LOCOMOTION IX GASTROPODS. I2/ 



waves, and attributes their locomotion to ciliary action. Since, 

 however, it is held that progression may be brought about by 

 muscular activity without the appearance of pedal waves 

 (arhythmic locomotion), the presence of cilia and the absence of 

 waves does not signify necessarily that locomotion is accomplished 

 by cilia. It is conceivable that pedal cilia have some other 

 function, such as freeing the foot from foreign material or dis- 

 tributing mucus. If some such conception of ciliary function 

 had not been held by students of gastropods, movement by 

 ciliary action should have been recognized long ago as unques- 

 tionably constituting one type of locomotion in these animals. 

 Walter in 1906 described the mechanism of locomotion in the 

 pond snail, Lymnceus elodes Say, as consisting of "a complex 

 muscular foot clothed on the ventral surface with cilia which 

 act on a mucus track," and did not record finding any pedal 

 waves, yet this case, as far as I know, has never been cited as 

 substantiating the theory that gastropod locomotion may some- 

 times be effected by cilia. 



In view of these facts it seemed desirable to investigate in 

 some detail the behavior of the cilia on the feet of Alectrion in 

 the hope of throwing light upon the possible relation between 

 ciliary action and locomotion. The work was carried on at the 

 Marine Biological Laboratory at Woods Hole, and I wish to 

 express my gratitude to the director, Dr. Frank R. Lillie, for 

 his kindness in granting me the facilities of the laboratory. 



CILIARY BEHAVIOR. 



Alectrion trmttata. The foot of Alectrion trivittata in an 

 individual of medium size measures 10 or 12 mm. in length by 

 4 or 5 mm. in width. The anterior end is truncated and auri- 

 culate. Back of the lateral, pointed processes the foot is nar- 

 rowed somewhat before it expands and tapers toward the pos- 

 terior end, which is bifurcated and bears two small tentacles. 

 It is more slender than the foot of Alectrion obsolete, and consider- 

 ably thinner, a feature which makes the species a favorable one 

 for the study of ciliary activity under the microscope. 



As soon as it was recognized that the under surface of the 

 foot was ciliated the question arose: Were the cilia active during 



