EFFECT OF LOW TEMPERATURES ON HYDRA. 83 



in only a few places showed cell boundaries. The body was in 

 the main a mass of protoplasm with degenerating nuclei scattered 

 through it, that is a syncytium. The nuclei were small and 

 pycnotic, showing direct evidence of degeneration. 



From the above experiments it will be seen that the changes 

 which take place in Hydra when subjected to low temperatures, 

 are somewhat variable. Those collected in summer, when the 

 water in which they have been living is warm react differently 

 from those collected in winter when the water is cold. In Hydra 

 from cold ponds (temperature 8° to 12° C.) lowering the tem- 

 perature to 2° and keeping it there for as long as two weeks has 

 little effect except to cause contraction for the time being. As 

 soon as the temperature is raised, they assume their ordinary 

 expanded form. Usually the tentacles are slightly altered. They 

 become opaque at the tips and cannot expand as far as before 

 exposure to cold. Hydra that are budding show no absorption 

 of the bud such as described by Greely. As soon as such Hydra 

 are placed at room temperature the buds, as well as the parent 

 body, become actively contractile. 



Hydra collected in summer when the pond water is warm show 

 more marked effects when the temperature is reduced. They 

 contract into small masses and when brought, after several days 

 exposure to cold, into water the temperature of the room, do 

 not immediately expand to their normal length. Even in 

 summer Hydra I have never observed absorption of the buds 

 except in cases where there was distinct degeneration, due to 

 some other condition than low temperature. Both summer and 

 winter Hydra, when the temperature is reduced, lose in volume. 

 This loss is more pronounced in the summer than in the winter 

 Hydra. 



The cytological changes brought about by low temperatures 

 are interesting. They are in the main such as can be ascribed 

 to loss of water. When more marked changes take place they 

 are always accompanied by distinct evidences of degeneration. 

 The temperature effects are always much more pronounced in 

 Hydra collected in summer than those collected in winter. Fig. 

 6 is drawn from the endoderm of a winter Hydra which had been 

 kept at a temperature of 2° C. for nine days. The structure is 



