Selection of Food ni Stentor Cceruleiis (Ehr.) 1 15 



of the quantity of substance taken in by the Stentors in the dishes 

 containing both food and carmine. There was variation among 

 different individuals in the amount taken, but none were entirely 

 devoid of carmine. 



A similar series of expermients m whicli mdia ink was substi- 

 tuted for carmine gave the same results, except that only about 

 half as much india ink was ingested as carmine. 



These experiments show that in an intimate mixture S ten tor 

 can discriminate and select with a high degree of accuracy such 

 minute food particles as Chlamydomonas from among indigestible 

 particles like carmine or india ink. In some cases the accuracy of 

 selection is almost perfect. Further, it is seen that the larger 

 amounts of carmine are eaten when no food is present, while little 

 or none is ingested when food is present also. 



In anothei experiment the Stentors came from a culture where 

 food was more abundant. Thev were fed with mixtures contain- 

 ing one or more of the following: veast, carmine, india ink, Eu- 

 glenae, Trachelomonas. Nine different combinations of these 

 materials were made in separate dishes. Equal quantities of the 

 different substances were employed in each experiment. At the 

 end of an hour the Stentors of each dish were examined as to the 

 materials ingested. The different combinations employed and 

 the results obtained are given in the following series. 



1 Mixture of yeast and carmine. Result: Stentors at the end 

 of an hour contained about twice as much yeast as carmine. The 

 total bulk ingested was equal to that of about 600 Euglenae. 



2 Yeast and mdia ink. Result: Less yeast ingested than in i. 

 Very little ink was eaten — about the bulk of three Euglenae. 



3 Euglenne, Trachelomonas, and carmine. Result: Many Eu- 

 glenae and Trachelomonas ingested. Carmine to the bulk of 

 about 15 Euglenae. 



4 Euglenae, Trachelomonas, and ink. Result: Same quantity 

 of Euglenae and Trachelomonas a in 3. Ink to the bulk of i 

 Euglena. 



5 Yeast, Euglenae, Trachelomonas, and carmine. Result: 

 More Euglenae and Trachelomonas then yeast. Carmine to the 

 bulk of 9 Euglenae. 



