THE PHYSIOLOGY OF LOCOMOTION IN 

 GASTEROPODS. 



A REPLY TO A. J. CARLSON. 



DR. HERMANN JORDAN, 

 (UNIVERSITY OF ZURICH). 



In No. 2 of Vol. VIII., of this BULLETIN, A. J. Carlson pub- 

 lishes a note on locomotion in gasteropods. He, at first, tries to 

 show that my opinion concerning the mechanics of locomotion 

 in Aplysia 1 is wrong. On page 87 he says : " Jordan (1901) re- 

 jects the theory of ' extensile Muskulatur' in accounting for 

 the locomotion in the marine gasteropod Aplysia, 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 con- 

 stricted 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 contraction of the oblique 

 and transverse muscles at its posterior end. In this way we 

 would have as many isolated bodies of blood being gradually 

 pushed from behind forwards in the foot as there are areas of 

 relaxation on the sole of the foot. The presence of isolated 

 bodies of liquid in the strongly contracted foot is not a sufficient 

 evidence that they are the factors in producing the waves of loco- 

 motion, as similar isolated bodies of liquid are also found in the 

 musculature of the contracted mantle {Aplysia Plcurobranclicea). 

 . . . Simroth and Jordan missed the true explanation by not 

 taking into account the part played by the musculature of the 

 dorsal and lateral walls of body cavity." 



Carlson then describes a mode of locomotion, which he ob- 

 served only in Helix dupetithouarsi. Instead of the ordinary 

 locomotion by waves in the foot, this snail is able to lift up its 



1 Zeitsckr. Biolog , XL I., p. 196. 



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