144 DYNAMICS OF LIVING MATTER 



occurs the cilia on both sides of the body, with the exception of a 

 small number on the anode side, point forward, and the animal is 

 therefore pushed backward to the anode. 



Maxwell and I have investigated a little more carefully the reactions 

 of a Crustacean, Palamonetes, to a constant current.* When these 

 animals are put into a trough through which a current passes (whose 

 intensity is neither too weak nor too strong), all the animals move 

 gradually toward the anode. The Crustacean can swim forward 

 or backward and can walk forward, sidewise, or backward. The 

 effect of the current does not in this case consist in a compulsory orien- 

 tation of the organism, but merely in a compulsory change in the rela- 

 tive position of the legs, or swimmerets. The result is always such as 

 to facihtate the motion to the anode, and to render more difficult the 

 locomotion to the cathode. " Palamonetes uses the third, fourth, and 

 fifth pairs of legs for its locomotion. The third pair pulls in the for- 

 ward movement, and the fifth pair pushes. The fourth pair generally 

 acts like the fifth, and requires no further attention. If a current be 

 sent through the animal longitudinally, from head to tail, and the 

 strength be increased gradually, a change soon takes place in the posi- 

 tion of the legs. In the third pair the tension of the flexors predomi- 

 nates, in the fifth the tension of the extensors. The animal can 

 thus move easily with the pulling of the third and the pushing of the 

 fifth pairs of legs, that is to say, the current changes the tension of 

 the muscles in such a way that the forward motion is rendered easy, the 

 backward difficult. Hence it can easily go toward the anode, but only 

 with difficulty toward the cathode. If a current be sent through the 

 animal in the opposite direction, namely, from tail to head, the 

 third pair of legs is extended, the fifth pair bent ; that is, the third pair 

 can push, and the fifth pair pull. The animal will thus go backward 

 easily and forward with .difficulty. When Palamonetes swims for- 

 ward, the swimming appendages, among which the tail fin must be 

 counted, push backward forcibly and forward gently; in swimming 

 backward the opposite occurs. If the current be sent through Pala- 

 monetes in the direction from head to tail, the swimming appendages 

 and the tail also are stretched backward, or dorsad, to their fullest 

 extent. This proves that the tension of the muscles that move those 

 organs backward is greater than that of their antagonists. The shrimp 

 can thus swim forward toward the anode easily under the influence 

 of such a current, but backward only with difficulty. If the current 

 passes through in the opposite direction, from tail to head, the tail and 

 the ventral appendages are turned forward. The tension and the 



* Loeb and Maxwell, Pfliiger's Archiv, Vol. 63, 1896. 



