REMOVAL OF GREEN BODIES OF HYDRA VIRIDIS. 295 



Lot A. May 10. Put 5 of the white hydras into spring water 

 without food. 



May 20. All alive and white. Four were on the lighted side 

 of the jar. 



May 27. Five hydras alive. Two showed no green color 

 but 3 had small green patches around the oral end. 



Lot B. May 10. Put 6 of the white hydras into spring water 

 without food. 



May 20. All alive and white. Three were on lighted side of 

 jar and 3 were on the bottom of the jar. 



May 27. Four hydras alive. One showed no green color 

 but 3 had small green patches around the oral end. 



The action of the glycerine upon the green hydra is to cause 

 the algal cells to leave the entoderm cells and to pass into the 

 digestive cavity, from which they are expelled to the outside 

 through the mouth when the hydra contracts. In many instances 

 when hydras were examined which had been in the glycerine solu- 

 tion for a few days, masses of the green algae could be seen in 

 their digestive cavities. In one case the expulsion of the algae 

 was actually seen. In other cases no masses of the algae were 

 ever seen. However, the bottom of the glass upon which the 

 animals were usually located always became more or less green 

 within a small radius of each individual, showing that the algae 

 were expelled and sank to the bottom of the dish. The algae 

 never increased to any noticeable extent, but apparently died. 



It seems evident from these experiments and observations that 

 the alga in Hydra viridis does not play a very important role in 

 the life processes. The animal is able to live many days in the 

 glycerine solution without food while in the process of losing its 

 algae. In Experiments IV. and X. the hydras were without food 

 for about 14 days, and in other experiments the animals have 

 appeared to be in a normal condition, except smaller in size, 

 when kept in glycerine solution without food for 21-30 days. 

 Experiments IV. and XIII. also show that hydras that have lost 

 all their green color can live at least for 7-17 days in spring 

 water without food and at the end of this time be in a normal 

 condition. Very likely they can live a much longer time than 

 this without food. 



