PEDAL LOCOMOTION OF APLYSIA CAL1FORNICA 



141 



In discussing the locomotion of gastropods two important 

 questions must be considered: first, what part of the foot is at 

 any moment concerned with locomotion, and, secondly, where 

 and how is the foot anchored. On both these questions impor- 



Fig. 1 A, side view of an Aplysia at the moment the anterior end is raised 

 from the substrate as the initial step in the formation of a wave; the middle of 

 the foot is attached and a wave is disappearing at the posterior end. A', ven- 

 tral view of the foot, narrow at the two free ends and broad at the attached 

 middle, where fragments of pebbles and fragments of shell are held by suction. 

 B, side view at the moment the two ends are attached and the wave has reached 

 the middle. B', ventral view of the foot, showing the narrow free middle and the 

 broad attached ends, to which pebbles and fragments of shells are held by 

 suction. 



tant evidence can be had from Aplysia, and in dealing with the 

 first of them direct observation is all that is necessary. 



A close inspection of the movements of the foot of Aplysia is 

 best made on a specimen creeping in a large glass aquarium 

 accessible to observation from several sides. In a specimen so 

 situated each pedal wave can be seen to start at the anterior 



