THE ZOOCHLORELL^E OF FRONTONIA LEUCAS. 



A collection in which the Frontonia showed innumerable zoo- 

 chlorellae had a pH value of 6.8. This culture remained in the 

 laboratory and a change from the original culture medium to 

 fresh spring water was made gradually. The hydrogen ion 

 concentration was taken every other day until the specimens 

 harbored few, and in some cases no zoochlorellae. Data thus 

 obtained are given in Table III. 



TABLE III. 



SHOWING VARIATIONS IN pH VALUE OF THE MEDIUM AS THE NUMBER OF 



ZOOCHLORELL^E DECREASED. 



June and July, 1926. 



DISCUSSION. 



An apparently significant fact observed during the course of 

 these experiments is: That Frontonia with abundant zoo- 

 chlorellae refuse to live in media of clear, fresh water. They 

 seem to require a stagnant, even putrid, medium containing 

 detritis, which serves as a place of hiding, much as do Spirostomum 

 ambiguum. Indeed these two protozoans have a common habitat 

 in every instance within the experience of the writer. But 

 Frontonia without zoochlorellse have been found in great abun- 

 dance in fresh running streams. 



It will be noticed from the foregoing investigations that a 

 host may experience either an increase or a decrease in the 

 number of its zoochlorellae, but that no statement is made 

 concerning their ability to regain them after having been com- 

 pletely freed. Regarding this subject we may say that repeated 

 efforts to induce Frontonia with no zoochlorellse to acquire them 

 were unsuccessful. Dangeard says of the zoochlorellae of Para- 

 mecium bursaria that they do not live long when freed in the 

 medium of their host. This suggested the possibility of inducing 

 Frontonia without zoochlorellae to appropriate them directly 

 from the body of a crushed specimen. Efforts to demonstrate 

 this, however, were unsuccessful. 



