82 C. L. HOOD. 



collection was set aside and remained untouched until August I . 

 On this date the zoochlorellae in twelve specimens examined were 

 innumerable (Fig. 3). 



On June 8, 1926, eight cultures, containing twelve specimens 

 per culture, of Frontonia harboring relatively few zoochlorellae, 

 were started in fresh water to which a small amount of detritis 



FIG. 3. Showing increase of zoochlorellae in Frontonia after the same collection 

 (Fig. 2) had remained in the laboratory for thirty days. 



from the collecting dish was added. These cultures remained in 

 the laboratory with abundant light, but never in direct sunlight, 

 until July 8, without adding more fresh spring water. At this 

 time slides were made from each culture. The zoochlorellae in 

 95 per cent, of the animals were innumerable. Checks which 

 corroborate these findings were made with cultures started June 

 10 and 12. 



From these results the conclusion, that the number of zoo- 

 chlorellae in Frontonia leucas may be increased by an increase 

 in stagnation and putrefaction of the medium in which they 

 live, seems logical. 



INFLUENCE OF OSMOTIC PRESSURE. 



In an effort to explain, beyond the simple statement of the 

 difference between stagnant and fresh water, these variations in 

 the number of zoochlorellae inhabiting each host, cultures with 

 various osmotic pressures were made as follows: Three cultures 

 using distilled water, three cultures using fresh spring water, 

 three cultures of one per cent, dextrose in spring water. Into 

 each of these cultures were placed six specimens in which the 

 zoochlorellae were numerous, and six with no zoochlorellae. It 

 was found that upon being put into distilled water the organisms 

 with zoochlorellae promptly disintegrated. Ejection of zoo- 



