LOCOMOTION IN TWO SPECIES OF THE GASTROPOD 



GENUS ALECTRION WITH OBSERVATIONS 



ON THE BEHAVIOR OF PEDAL CILIA. 



MANTON COPELAND, 

 SEARLES BIOLOGICAL LABORATORY, BOWDOIN COLLEGE. 



INTRODUCTION. 



In a paper on locomotion in gastropods Parker ('n) has 

 pointed out that the mud snail, Alectrion (Ilyanassa) obsoleta 

 Say, exhibits no rhythmic pedal movements such as are readily 

 observed in most snails, and concludes that progression is ac- 

 complished by arhythmic muscular activity. He writes: "The 

 movement of the foot of Ilyanassa has a most striking resemblance 

 to that of the foot of a planarian in which cilia may be the chief 

 motor organs, but on testing the foot of Ilyanassa with carmine 

 suspended in sea water, not the least evidence of cilia could be 

 discovered." In subsequent accounts of gastropod locomotion 

 Alectrion obsoleta has been cited as representing the only definitely 

 known case of arhythmic movement. Recently, however, 

 Crozier ('19) has reported another example, that of Conns 

 agassizii from Bermuda. 



In the course of studies on the reactions of Alectrion I became 

 interested in the locomotion of the animal and tested the foot for 

 cilia by dropping carmine grains on its ventral surface. Much 

 to my surprise the carmine was carried down the foot, and when 

 the latter was examined under the microscope the under surface 

 was found to be covered with cilia. Another related species, 

 Alectrion (Tritia) trivittata Say, w r hich showed no evidence of 

 pedal waves likewise proved to have a ciliated foot. 



That cilia occur on the feet of certain species of gastropods has 

 been know r n for some time, but that they function as locomotor 

 organs, however, has been questioned, and I believe that no 

 detailed study of their behavior has been made. Olmsted ('17) 

 has recently reported finding cilia on the feet of three species of 

 marine snails from Bermuda, which showed no evidence of pedal 



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