EFFECT OF TEMPERATURE ON ANIMAL TISSUES. 



45 



temperature of 4C. a fusion of the partially divided halves takes 

 place. Among Hydra the formation of buds, which finally 

 become distinct individuals, may be considered analogous to the 

 process of cell division among Protozoa. It was found that if a 

 Hydra in the earlier stages of the process of budding be placed 



FIG. 2. The same Hydra as in Fig. I, after an exposure of six days to a tem- 

 perature of 6C. The absorption of the tentacles and bud is nearly complete. 



at a temperature of 4C., not only does the growth of the bud 

 stop instantly, but an absorption of the bud into the body of the 

 parent commences, and continues until all traces of the bud have 

 disappeared. (See Figs. I and 2.) In order to demonstrate 

 this absorption of the bud, great care is needed in lowering the 



FIG. 4. FIG. 3. 



FIG. 3. The final resting stage of Hydra, formed after an exposure of four to 

 seven days to a temperature of 6C. The body consists of an undifferentiated mass of 

 protoplasm. 



FIG. 4. The tip of a tentacle of a Hydra that has been exposed to a tempera- 

 ture of 6C. for twenty-four hours, showing the dissolution of the octoderm and 

 endoderm cells. 



temperature. If the temperature is quickly reduced to iC. the 

 Hydra go to pieces, but if the temperature be maintained at from 

 4 to 6C., and is not suddenly varied in either direction, the 

 process of absorption can be easily seen. Six or seven days are 

 required for the complete disappearance of the bud. These two 

 experiments seem to show that among the Ccelenterates as well 



