140 A- J- Goldfarb 



13, 8,4 and 2. Greater irregularities took place in Experiments 6 

 and 7. In Experiment 6, 8 was the largest number of hydranths 

 present at one time during the first 5 days and during succeed- 

 ing 5 day intervals the largest number was 14, 17, 9, 10, 5, 13, 

 and 5 hydranths. In Experiment 7, the figures for the same in- 

 tervals were 10, 10, and 7 hydranths. 



In the second place, new hydranths were regenerated during a 

 longer cycle than either of the other two hydroids, 23 days in 

 Experiment 7, 26 days in Experiment 5, and 35 days in Experi- 

 ment 6, and would in all probability have continued to regenerate 

 for a longer period. After so protracted an interval the hydranths 

 were not only fewer as mentioned above but were decidedl/ 

 smaller or malformed. 



The most decided difference was observed in the behavior of 

 those stalks that were placed in the dark. From the first not a 

 single hydranth was regenerated from these stalks. Although 

 a little over one thousand branchlets and pedicels from various 

 colonies were placed in the dark, in no instance was a hydranth 

 produced. Pennaria unlike Tubularia and Eudendrium requires 

 no preliminary treatment in order to bring about a total cessation 

 of the regenerative processes. 



As might have been anticipated, the stalks in the dark required 

 particularly long exposures in order to stimulate the formation of 

 new hydranths. Exposures of 2 minutes and 5 minutes (Experi- 

 ment 5) proved totally inefficient. Exposures of 3, 5, 8, 10, 15, 

 20, 25, 30, and even 60 minutes (Experiment 6) were equally 

 inadequate, even though the exposures were made in the direct 

 rays of the sun. Exposures of 2 hours, 3 hours and 4 hours were 

 somet mes ineffective and sometimes produced hydranths. In 

 Experiment 6, for example, 200 pedicels exposed for 2 hours 

 regenerated during the next five days only 4 hydranths, while the 

 controls regenerated 70 hydranths in the same time. Exposures 

 of 3 and 4 hours gave no better results than the 2 hour exposures. 

 The hydranths so produced were frequently dwarfed. The mini- 

 mal time required to stimulate regeneration could be still further 

 reduced, in some colonies, by the simple expedient of exposing the 

 hydroids daily. Instead of two or more hour exposures, regenera- 



