160 | 2G. HP AR Ke 
THE GASTROPOD FOOT AS A LOCOMOTOR ORGAN 
Locomotion by the gastropod foot, is not dependent upon 
ciliary action but is a muscular operation as shown by Dubois 
and Vlés (07). The precise way in which the movements of loco- 
motion are accomplished can best be made out by examining good 
examples of direct and retrograde movement. The first is well 
exemplified in Helix pomatia and Limax maximus; the second in 
Chiton tuberculatus and Dolabrifera virens. 
In an expanded and actively creeping Helix pomatia, the foot 
may measure as much as seven to eight centimeters in length 
by two and a half in width. Over this a succession of transverse, 
dark-brownish waves run from posterior to anterior. At any 
instant there may be as many as ten or a dozen such waves on the 
foot. Each wave is separated from its neighbor by a space equal 
to about three-times its own thickness. The waves travel over 
the foot in about thirty seconds, or at a rate of a centimeter in 
seven to eight seconds. These records, taken from a normal in- 
dividual, agree fairly well with those given by Bohn (’02) and by 
Biedermann (’05). 
As the snail creeps, it spreads from the mucous gland at the an- 
terior edge of its foot a broad path of slime over which it makes 
its way. An active snail marks its course in this manner by a 
long track of slime. A somewhat exhausted snail, when placed 
upon an appropriate substrate, will almost always creep far enough 
to lay a mucous path that will subtend the whole of its foot, after 
which it will cease creeping. If it is removed to another position, 
it will usually repeat this operation, but it will seldom creep far- 
ther. This habit is doubtless connected with the effectual at- 
tachment of its foot to the substrate. | 
Locomotion in Helix, like that in other pulmonates (Kiinkel, 
’03), is apparently inseparable from the wave movement of its 
foot. When a snail is placed upon a glass plate preparatory to 
creeping, it lengthens and expands its foot; almost immediately 
thereafter pedal waves appear and the animal begins to move 
forward. Such a snail will creep over a perforation in a glass plate 
