336 L- H. HYMAN AND A. W. BELLAMY. 



(galv.) to manubrium and margin. In Table IV. the potential 

 difference recorded between manubrium and subumbrella is that 

 between the distal border of the manubrium and a point on the 

 subumbrellar surface near the base of the manubrium ; the former 

 is negative (galv.) to the latter. Comparisons between margin 

 and subumbrella were taken on the middle of the subumbrellar 

 surface; in four cases (i, 4, 5, 10) the margin is negative, in four 

 cases (2, 3, 6, 7) the subumbrella is negative, due to the presence 

 of ripe gonads. In all cases tested in ^Eqitorca the exumbrella is 

 positive (galv.) to all other parts, and the margin is positive to 

 the manubrium. Mitrocoma shows the same relations as the other 

 medusae: manubrium negative to margin, subumbrella, and ex- 

 umbrella; margin negative to subumbrella; subumbrella negative 

 to exumbrella. 



3. Galvanotaxis. We were unable to find any definite galvano- 

 tactic response in the medusae noted above, except the general 

 tendency for the tentacles to direct themselves toward the cathode. 

 Probably the optimum strength of current was not found. Ban- 

 croft ('04) noted a precise response to the current in the medusa 

 Polyorclris. In this form the manubrium and tentacles were di- 

 rected toward the cathode, thus corresponding with the expectation 

 on the basis of our theory, as these parts of the animal are the 

 most positive (int.) regions. 



VI. CTENOPHORES. 



1. The Metabolic Gradient. The existence of a gradient along 

 the plate rows of ctenophores may be inferred from the fact that 

 the wave which passes along the plates originates usually at the 

 aboral pole and sweeps toward the oral pole. Child ('17) also 

 found a susceptibility gradient along the plate rows from the 

 aboral to the oral pole. This gradient, however, is readily re- 

 versible, at least temporarily. 



2. The Electrical Gradient. Tests were made by Hyman in 

 1920 on a small spherical ctenophore common at Friday Harbor, 

 which is probably Plcurobrachia ; a few specimens of Beroe were 

 also available. The data on PlcurobracJiia are given in Table V. 

 In 14 cases out of 20 the aboral pole was negative (galv.) to the 

 oral pole ; in 3 cases the oral pole was negative, and in 3 cases the 



