_
: LOCQMOTION IN GASTROPODS
that never more than two waves can” be seen on one.
foot at once. rl‘he foot, therefore, moves forwardin
steps, rst on the right side and then on the left,
resembling that of a person in a sack walk. In Nerit—a
’
‘
_
j the wave begins anteriorly as a single wave whereupon it breaks
«
;
and passes down the right and left sides of the foot to unite as
one wave again at the posterior margin.
These two conditions
of alternate waves, as in Tectarius, and Opposizk waves, as in Nerita.
-
-
will probably be found exemplied in other ditaxic gastrojpods°
In certain small species of Littorina with direct-movements, Vlès ’
has described four parallel sets of waves, .fullling the require—
ments of a tetréttaxic subtype.
This occurs, according to Vlès,
only in connection with the retrograde type of movement
I
have seen no example of it.
'
Among those snails that I have examined, one species, Ilyan—
assa obsoleta (Say), seems to find ne place in Vlès’ classication.
-
This snail is a vigorous, active creeper;
'
Its foot covers a large
area compared with the size of its body.
Anteriorly‘ the foot is
'
truncated and auriculate; posteriorly it is bluntly rouhded. lts
.
.
ventral surface is whitish, ecked over with irregular grayish
_
splotches. In resting, the snail uses chiey the posterior part of
the ”foot, the anterior part being sometimes —inore or less with—Â
drawn into the shell.
In locomotion-the anterior part seems to -
'
be the mOr—eactive.
Notwithstanding the fact that this snail
is very easily observed inactive“ creeping and that its foot is
marked in a most favorable way for. exhibiting wave—like move—
.
.
'
Î
ments,lhavenever”been able to
evidence of such
_
‘
movements
When in locomotion, the Whole”
seems, to ‘glide
tlnoftheantermrvenüalsurface0fthef00t0anshsht Varia—É
'
'
as
…
.
whmhmha maybethechæfmot0r mgansbutonfzestmgthefoet
: LOCQMOTION IN GASTROPODS
that never more than two waves can” be seen on one.
foot at once. rl‘he foot, therefore, moves forwardin
steps, rst on the right side and then on the left,
resembling that of a person in a sack walk. In Nerit—a
’
‘
_
j the wave begins anteriorly as a single wave whereupon it breaks
«
;
and passes down the right and left sides of the foot to unite as
one wave again at the posterior margin.
These two conditions
of alternate waves, as in Tectarius, and Opposizk waves, as in Nerita.
-
-
will probably be found exemplied in other ditaxic gastrojpods°
In certain small species of Littorina with direct-movements, Vlès ’
has described four parallel sets of waves, .fullling the require—
ments of a tetréttaxic subtype.
This occurs, according to Vlès,
only in connection with the retrograde type of movement
I
have seen no example of it.
'
Among those snails that I have examined, one species, Ilyan—
assa obsoleta (Say), seems to find ne place in Vlès’ classication.
-
This snail is a vigorous, active creeper;
'
Its foot covers a large
area compared with the size of its body.
Anteriorly‘ the foot is
'
truncated and auriculate; posteriorly it is bluntly rouhded. lts
.
.
ventral surface is whitish, ecked over with irregular grayish
_
splotches. In resting, the snail uses chiey the posterior part of
the ”foot, the anterior part being sometimes —inore or less with—Â
drawn into the shell.
In locomotion-the anterior part seems to -
'
be the mOr—eactive.
Notwithstanding the fact that this snail
is very easily observed inactive“ creeping and that its foot is
marked in a most favorable way for. exhibiting wave—like move—
.
.
'
Î
ments,lhavenever”been able to
evidence of such
_
‘
movements
When in locomotion, the Whole”
seems, to ‘glide
tlnoftheantermrvenüalsurface0fthef00t0anshsht Varia—É
'
'
as
…
.
whmhmha maybethechæfmot0r mgansbutonfzestmgthefoet