37 8 LIBBIE H. HYMAN. 



in spite of diligent search by the collectors. It was, however, 

 obtainable early in December in fair abundance, and experiments 

 were performed upon it from December 6 to 16. The colonies 

 at this time were in excellent condition, branching freely and 

 growing rapidly. The general appearance of the material was 

 much the same as in June except that the hydranths attained a 

 larger size than in June and a few lots of material consisted of 

 very long stems, much longer than any observed in June. The 

 majority of the December material, however, was branching so 

 freely that most of the stems were relatively short and in some 

 cases it was necessary to cut pieces less than 8 mm. long. The 

 temperature of the running water in the laboratory in December 

 was 8 C. and it was therefore possible to keep the material for 

 two or three days in excellent condition. Two collections of 

 material were used in the December experiments; one collected 

 on December 6 was cut for experiments on December 6, 7, and 8; 

 the other, collected on December 8, was used on December 8 

 to 1 1 . All of the pieces were kept on the water tables in slowly 

 running water at a temperature of approximately 12 C., varying, 

 however, for slight periods from 10 to 14. 



The results of the mass experiments performed in December 

 are given in Table IV. In experiment 26, the pieces were about 

 5 mm. long; in experiment 27, 5-8 mm. long; and in experi- 

 ments 35, 44, and 47, 1012 mm. long. The pieces were cut 

 as in Fig. I, except in the case of experiment 44, in which the 

 basal pieces were cut at the proximal end of long stems so that 

 some 10-15 mm. of stem was removed between the levels of the 

 apical and basal pieces in this experiment. There was no 

 mortality among the pieces. The temperature throughout was 

 12 C. 2. 



4. Conclusions from Mass Experiments. The data given in 

 Tables III. and IV. permit us to draw the following conclusions 

 concerning the rate of regeneration of oral hydranths on apical 

 and basal pieces of the stem of Tubularia of equal length : 



(a) Hydranths invariably emerge first on the apical pieces 

 and a considerable number of such pieces will have regenerated 

 before any of the basal pieces have produced a hydranth. 



(b} At any given time there are in nearly all cases a greater 



