AUTOTOMY OF HYDRANTH OF TUBULARIA. iSl 



hydranths in jets of water which caused an incessant waving 

 of the hydranth on the stem. The hydranths were retained, 

 under such conditions, as long as was compatible with the tem- 

 perature and other external conditions. Abrasion was likewise 

 made the question of another set of experiments and here, too, 

 no effect could be correlated with the factor. With respect to 

 mechanical shock, when the stems are removed from the colonies, 

 data have already been given, for in the ice-chest experiments, 

 where the hydranths were retained for a long time, the stems 

 had been cut from the colony. Moreover, in those specimens 

 which were placed on floats in the sea and where the hydranths 

 did not fall off, the individuals had been cut from the stems. 

 Therefore, mere cutting of the stems is not a factor in autotomy. 



It will be seen that temperature seems to be the only consistent 

 factor involved in the decapitation. When the temperature is 

 kept at about 10 C. or 15 C, the hydranths are retained, re- 

 gardless of any other factors with the one exception of lack of 

 oxygen, which we believe to be inoperative except under wholly 

 artificial conditions. When it is recalled that in the sea, Tubularia 

 may be found throughout the summer 1 in latitudes where the 

 temperature of the water does not rise above 18 C. or 20 C., 

 while in lower latitudes- the occurrence of this species on the 

 piles and rocks is correlated with the times of the year, spring 

 and fall, when the water is cooler, we find sufficient data from 

 natural sources to conclude that temperature is die potent factor 

 in causing autotomy of the hydranths in colonies brought into 

 the laboratory. 



The case of Hydra, described by Greely 3 where the body be- 

 comes reduced to a mass of dissociated cells when the tempera- 

 ture is reduced to 4 C. and 6 C., seems to weigh against the 

 present conclusions, but more recently Caroline McGill 4 has 



1 As at South Harpswell, Maine, where the temperature of the water seldom 

 rises above 16 C. 



- E. g., Woods Hole, Mass. Tubularia disappears when the temperature 

 of the water reaches 20 C. It reappears again for a time in the fall. 



3 Greely, " Further Studies on the Effects of Variations of Temperature 

 on Animal Tissues," Scientific Papers. 



4 McGill, C., " The Effect of Low Temperature on Hydra," BIOL. BULL., 

 Vol. 14, 78. 



