THE PHYSIOLOGY OF LOCOMOTION IN GASTEROPODS. 8/ 



periments in that line would have convinced him of the fallacy 

 of his theory. I have tested the longitudinal muscle of the foot 

 in several gasteropods and my results go to show that there is no 

 difference between the physiology of this muscle and that of any 

 other muscle. On stimulation, either directly or through the 

 motor nerves, the muscle-cells or strands of muscle-cells shorten 

 and thicken in the usual way. These experiments may be per- 

 formed with the greatest ease on the foot of Pleurobranchaa, 

 as the foot musculature of this gasteropod is composed of a very 

 loose meshwork of septa that may be separated the one from the 

 other without sufficient injury to produce extreme contraction. 

 In gasteropods with very compact foot this cannot be done, as 

 the injury of dissection produces extreme contraction. But even 

 when the foot musculature is greatly contracted direct stimulation 





FIG. I. Tracings, V 2 natural size, of the tracks of a snail moving in the manner illus- 

 trated on previous page. The dotted areas are the areas covered by the mucus 

 film. The arrow indicates direction of the motion. Medium-sized animal, moving 

 rapidly. 



with the induced electrical current produces, not an elongation, 

 but a further shortening and thickening of the muscle. In no 

 case does the stimulation produce elongation of the longitudinal 

 muscle strands. 



Jordan (igoi) 1 rejects the theory of "extensile muskulatur ' 

 in accounting for the locomotion in the marine gasteropod Ap/ysia, 

 and ascribes the relaxation or extension of the longitudinal 

 muscle of the foot to the pressure of isolated bodies of the 

 visceral fluid or blood. As evidence Jordan points to small 

 reservoirs or lakelets of plasma in the strongly contracted foot. 

 These lakelets are constricted off from the visceral cavity by the 

 contraction of the muscular septa. A body of liquid thus cut 

 off from the visceral cavity may serve to produce extension of 

 the longitudinal muscle at its anterior border by the force of con- 

 traction of the oblique and transverse muscles at its posterior 

 end. In this way we would have as many isolated bodies of 



'Jordan, H., "Die Physiologie der Locomotion bei Aplysia limacina," Zeitschr. 

 f. Biologic, XL I., p. 196. 



