330 



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



proceeds from the distal to the proximal ends of the tentacles, and 

 from the oral to the aboral end of the body of the hydranth; in 

 stems the gradient is likewise apico-basal. In the colony as a 

 whole and in each branch the susceptibility and reducing power 

 are, in general, highest in the terminal hydranths and decrease 

 basipetally among the hydranths and growing tips. In general, 

 then, metabolism is carried on more rapidly in the distal portions 

 of individuals, colonies, and branches and decreases basipetally. 



2. The Electrical Gradient. The electrical gradient of the hy- 

 droids was discovered by Mathews ('03) for Tubularia, Pennaria, 

 and Cauipanularia. He found that the distal portions are electro- 

 negative (galv.) to proximal portions. This result has been con- 

 firmed by us for the same and other genera and species. The 

 forms tested were: Tubularia- crocca, Pennaria tiarella, Obclia 

 geniculata, Obclia borealis, Eudcndriutn rainositni, and Schizo- 

 triclia (Plitiiiiilaria) tcnclla. The results are presented in Tables 

 II. and III. 



Tubularia crocca. -The data upon this species have been pub- 

 lished in another connection (Hyman, '20). Hydranths are nega- 

 tive (galv.) to stems, distal levels of the stem are negative to 

 proximal levels, except at the regions of branching, which are 

 usually negative'to levels immediately distal to them. 



Obclia geniculata. This species forms a small unbranched col- 

 ony, 1-2 cm. in height, consisting of a simple stem bearing lateral 

 hydranths alternately arranged, and growing by the formation of a 

 new bud at the apical end. In making the galvanometric tests the 

 entire colony was removed from the substratum and placed across 

 the electrodes. The electrical differences recorded in Table II., 

 therefore, concern the apical and basal regions of the colony; the 

 former is almost invariably negative (galv.) to the latter. 



Scliizotricha tcnclla. This species forms a delicate plume-like 

 branching colony, 3-5 cm. in length. Entire colonies were placed 

 across the electrodes ; the electrical differences recorded in Table II. 

 are, therefore, those between the apical and basal levels of the 

 colony; the former is negative (galv.) to the latter. 



Eudcndriuni rauiosuiii. The colonies of this species are large, 

 bushy, and much branched, with hydranths considerably larger 

 than those of the preceding two species. Most of the tests re- 



