614 SHEINA MARSHALL 



usual all through the cell and were not collected at the distal 

 end. On March 9 thirty-one Hydras were removed to 1-5 per 

 cent, glycerine. In the middle of April they were still quite 

 green. 



Several Hydras were kept in the dark for the same purpose, 

 but although the colour grew somewhat paler they all died 

 before the green cells had been entirely lost. Hadzi (5) has 

 also noted that they do not survive in darkness. Eggs, 

 apparently colourless, which were produced in the dark, died 

 before hatching. 



Some brown Hydras were induced to swallow pieces of 

 H. viridis by slipping the latter inside the carapace of 

 Daphnia, but they were ejected along with the remains of 

 the food and had no effect. 



Daphnia were also fed on a pure culture of Chloro- 

 sphaera and were then given to the Hydras, but with no 

 effect. 



There have been many attempts to make a pure culture of 

 the green organism inhabiting H , v i r i d i s . In Beyerinck's (1) 

 paper on the culture of algae and lichens he states that he has 

 been unable to obtain a pure culture of the zoochlorella from 

 Hydra, but he adds a foot-note to the effect that he had 

 obtained such a culture, and that the organism was indistin- 

 guishable from Chlorella vulgaris. 



Later writers have made damp cell-cultures and have seen 

 division taking place, but so far as I know there has been no 

 large culture obtained. 



I washed H. viridis in several changes of sterile water 

 and then teased it up with needles till practically all the green 

 cells were freed. They were then sown on Miguel solution in 

 tubes and sporulation dishes, on Amoeba-agar, and on agar 

 made up with Miguel solution, but in none of these was any 

 culture obtained. 



In one tube of Miguel, Chlorosphaera limicola 

 (Beyerinck) appeared. The Daphnia on which the Hydras 

 were fed were themselves fed on a mixed green culture which 

 proved to contain Chlorosphaera, and the organism may 



