THE EFFECT OF TEMPERATURE ON THE 

 REGENERATION OF HYDRA. 



FLORENCE PEEBLES. 



It has been shown that temperature has a marked effect on 

 the regeneration of Planaria torva. Lillie and Knowlton (2) 

 have proved by experiment that the optimum temperature at 

 which regeneration is completed is 29°. 7 C. ; the minimum, 

 about 3° C. 



During the last month I have made a series of experiments 

 on Hydra viridis and Hydra grisea, in order to test the effect 

 of temperature on the regeneration of the hypostome and 

 tentacles. A transverse cut was made through the reproduc- 

 tive zone of the polyp just posterior to the ring of tentacles. 

 The body thus deprived of hypostome and tentacles was sub- 

 jected to a gradual rise of temperature. The dishes in which 

 the Hydras were placed after the operation were partially sub- 

 merged in a water bath in which the temperature varied from 

 26° to 32° C. Readings were taken during the day at intervals 

 of four to six hours ; the variation was never greater than five 

 degrees. Control experiments were made at room temperature, 

 which ranged between 18° and 24° C. Observations were 

 made at intervals of twelve to twenty-four hours, and regen- 

 eration was considered complete when the new hypostome and 

 tentacles had attained their normal size. 



Normal Hydras were also placed in the water bath, in order 

 to determine what degree of warmth the uninjured polyps could 

 endure without apparent disturbance. In one series of experi- 

 ments the temperature was raised to 38° C, and as a result 

 not only the injured, but the normal, polyps died. At the end 

 of several hours they had completely disintegrated. 



That the rise of temperature up to 32° C. produces a marked 

 decrease in the time required for regenerating the lost parts is 

 seen in the following tables. In Table i the range of tem- 

 perature and the percentage regenerated at a given time are 



