138 A. J. GoUfarb 



come to differ so radically from the controls. The latter by this 

 time were quite spent, i. e., they no longer produced hydranths 

 in the light. Those in the dark, likewise produced no more 

 hydranths but upon exposure to light not a single but a series of 

 hydranths were regenerated. In Experiment i, and 2, 4 and 5 

 hydranths, respectively, were regenerated in this manner. An 

 exposure of but 15 minutes sufficed to stimulate the production 

 of several hydranths. In this respect also Tubularia closely 

 resembles Eudendrium, though the latter was far more sensitive 

 to light, as shown by the larger number of hydranths regenerated 

 after exposures, by the longer regenerating period, and by the 

 briefer light stimulus that sufficed to bring these about. 



There are two minor points that may be mentioned at this 

 place, (i) Individual records made it quite certain that stalks 

 kept in the dark could regenerate a second and third time. (2) 

 Colonies whose stalks had been separated behaved in exactly the 

 same manner as those that were not so separated from the colony. 



The experiments were drawn to a close by the lateness of the 

 season, when good healthy stalks were no more to be procured. 

 It would have been interesting to have ascertained with far more 

 exactness the minimal exposure that would have stimulated a 

 regenerative cycle, to have ascertained whether a second or third 

 cycle could have been induced by such brief or briefer exposures. 



But the facts, so far as they go, clearly indicate that Tubularia 

 crocea behaves essentially like Eudendrium. During the first 

 cycle, regeneration takes place in the dark almost as well as in 

 the light; that after this period regeneration occurs only after the 

 stalks are exposed to the light. The two hydroids differ in that 

 longer exposures are required to stimulate Tubularia, and that 

 fewer hydranths result from such stimulation; in other words 

 Tubularia is less sensitive to light than Eudendrium. The uni- 

 formity of the results in the four experiments bespeaks the correct- 

 ness of these conclusions. 



