292 D. D. WHITNEY. 



Various theories have been advanced to account for the pres- 

 ence and function of this green alga in animal cells. Some 

 workers have maintained that these cells assimilate the C0 2 

 which is given off by the animal cells, and then in their turn give 

 off oxygen which is used in the life processes of the animal cells. 

 Others have imagined that the algae might manufacture products 

 in the presence of sunlight which are passed out into the animal 

 cells and used by them as a food. 



Instead of a translocation of the algal reserves to the animal 

 tissues Famintzin and Beyerinck have shown that the alga itself 

 is liable to absorption and digestion by the host. Gamble and 

 Keeble found that mature and immature Convoluta roscoffensis 

 digest masses of their own green cells and that the animals ob- 

 tain little if any food by the translocation of the reserves of its 

 green cells. 



They also found that the alga is not transmitted through the 

 egg to the following generation as in the case of Hydra viridis, 

 but that the young embryos of each generation are infected by 

 the alga as soon as they leave the egg. Furthermore, " the re- 

 lation between animal and green cells is a complex one, and can- 

 not be described as symbiotic. The green cell once in the body 

 of the animal probably never escapes ; either it is digested or it 

 dies when the animal dies." 



In the winter of 1905-6 while keeping Hydra viridis in vari- 

 ous chemical solutions in order to find some means of causing the 

 development of the reproductive organs it was discovered that 

 animals kept in a weak solution of glycerine lose their green 

 color. 



A series of experiments was carried on at that time and in the 

 following winter .and spring under the direction of Prof. T. H. 

 Morgan and Prof. W. J. Gies. The following data will show 

 the nature of the results obtained : 



Experiment I. — February 19, 1906. Temperature 20°C. 

 Several green hydras were put into a 1.25 per cent, solution of 

 glycerine without food. 



February 26. Only 3 were alive, and appeared white to the 

 ordinary eye. These were placed in spring water without food. 



March 3. The 3 hydras were beginning to become green in 

 color at the oral end. 



