BEHAVIOR OF CCELENTERATA 



209 



the anode side just below the base of the tentacles. As a result of the 

 contraction on the anode side, the Hydra bends toward the anode. As 

 soon as it comes into a position with the anterior end directed toward 

 the anode, the entire body contracts, since a Hydra in this position is 

 stimulated more than in any other (Fig. 128, 5). In a stronger current 

 the complete contraction takes place first, then the animal slowly bends 

 over toward the anode. If, as sometimes happens, the foot is free while 

 the head is attached, the bending takes place as usual on the anode side. 



Fig. 129. — Successive stages in the reaction of a Hydra to the electric current when the 

 foot is unattached. The foot becomes directed toward the anode. After Pearl (1901). 



The result is necessarily that the foot becomes directed toward the anode, 

 so that in this case the orientation of the animal is the reverse of that 

 found in the specimens attached by the foot (Fig. 129). This result 

 shows clearly that the orientation to the electiric current is due to the 

 direct local contractions caused by the current on the anode side, and 

 is not due to an attempt on the part of the animal by anything like a 

 process of trial to come into a certain definite position. 



In a Hydra placed transversely to the current, the tentacles con- 

 tract in a peculiar way. A weak current causes only the tentacles which 

 are in line with the current to contract, and of these, that extending 

 ix)ward the cathode contracts more quickly and more completely than 





r^== 



Fig. 130. — Effects of the consta,nt electric current on pieces of Polyorchis. After Bancroft 

 (1904). A, meridional strip passing through the manubrium. B, similar strip stretched out 

 in line with the current. C, isolated tentacles. 



that directed toward the anode (Fig. 128, a). If the Hydra is lying 

 parallel with the current, the body contracts much more readily when 

 the anterior end is directed toward the anode than when it is directed 

 toward the cathode. In either of these positions the tentacles usually 

 remain extended, and somewhat incHned toward the cathode (Figs. 128 

 and 129). But if a very strong current is used, both body and ten- 



