12 THE BIOLOGY OF STENTOR 



Phacus and Eiiglena recently killed by heat or alcohol were eaten 

 as readily as live ones. Stentor even discriminated between two 

 species of Phacus, predominately accepting triqueter and rejecting 

 longicaudus but there were no observations on whether the latter 

 was actually indigestible. 



In mass feedings from mixtures of equal parts, a stentor took in 

 1,500 Chlamydomonas, 85 Euglena, and 10 carmine particles. In 

 carmine alone 20 units were taken in. Hence generally less carmine 

 was eaten when food was present than when not, and carmine 

 was even rejected preferentially when much in excess over food 

 particles in the mixture. In India ink alone only 3 granules were 

 taken in, so the greater number of mistakes made with carmine as 

 compared with the smaller ink particles was the reverse of that 

 found with paramecia. These tests indicate that when fed, stentors 

 become more selective but they also rejected more of the favored 

 items as if no longer hungry. 



Conversely, hungry stentors were found to be less selective. 

 This may explain apparently contradictory observations, because 

 an investigator testing the ingestion of a given type of material 

 would be likely to use starved, clear stentors in which confusing 

 food vacuoles were not already present. Thus on occasion stentors 

 will ingest considerable numbers of fine carmine and ink particles 

 (Schuberg, 1890; Jennings, 1902). Before Schaeffer's studies, 

 Jennings had therefore concluded that there is no selection after 

 the material reaches the oral pouch, ''dissatisfaction" with the 

 meal resulting only in cessation of feeding and turning in a new 

 direction. Prowazek (1904) observed that coeruleus ate free-living 

 Chlorella though it could only partially digest them; and I have 

 found plentiful "food" vacuoles in samples of this stentor left 

 unnutrified for nearly a month and apparently re-feeding on waste 

 materials. Johnson (1893) remarked that coeruleus eats the alga 

 Scendesmus in quantity but apparently does not digest it and 

 quickly passes this material through the cell. Hence even when 

 indigestible materials are eaten, the animal can short-circuit to 

 the cytopyge food vacuoles with useless contents. 



On the evidence, food selection does occur in Stentor, though 

 by no means perfect and distinctly related in its acuity to the state 

 of the organism. 



The next consideration is the basis for this selection, and 



