THE PHYSIOLOGY OF LOCOMOTION IN 

 GASTEROPODS. 



A. J. CARLSON. 



While studying the physiology of the molluscan heart I inci- 

 dentally observed in the snail a mode of locomotion which would 

 seem to explain the mechanism by which the series of waves of 

 contraction and relaxation of the sole of the gasteropod foot in 

 locomotion are produced. The musculature of the foot and the 

 ordinary movements of locomotion of land gasteropods by a 

 series of alternating contractions and expansions, passing as 

 waves over the sole of the foot in the postero-anterior direction, 

 has been described by Simroth (1878, iS/9). 1 Simroth's obser- 

 vations were made principally on Helix and Liinax. In attempt- 

 ing to correlate the form and sequence of these waves of locomo- 

 tion with the structure of the musculature of the foot Simroth 

 concludes that they cannot be produced by the separate or com- 

 bined contractions of the oblique and the transverse muscular 

 strands. The cause of the extension of the foot is to be sought 

 in the active extension of the longitudinal musculature ; that is, 

 when the muscle-cells making up these strands contract they 

 elongate and decrease in thickness. These he therefore calls 

 " extensile muskulatur " in contradistinction from the oblique 

 and the transverse muscle, which is of the ordinary contractile 

 type. 



This theory of " extensile muskulatur" may explain the series 

 of elongations of the foot in locomotion, but the question is, Is it 

 true? The theory may without much difficulty be put to the 

 experimental test by any one interested. Simroth does not show 

 that the muscle-cells making up the longitudinal musculature of 

 the foot increase in length and decrease in diameter on direct 

 stimulation or on stimulation of the pedal nerves. A few ex- 



1 Simroth, H., "Die Thatigkeit der willkiirlichen Muskulatur unserer Land- 

 snecken," Zeitschr. f. wiss. Zoo!., XXX., p. 166 ; "Die Bewegung unserer Land- 

 snecken, hauptsachlich erortert an der Sohle des Limax," Zeitschr. f. wiss. Zoo!., 

 XXXII., p. 284. 



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