GALVANOTROPISM 



35 



the extensors, and since it is antagonized by the tension 

 of the flexors, the animal can swim forward but not 

 backward, or only with difficulty; if we put the animal 

 with its head toward the cathode the tail is bent ventrally 

 (Fig. 3), which means that the tension of the flexors is 

 stronger than that of the extensors. As a consequence 

 the animal can swim backward but not forward, or onlv 



Fig. 3. — Forced position of shrimp when positive current goes from tail to head. 

 Tension of flexors of tail fin prevails over that of extensors. Animal can swim backward 

 (to anode), but not forward. (After Loeb and Maxwell.) 



with difficulty. In both cases the result will be a swim- 

 ming of the animal to the anode, in the former case by 

 swimming forward in the latter by swimming backward. 

 We can further show that the tension of the muscles 

 of the legs of Palcemonetes is always altered in such a 

 sense by the galvanic current that motion toward the 

 anode is facilitated, while that toward the cathode is 

 rendered difficult or impossible. The animal uses the 

 third, fourth, and fifth pair of legs for its locomotion 

 (Fig. 2). The third pair pulls in the forward movement 



