128 PEEBLES. 



The change in appearance of the injured region was so slight 

 from day to day that observations were less frequent than in 

 the experiments where the temperature was higher. It will be 

 seen from Table 6 that by a lowering of the temperature a 

 delay of twenty-four to ninety-six hours results in the process 

 of regeneration. On the other hand, an increase of tempera- 

 ture brings about an increase in rapidity of the rate of regen- 

 eration of twenty-four to forty-eight hours for Hydra grisea, 

 and also a slight increase for Hydra viridis. 



While making these experiments with temperature, I tried 

 the effect of colored lights upon the regeneration of Hydra. 

 Four colors were tested — red, blue, green, and yellow. These 

 colors were obtained by making solutions of congo red, copper 

 sulphate, anilin green, and potassium bichromate, respectively. 

 These were tested with the spectroscope and found nearly 

 monochromatic. 



A number of experiments were made and also control experi- 

 ments in darkness and in diffuse daylight, but the process of 

 regeneration was in no way influenced by any of the colors. 



The experiments noted here were made in the Physiological 

 Laboratory of Bryn Mawr College, and were directed by Dr. 

 J. W. Warren, to whom I wish to express my thanks for sug- 

 gestions and assistance. 



Bryn Mawr, Pa., 



June, 1898. 



REFERENCES. 



Davenport, C. B. Experimental Morphology. 1897. 



LiLLiE AND Knowlton. On the Effect of Temperature on the 



Developmexit of Animals. Zoological Bulletin. Vol. i, No. 4. 



1897. 

 Peebles, F. Experimental Studies on Hydra. Arch. f. Entiu. d. 



Organismen. 5. Band, 4. Heft. 1897. 

 Wilson, E. B. The Heliotropism of Hydra. Amer. Nat. Vol. xxv. 



1891. 



