Il6 Asa Arthur Schaeffer 



6 Yeast, Euglenae, Trachelomonas, and ink. Result: More 

 Euglenae and Trachelomonas than yeast. No ink. 



7 Ink. Result: Ink to the bulk of 3 Euglenae. 



8 Carmine. Result: Carmine to the bulk of 20 Euglenae. 

 10 Yeast, Euglenae, and Trachelomonas. Result: More Eu- 

 glenae and Trachelomonas then yeast. 



Only about half the Stentors of each dish were examined at the 

 end of an hour. The others were allowed to remain in the dishes 

 until next day. Examination then showed somewhat the same 

 results as are described above. In dish 4 however, no ink was 

 found in any of the Stentors, and in all the dishes in which ink and 

 carmine were placed the amount of these substances ingested by 

 the Stentors was less. The amount of yeast in the Stentors in 

 dishes 6 and 5 was also considerably less than on the previous 

 day. This decrease may have been due, in part at least, to the 

 torulas sinking to the bottom, notwithstanding the frequent stir- 

 rings to which the dishes were subjected. 



These experiments show that S ten tor can discriminate between 

 the torulas of yeast and the grains of ink or carmine, and that selec- 

 tion is more perfect for example, between yeast and ink than 

 between yeast and carmine They show also that less ink and car- 

 mine are eaten when food is present than when not. But in the 

 case of dish i the Stentors -are found to contain more carmine 

 when the yeast is also present than when only carmine is present 

 as in dish 8. I am unable to explain why this is so in this particu- 

 lar case. 



These two sets of experiments are probably sufficient to show 

 that Stentor can discriminate as well when enormous numbers of 

 particles touch the disk and pouch continuously for 24 hours, as 

 when a small number are swept into the pouch in rather slow suc- 

 cession, and that very minute particles of different sorts can be 

 sorted as accurately and rapidly as large particles. But all these 

 experiments were performed when the different particles were 

 mixed in about the same proportion. The question next came up: 

 What will happen when the proportions are changed ? Will Stentor 

 select food particles from particles that are not food as accurately 

 when the latter are greatly in excess.^ or in a mixture of different 



