
of the eyes. Finally, it has been estab-
lished that cutting the sympathetic
nerves that lead to the pigmentary cells
of the skin also prevents the formation
of the skin images. The road by which
the retinal image is transferred to the
skin is thus traced And since, says
Loeb, we may show the existence of the
image of the object on me fishes retina;
as we may also demonstrate that the
image on the skin is the reproduction Of
that on the retina and not of the object
itself: as, on the other hand, the trans
fer of the retinal image to the skin is
made by the optic nerve, Ii is evident
that the image projected on the skin
passes through the central ganglia of
the optic nerves.
"An image is formed of a multitude of
points of different luminous intensities,
whose relations are determinate and
characteristic for a given object. In the
case of a fish placed, for example, on a
given surface, there Is produced on the
retina a particular disposition OF lumi-
nous points and on the skin similar
arrangement. Loeb asserts that each
point of the retina is an Initiative point
that gives rise, through the intermediary
of an optic fiber, to corresponding
point of these latter serves in turn as
an Initiative point which influences in
determiHate fashion, through special
nerve fiber, a Elementary cell, or a
group of such cells, on the skin. 1t is
difficult to assert. having In view the
structure of the retina, that during the
transfer of the retinal image to the
skin, the arrangement of the luminous
points corresponding to a given object
vanishes in the optic nerves and ganglia.
There must therefore be in the primary
optic ganglia particular distribution
of rritative intensities, corresponding
to that of the luminous points on the
retna and capable of being itself con-
sidered as an image. These deductions,
which are extremely suggestive, lead
Loeb to put forward the hypothesis that
vision is a sort of telephotography as
well in color as in form. Literary DE-
gest.