EFFECT OF LOW TEMPERATURES ON HYDRA. 51 



(The Hydra had been collected in a pond having a temperature 

 of 12° C.) When removed from the ice box both body and 

 tentacles were about one half contracted. The bud was about 

 the same size it was when the experiment was begun. Sections 

 showed body, tentacles and bud all with distinct cell structure, 

 Figs. 1-4. The minute changes in structure shown by these sec- 



FlG. I. Hydra after an exposure of nine days to a temperature of 2° C. ; B, 

 when taken from the ice box ; C, two minutes later, the Hydra now at the tempera- 

 ture of the room ; A, one minute later still ; the expanded Hydra had been stimu- 

 lated and rapidly contracted into this small mass. 



tions will be described in detail in a separate paragraph farther on. 

 Experiment j. — July, 1907. A brown Hydra, taken from a 

 pond having a temperature of 30 C. was kept at 4 for six days. 

 It gradually contracted and when removed appeared as drawn in 

 Text-fig. 2, A. The body was a spherical mass with tentacles 

 almost completely withdrawn. As the temperature was raised it 



