author's abstract of this paper issued by THE BIBLIOGRAPHIC SERVICE OCTOBER 5. 



CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT 



HARVARD COLLEGE. NO. 297. 



THE PEDAL LOCOMOTION OF THE SEA-HARE 

 APLYSIA CALIFORNICA 



G. H. PARKER 



ONE FIGURE 



The way in which snails use the foot in locomotion is by no 

 means clear, and the discussion of this subject has led to a number 

 of diverse views. The cilia found covering the foot of some gas- 

 tropods have been supposed by a few investigators to be the 

 means of locomotion, but the majority of students have main- 

 tained that the pedal muscles are the organs concerned with this 

 form of movement. These muscles usually act in rhythmic 

 fashion producing a series of waves that course over the foot, 

 and by this means it is believed tihat the snail is enabled to 

 move from place to place. The pedal waves of most snails are 

 of small dimensions and the exact way in which they serve in 

 locomotion cannot easily be seen. In the large California sea- 

 hare, Aplysia californica Cooper, these waves are of very un- 

 usual size and progress at such a rate that they give ample op- 

 portunity for the examination of many details which in most 

 snails are quite hidden. I have had the opportunity of studying 

 this animal at the Scripps Biological Institute, La Jolla, Cali- 

 fornia, to the staff of which I am under obligations for many 

 courtesies. 



Aplysia californica is found in considerable numbers among the 

 rocks at low tide on the beach to the north of the Scripps Lab- 

 oratory. Full grown individuals average about 25 cm. in length. 

 In such specimens the foot proper is represented by a band run- 

 ning lengthwise the ventral surface and about 23 cm. long by 

 2 cm. wide. This band, however, is capable of contracting to at 

 least one-half its original length. The locomotor waves, which 

 reach across the whole width of the foot, begin at the anterior 



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