THE PHYSIOLOGY OF LOCOMOTION IN GASTEROPODS. 139 



head and to push it forward ; it repeats the same movement with 

 the rest of its body, forming in this way two or three waves of 

 the whole body. It is unnecessary to continue the explanation 

 of this mode of locomotion : it is identical with the locomotion 

 in many worms and caterpillars. I say identical, because it is 

 immaterial how many waves there are. 



" Nevertheless," Carlson says, at the very end of his note, 

 " the peculiar mode of progression in the snail just described is 

 probably only an exaggerated form of the ordinary locomotion." 







I am sorry to be obliged to declare that Carlson did not know 

 or understand my publication at all. Therefore I must repeat 

 the passages in question, and I will try to translate them into 

 English, in order to prevent a second misunderstanding. 



Page 199 (/. c.) I say : The movement of the foot is formed by 

 waves. To understand this kind of movement we must im- 

 agine the sole divided into several parts (Fig. i). The wave 



begins through the extension 



| | | | | | | ; of the first division AB in the 



A B C D direction A, and by adhering 



FIG. i. to the ground at A. Then the 



same part contracts, so that B 



approaches A. At the same time BC leaves the ground, ex- 

 tends, until B adheres, then BC contracts, CD extends and C 

 adheres, etc. In this may we have waves advancing when 

 the foot is lifted from the ground from the anterior to the 

 posterior part of the body. (In Helix, Limax, etc., the waves 

 advance in the opposite direction.) All these waves must be 

 combined with appropriate adhesion in order to produce locomo- 

 tion in the posterior-anterior direction. 



The snail is able to change this mode of locomotion spon- 

 taneously, thus, for instance, Aplysia can execute movements similar 

 to caterpillars of geometridce (Spannerraupen). I think this expla- 

 nation should suffice, for this mode of locomotion is known (the 

 mode now described by Carlson for Helix). In part 3 of the intro- 

 duction of my work, page 200, I try to explain how extension 

 is possible. This, I think, is the only part that Carlson read ; 

 perhaps without understanding it. For in this chapter there is 

 almost no question of waves of locomotion. The whole snail as 



