42 



TROPISMS 



4- 



If a meridional strip passing from the edge on one side through 

 the center of the bell to the other edge be prepared and the current 

 passed through transversely, tentacles and manubrium turn and point 

 toward the cathode (Fig. 12). A reversal of the current initiates a 

 turning of these organs in the opposite direction, which is usually com- 

 pleted in a few seconds. This can be repeated many times and the 

 tentacles continue to respond after hours of activity. The manubrium, 



however, tires sooner and fails to re- 

 spond. If the strip is placed with its 

 subumbrella surface upward and ex- 

 tended in a straight line parallel to the 

 current lines, the making of the current 

 causes the tentacles at the anode end 

 to turn through an angle of 180° and 

 point toward the cathode. The ten- 

 tacles at the cathode end become more 

 crowded together, reminding one of the 

 tip of a moistened paint brush, and 

 also point more directly toward the 

 cathode (Fig. 13). The experiment 

 may be varied in still other ways by 

 cutting smaller or larger pieces from the edge of the swimming bell, 

 but the response is always the same. The tentacles, wherever pos- 

 sible, and to a less extent the manubrium, bend so as to point 

 toward the cathode. The response depends in no way upon the con- 

 nection of these organs with the swimming bell, muscles, or nerve 

 ring, for it is obtained equally well with isolated tentacles and 

 pieces of tentacles. Isolated tentacles when placed transversely to 



Fia. 12. — Tentacles T and manu- 

 brium M of a jellyfish (Polyorchis) 

 under influence of galvanic current 

 are turned to the negative pole. 

 (After Bancroft.) 



-1- 



^^ 



Fio. 13. — Strip of jellyfish showing that under the influence of galvanic current tentacles 

 on both ends point towards cathode. (After Bancroft.) 



the current lines curve so as to assume a more or less complete 

 U-shape, with their concave side toward the cathode. When placed 

 parallel to the current, the tentacles do not curve." 



The latter observation shows the fact that the whole 

 reaction is due merely to an increase in the tension of 

 the muscles on the cathode side of the organ. 



Phenomena of g-alvanotropism can be observed also 

 in infusorians. Thus Verworn 493 observed that when 



