264
THE BIOLOGY OF FISHES
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go on
the, comparatively soft materials of the
head more and more to the sides.
And most gures
publiShed of these forms seem _to have caught the sh in
the act.
In the deep—sea Teleosts, 'on the other hand, the head is
usually compressed from side to side and the eyes are also.
compressed and large. The latter phenomenon has often
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been called an adaptation to the darkness of the deep sea,
it being assumed that the broader surface would somehow
catch and concentrate any stray rays of light, but the great.
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pressure is a suîcient explanation.- The telesc0pic eyes of
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many deep—sea forms in the young stages are possibly to a
great extent articial, produced by the sudden change to
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less pressure When"the,sh is brought up to the surface.
The eyes of ;the embryOnic Trachypterus, when the eggs
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are taken and_.placed in tanks, are telescopic for two or three
days and then gradually drop back into their places.
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From the foregoing it Will
seen
that thestructureS
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which arise from the mOVements and interaction With the
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external physical medium can” hardly be called adaptations,
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unless they are further turned to good account by the sh
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itself.
A stone sinks in the water While'the cork oats,
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yet we do not say thatthey are adapted to these purposes
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until We use them.
In the same Way it does
seem right
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to say that pelagic eggs are adapted to oat and demersal
eggs
to remain at the bottom, When theSignicarit;m€aning
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is,that the density Of the
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Further, _tofsay that the Hei*rigis
the,
a demersal, and the :Carp to freshWater, adds
nothingï‘to the understanding of the‘faéts‘; When we have —
do not require to
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the"word
—
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,
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? Thè”_chief diîcülty abôùtthè Word is,
thatin
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or combination of
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CircumStances,”eäçternalfto the
Which has
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“adapted
-’ ’ it to suit the conditions.“ If {it be
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that‘thi$ View has no p‘rerogative‘- to the 'use of the-WOÏd'äl—id
â , ï‘thatÏadaptations may
arise in a diffèrth way; frorthe
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