LOCOMOTION IN GASTROPODS 169 
waves, because in the gallop the body waves of this species, as 
reported by Carlson, were retrograde whereas the pedal waves in 
all Helices thus far reported are direct. 
SUMMARY 
Ordinary gastropod locomotion is accomplished either without 
pedal waves (arhythmic) or with pedal waves (rhythmic). In 
rhythmic locomotion the waves may run from posterior to ante- 
rior (direct) or the reverse (retrograde). The foot may exhibit 
one (monotaxic), two (ditaxic), or four (tetrataxic) series of 
waves. In the ditaxic foot the waves may be alternate or oppo- 
site. 
The gastropod foot is an organ of attachment through adhesion 
(mucus) or suction, or both. 
The pedal wave is an area of the foot that is lifted off the sub- 
strate as compared with the rest of the foot and thereby freed 
more or less from adhesion. It is also the region of the foot that 
moves forward, the rest of the foot remaining temporarily station- 
ary. Locomotion is the cumulative result of local forward motion 
on the part of one section of the foot after another till the whole 
foot has teen moved. The same type of muscular movement as 
that seen in rhythmic locomotion can be present in a diffuse form 
(not wave-like) in a gastropod foot and will result in locomotion. 
