THE AXIAL GRADIENTS IN HYDROZOA. 



389 



Tubularia. This experiment shows that the metabolic gradient 

 of Tubularia is not a fixed and permanent gradient in the stem 

 but is readily variable under the conditions of the animal's 

 environment. Experiments such as those of Banus in which no 

 account is taken nor any description given of the conditions of 

 the material or the environment do not therefore merit serious 

 consideration. 



TABLE VII. 



RECORD OF MASS EXPERIMENTS WITH APICAL AND BASAL PIECES OF EQUAL 

 LENGTH, THE PIECES BEING TAKEN FROM MATERIAL KEPT ONE WEEK IN- 

 LABORATORY CONDITIONS BEFORE CUTTING. 



Temp. 13 C. Control, cxp. 21, Table III., in which the pieces were cut on 

 the same day as the material was collected. 



3. The Effect of the Presence of Branches. In the consideration 

 of the data on the electrical gradient in Tubularia it was pointed 

 out that the control of a Tubularia hydranth extends only for a 

 limited distance down the stem and that the stem beyond this 

 limit is more or less differentiated as another individual. This 

 differentiation, at first purely physiological, is later morpho- 

 logically apparent by the formation of a bud at the level of the 

 apical end of the new individual. The appearance of the bud 

 not only indicates the formation of a new individual but also 

 is an expression of a loss of control of the basal portions of the 

 stem by the original hydranth. It is therefore to be expected 

 that pieces taken above such lateral branches will have a lower 

 metabolic rate than pieces of the same level from unbranched 

 stems; and further that pieces taken below the branch, since 



