334
THE BIOLOGY OF FISHES
(Schäer) Eels were carried to a distance away from water
and then set free.
They invariably found their way to
the nearest stream, though miles away, and that With hardlyany hesitation.
Is this tropism or a water-sense ?
'
7
’
Reex actions or motor responses
to partiCular' stimuli
»
embrace a wide range of activities.
Here we may think
,
of the brain and spinal cord as a sort of mirror. From
without a stimulus passes along the sensory chan”nelsto
this mirror, whenCe it is reected on to the muscles without
any
deliberation or consciousness of what is happening. ÿ
We instinctively close the eyelid when anything approaches
Ÿ
.;
too near, the hand closes on seizing an object, the mouth_
opens and shuts with the entrance of food, and so on.
The
}
…
nerve paths“from the sense organ receiving the stimulus to
'
:
the muscles responding form a continuous course.
'
Many of these simple reex ”actions can be studied in”
'
the shes of an aquarium. When a sh is -resting, we Can '
êï
'
see the breathing valves opening and closing- to take water
'-—
into the mouth, a slight ppling along the vertiCal ns Or
f
a heating of the pectorals shows how the sh is balancing' }f
itself, and when it moves we can see how the swing of‘the
tailis sending it, forward. It does not matter what sense is
'
,
stimulated, the balance, smell, -or eyesight, the response
seems to come automatically.
’
' _
_
…
Î,
The reexeS are very complicated when more than °One
_
set of .muscles come into acti0n.
'
To get at its
1
sh may have to turn and twist about or Change its direction
.
up and down in the water.The-central organisation in…
_
the__brain
__a part
the' inapprôpriate
'
muscles from acting;— _îUsing the=simile aboVe, We may say ' l
that several
are inïtheîpath of the impression, bi1t
'
the C0ïr€C‘t'0'ne
the—right time. But the 'sim‘ilçæ
'
'
has to
be changed,.ŸwhenŸz'we Come" to istill higher leVels of '
action, whènthe‘sh,fof “€Xâmpl'ëiha‘s Several cOurses open
_to it, as_when 0ered “r'diêfê—nÏt 'fOOdS”, and'denitelyselec‘ts '
'
…
only one of them. In'hislexperiments on='Eels Schiemen'zÏ
,
pressed some fOodwith thèngers of one hand,Ïthenplaœd
,
,
both hands, no f00dninfîeither,
—'Thé Eds ,
'
.
THE BIOLOGY OF FISHES
(Schäer) Eels were carried to a distance away from water
and then set free.
They invariably found their way to
the nearest stream, though miles away, and that With hardlyany hesitation.
Is this tropism or a water-sense ?
'
7
’
Reex actions or motor responses
to partiCular' stimuli
»
embrace a wide range of activities.
Here we may think
,
of the brain and spinal cord as a sort of mirror. From
without a stimulus passes along the sensory chan”nelsto
this mirror, whenCe it is reected on to the muscles without
any
deliberation or consciousness of what is happening. ÿ
We instinctively close the eyelid when anything approaches
Ÿ
.;
too near, the hand closes on seizing an object, the mouth_
opens and shuts with the entrance of food, and so on.
The
}
…
nerve paths“from the sense organ receiving the stimulus to
'
:
the muscles responding form a continuous course.
'
Many of these simple reex ”actions can be studied in”
'
the shes of an aquarium. When a sh is -resting, we Can '
êï
'
see the breathing valves opening and closing- to take water
'-—
into the mouth, a slight ppling along the vertiCal ns Or
f
a heating of the pectorals shows how the sh is balancing' }f
itself, and when it moves we can see how the swing of‘the
tailis sending it, forward. It does not matter what sense is
'
,
stimulated, the balance, smell, -or eyesight, the response
seems to come automatically.
’
' _
_
…
Î,
The reexeS are very complicated when more than °One
_
set of .muscles come into acti0n.
'
To get at its
1
sh may have to turn and twist about or Change its direction
.
up and down in the water.The-central organisation in…
_
the__brain
__a part
the' inapprôpriate
'
muscles from acting;— _îUsing the=simile aboVe, We may say ' l
that several
are inïtheîpath of the impression, bi1t
'
the C0ïr€C‘t'0'ne
the—right time. But the 'sim‘ilçæ
'
'
has to
be changed,.ŸwhenŸz'we Come" to istill higher leVels of '
action, whènthe‘sh,fof “€Xâmpl'ëiha‘s Several cOurses open
_to it, as_when 0ered “r'diêfê—nÏt 'fOOdS”, and'denitelyselec‘ts '
'
…
only one of them. In'hislexperiments on='Eels Schiemen'zÏ
,
pressed some fOodwith thèngers of one hand,Ïthenplaœd
,
,
both hands, no f00dninfîeither,
—'Thé Eds ,
'
.