LOCOMOTION IN GASTROPODS'
161
,
,
,
‘
'
without sucking air through the perforation, thus demonstrating
-
(
that its attachment in locomotion, as in rest, is due to adhesion.
—
,
'
and not to suction.
In fact in a creeping Helix the foot not only
'
does not suck but actually presses on the substrate. ' If, as the”
snail creeps, a bubble of air is introduced under it by a capillaryitube or other means, this air will usually escape at the edge of the
foot in such a way as to show that it was Under
;
]}
sure.
The action of such
demonstrates that the foot as
'
-
-"
a whole is rmly attaChed to the mucous substrate,
fact presses
_
,
against it.
Locomotion in Helix pomatia, then, has to overcome' , '
under ordinary circumstances only the adhesion of the foOt and
-
this is accomplished apparently by the pedal” waves. _In —snails
_
in which the attachment is due tosuction as
to adhesion,
-
locomotion requires that both attractive forces shall have been
.
overcome, but, as suction is muscular, it seems likely that this
would be relaxed somewhat, as seems to be the‘case in Crepidula,
'
_
before locomotion begins.
,
'
,
.
‘
]
How the pedal waves accomplish locomotion is still a disputed
,
_
question.
According to von
p. 181), Who has fol—
lowed Jordan (’01) and Biedermann (705) in many particulars,
?
each pedal wave is formed by the contraction of the longitudinal
_
muscles of the foot and takes the
a 'slight s‘welling on the”
underside of the
Such awave, 38
Uexküll rightly re—
‘
marks, would effect nothing by Way of
some
portion of the foot were Xed. V0n UeXküll_
‘believes
’
that the foot is provided With somesu0hmechamcal deVi0e-as the .
Setae of the earthworm,whmhleslst9JCkV‘ÏaÏdmOVeme‘—ïtWhlle
.
xed
accomphshed
1t1sdoubtfulwhethel1treayapphest0the°asemhanV®n