ECONOMY. OF THE BODY—H
165
more recently by Schiemenz (1924), we know that some
shes at any rate are able to distinguish colours, T hus,
,
Frisch gave some specimens of PhoXinus variously coloured
meats and found that red, wasnot favoured, the yellow and
grey colours being preferred.
“
,
'
…
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The production of coloured pigment Within the tissues
_
of the sh is a separate, yet to *someextent close‘lyielated
problem. Pigment is a product of the radiant eergyofthe
sun, on the one hand,“ and of the living processes
other, The silvery iridescence comes from guani (a waste
product), or this and lime, which in places is packed tightly
into a compact layer in the-body, as in the retinaof the eye ;
but the colours red, yellow, black, and blue come appareny
from the oxidation of organic substanceswithin certain
connective tissue cells (chromatophores). These cells are
'
branched just like the dendrites of the nerve cells and the
protoplasm within Seems to retairi the amœboid power of
expanding adcontracting, thus spreading out: or narrowing
‘
the pigment.— «These stream mOvements, Pouchet‘ found,
were
currents, the nervous = system,
thus by death—or theloss ofCentral
the
remain
.
like the muscle
,
on the other hand, the “presence—of rS_olari :energygenh’aces,
,
the metabolism—vthin
—-CaùSing an increase -
of pigment formation, and a more—livelÿ play of colour
ensues.
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'
'
,
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The negation of colour (black or white) is found in deep—_
sea shes or cave shes which live in darkness.
But whilst
the paleness of the cave shes may be ascribed to enfeeblement of the whole system and especially to the poverty of the
blood, this Cannot be said of the deep-sea shes. Here
;
f
intensely : black pigment probably comes from excessive"
_
metabolism and: thegdisruption…or
make
taken—}.by'à—the
'
”
regulating the .playiof colour,
thié,_poWeri
"
,
;