…
H
H
H
H_
…_
.
LOCOMO'I‘ION IN GASTROPODS
_
167
point on the foot is lifted, moved forward, and set down again
and thus the foot, and with it the animal as a whole moves for—
ward.
From this theoretic consideration, it is evident that the
theory of pedal—wave action advanced in the preceding paragraphs
'
is entirely consistent with such an arrangement of muscles as has
?
long been known to occur in the gastropod foot.
Vlès (’07) has called attention to the fact that the majority of
'
theories as to the locomotor action of the gastropod foot apply
‘
‘
only to the direct type of movement and do not take into account
‘
the retrograde type.
The theory put forward in this paper is
_.
believed to apply equally well to both types. Among retrograde
\;
gastropods, Chiton tuberculatus is an excellent example. This
mollusc uses its foot as a sucker, but nevertheless can creep with
considerable rapidity.
lt exhibits, as a rule, not more than two
?
waves on the foot at a time; these course posteriorly at the rate
_
—
of about a centimet€r in ve seconds.
In a Chiton creeping over
a glass plate, the wave when viewed from the side can be seen to be
"
’
Î
an area lifted well off the substratef This feature is much more
'
-
conspicuous in Chiton than in any other mollusc that I'have ex—
amined.
As in the pulmonates, the surface of the Chiton foot in
-
direct contact with the substrate is motionless; that in the wave
_
Î
‘
area moves forward.
At any moment about one quarter of the -
:
'
Chiton foot is moving forward While the —ar£imal supports itself on
*
.
the remaining three quarters.
-
_.
In Dolabrifera the foot is pear—shaped in outline with the
‘
'
rounded end posterior.
It is about $…. m length.
In creeping;
_
=
___—
one to two waves can be seen on its
each wave
)
‘
ff
the length of the foot in
ASîChit0n,
the waves can be clearly seen
the f00'G -îS lifted
*
completely from the
_
°
1mly applied;
the
WäV@
.
?
area it can:be seen
Of.
-
-
—
…
‘
the foot 1113 is mot1nlessThet0taîWâ‘ïêalealsabout0nehalf ==]—
the]total area of thefoet
;
The conditionsm0hltonandm@labllferaareeSænmav
H
H
H
H_
…_
.
LOCOMO'I‘ION IN GASTROPODS
_
167
point on the foot is lifted, moved forward, and set down again
and thus the foot, and with it the animal as a whole moves for—
ward.
From this theoretic consideration, it is evident that the
theory of pedal—wave action advanced in the preceding paragraphs
'
is entirely consistent with such an arrangement of muscles as has
?
long been known to occur in the gastropod foot.
Vlès (’07) has called attention to the fact that the majority of
'
theories as to the locomotor action of the gastropod foot apply
‘
‘
only to the direct type of movement and do not take into account
‘
the retrograde type.
The theory put forward in this paper is
_.
believed to apply equally well to both types. Among retrograde
\;
gastropods, Chiton tuberculatus is an excellent example. This
mollusc uses its foot as a sucker, but nevertheless can creep with
considerable rapidity.
lt exhibits, as a rule, not more than two
?
waves on the foot at a time; these course posteriorly at the rate
_
—
of about a centimet€r in ve seconds.
In a Chiton creeping over
a glass plate, the wave when viewed from the side can be seen to be
"
’
Î
an area lifted well off the substratef This feature is much more
'
-
conspicuous in Chiton than in any other mollusc that I'have ex—
amined.
As in the pulmonates, the surface of the Chiton foot in
-
direct contact with the substrate is motionless; that in the wave
_
Î
‘
area moves forward.
At any moment about one quarter of the -
:
'
Chiton foot is moving forward While the —ar£imal supports itself on
*
.
the remaining three quarters.
-
_.
In Dolabrifera the foot is pear—shaped in outline with the
‘
'
rounded end posterior.
It is about $…. m length.
In creeping;
_
=
___—
one to two waves can be seen on its
each wave
)
‘
ff
the length of the foot in
ASîChit0n,
the waves can be clearly seen
the f00'G -îS lifted
*
completely from the
_
°
1mly applied;
the
WäV@
.
?
area it can:be seen
Of.
-
-
—
…
‘
the foot 1113 is mot1nlessThet0taîWâ‘ïêalealsabout0nehalf ==]—
the]total area of thefoet
;
The conditionsm0hltonandm@labllferaareeSænmav