THE AXIAL GRADIENTS IN HYDROZOA. 395 



12 C. 2. It will be observed that in the case of the mass 

 experiments, the basal pieces on the whole regenerate more 

 rapidly than the apical pieces, although both are retarded as 

 compared with the controls. The individual experiments bring 

 out the same point. The number of deaths was considerable 

 but of 39 pairs in which both pieces regenerated, the basal pieces 

 preceded the apical pieces in 14 cases, or 38 per cent, as compared 

 with the result under normal conditions as given in Table V., 

 where but 8 per cent, of the basal pieces precede the apical pieces. 

 A number of interesting points are brought out by these experi- 

 ments with ether and cyanide. In the first place the rate of 

 regeneration is greatly retarded. In the case of cyanide, where 

 different concentrations were employed, the retardation is pro- 

 portional to the concentration used. This retardation is evi- 

 denced by both kinds of pieces, the apical pieces being, however, 

 more retarded than the basal pieces, with the consequence that 

 the usual relation between the time of regeneration of apical and 

 basal pieces is reversed. Now there can be little doubt that the 

 rate of regeneration of pieces of Tubularia primarily depends 

 upon the rate of chemical processes in those pieces. The effect 

 of temperature upon the rate of regeneration is sufficient proof 

 of this. Therefore, since depressing agents retard the rate of 

 regeneration, it is impossible to doubt that they bring about this 

 effect by lowering the rate of chemical reactions in the pieces. 

 This is further evidenced by the fact that concentrations of these 

 reagents which are effective at room temperatures are entirely 

 without effect at temperatures of 12 and 13 C. Thus I per 

 cent, ether is very effective at 20 C. but has no effect at 12 C. 

 In order to alter the relations of apical and basal pieces at 12 C., 

 it is necessary to use 2 per cent, ether. The same is true of 

 cyanide. When, therefore, the metabolic rate is already lowered 

 by low temperature, the action of depressing agents is diminished. 

 This further supports the statement made at the beginning of 

 this section that the action of depressing agents is related to the 

 rate of chemical activity of the protoplasm which is exposed to 

 them, and that such effects are greater the higher the metabolic 

 rate of the living material. The differential effect, therefore, of 

 ether and cyanide on the rate of regeneration of apical and basal 



