THE AXIAL GRADIENTS IN HYDROZOA. 3/5 



Observations were made and the hydranths emerged recorded 

 every two to four hours during the daytime. No observations 

 were made during the night and hence there are in all of the 

 experiments gaps of from six to ten hours for each night period. 

 The first morning observation after such a gap is indicated in all 

 of the tables by an asterisk. 



There has been no selection of experiments for presentation in 

 this paper. Practically all of the experiments performed are 

 presented. 



2. Mass Experiments in June. These experiments were per- 

 formed between June 16 and July 9, 1919. The material was in 

 excellent condition up to July i, when the pieces for the last 

 experiment were cut. There was a great abundance of material, 

 growing rapidly and containing hydranths of all sizes. Material 

 was always cut on the same day as collected since, as is well 

 known, Tubularia will not keep in good condition in the labora- 

 tory in the summer. The hydranths fall off within twenty-four 

 fours, new ones being subsequently regenerated; further the 

 ccenosarc either dies away in the basal regions or else retreats 

 to other parts of the colonies. The regenerating pieces were kept 

 in the laboratory during the earlier experiments; the tempera- 

 ture was naturally variable and as recorded in the daytime 

 ranged from 15 to 24 C., with probably lower temperatures at 

 night. The later experiments were placed in the refrigerator at a 

 constant temperature of 13 C. 



The mass experiments performed in June are recorded in Table 

 III. As already stated, all of the apical halves were placed in 

 one finger bowl and all of the basal halves in another; the two 

 finger bowls were kept under the same conditions. At frequent 

 intervals the regenerating pieces were examined and the number 

 of oral hydranths emerged recorded. The record was taken 

 only when the hydranth had completely emerged from the top 

 of the ccenosarc and had spread its tentacles. 



Details of these experiments not given in the table are as 

 follows. Experiment I was performed on slender stems; experi- 

 ments 2 on stout stems; the other experiments were with medium 

 sized stems although there was some variation in the diameter 

 of the stems. Experiments I, 2, 5, and 10 regenerated in the 



