44 



ARTHUR W. GREELY. 



turned to the temperature of the room. Thus a lowering of the 

 temperature seems to produce essentially the same effect on 

 Hydra as the contact stimulus on the Campanularian Hydroid in 

 Loeb's experiment. Likewise the structural changes appear to 

 be identical with those produced by the low temperature upon 

 the Protozoa. 



Hydra react to variations in the temperature in another way 

 which is interesting when compared to the reactions of Protozoa 



FIG. i. A budding Hydra after an exposure of twenty-four hours to a tempera 

 ture of 6C. The body is slightly shortened and thickened, and the absorption of 

 the ectoderm and entoderm cells has begun in the tips of the tentacles. 



under the same conditions. It has been a fact of common obser- 

 vation that the rate of cell division varies directly with the tem- 

 perature for all temperatures below the critical point. In my 

 experiments on Stcntor I showed that a lowering of the temper- 

 ature not only inhibits cell division but brings about the reverse 

 process. If a Stentor in the process of division be placed at a 



