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162
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G… H. PARKER
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be slipped Over a glass plate more easily forward than backward,
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just as an earthworm can‘ be drawn over an appropriate surface Î
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more easily headward than tailward.
I must confess that i have
not been able to
myself that there is any difference
in this respect, in Helix pomatia or Limax maximus; both
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to slip over the glass forWard and backward with equal :
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case.
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Moreover, the view advanced by von Uexküll is based upon
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what I believe to be a somewhat erroneous conception of the pedal
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wave.
Biedermann (’05, p. 11) pointed out that the foot of Helix
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pomatia has great advantages over that of many other
p0ds for studies of this kind because of the numerous small specks '
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contained in its outer layer. These specks can be discerned clearly
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by means of a hand lens and they give a true picture of the move—
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ments of the foot;
As watched through a plate of glass over which
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the_animal is creeping, they can be seen, as Biedermann has de—
'scribed, to move momentar—ily forward, then come to rest, and then I
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again-to move forward.
This is best demonstrated on a sheet of
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glass on which there are numerous scratches. - Such scratches
serve as landmai*ks and— by them it canbe seen that the minute _
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specks in the foot do remain essenti”ally xed in position and then;
momentarily move:
for a brief period a
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position of rest, When
in relation to the“
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foot-as a whole, it is ev1dentthatthef0rward motion
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in the dark W&VGS andtha’oquïescencelscha1actensmc of the
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intermediate ghterfporüonsezofthefeetEach Wave—them 1sa
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pulse- Of -:forward' motion
rest@fthef@0t » _ Ï is momentauly
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quiesœnt- ;The area @@V6‘1ïedbythewaves1spmbablya fourth
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01? & f‘fth _of
therefore
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