54 ARTHUR \V. GREELY. 



SUMMARY. 



1. In Hydra as well as Protozoa, a lowering of the tempera- 

 ture brings about certain definite structural changes that result in 

 the formation of an undifferentiated resting stage. 



2. The inhibition of cell division and reversal of vital phe- 

 nomena by a reduction of the temperature is shown in Hydra by 

 the fact that at a temperature of 6 C., the growth of a new bud 

 ceases, and the partially formed bud is gradually absorbed into 

 the body of the parent animal. 



3. A lowering of the temperature and an extraction of water 

 both bring about the same physical changes in the protoplasm 

 which serve to accelerate the development and metamorphosis of 

 the chrysalids of Cecropia. 



4. The absorption of water by the gastrocnemius muscle of 

 the frog in those salt solutions which, when used at dilutions 

 isotonic with its own substance, either have no chemical effect on 

 the muscle at the room temperature, or cause an increase in 

 weight, varies directly with the temperature, until the critical 

 point is reached at which the muscle proteids begin to coagulate. 

 In solutions of the same osmotic pressure, which cause the muscle 

 to lose water at the room temperature, this loss of water varies 

 directly with the temperature. Above the critical point of tem- 

 perature the muscles lose practically the same amount of water 



in all solutions, regardless of their initial effect on the muscle. 

 ZOOLOGICAL LABORATORY, 



WASHINGTON UNIVERSITY, March 18, 1903. 



