Selection oj Food in Stentor Cccruleus iEhr.) II9 



but they are rarely captured, though they frequently come in con- 

 tact with the Stentors. Five dishes contained equal amounts of 

 tap water and carmine particles; into some of these there was 

 introduced also certain quantities of food particles, in others none. 

 Fifty Stentors were placed in each of these dishes, and then were 

 examined after 20 minutes. to determine the relative amounts of 

 carmine taken. The conditions and results are as follows. 



1 Carmine alone. At the end of 20 minutes the Stentors con- 

 tained carmine to the bulk of about 400 Euglen?e. 



2 Several thousand paramecia plus carmine. 



3 Several hundred paramecia plus carmine. 



In dishes 2 and 3 none of the Stentors contained any paramecia. 

 Their carmine content was about half that of the Stentors of dish i, 

 a bulk equivalent to that of about 200 Euglen.'e. 



4 Trachelomonas hispida, T. volvocina, and carmine. The 

 Stentors contained a very few specimens of Trachelomonas. Car- 

 mine to the bulk of about 80 Euglenae. 



5 P^uglena viridis and carmine. The Stentors had in 20 

 minutes taken each about 275 Euglenae, and carmine equivalent 

 in bulk to about 4 Euglenae. 



These results seem to indicate that the presence of the paramecia 

 in dishes 2 and 3 decreased the amount of carmine taken up by 

 the Stentors. The paramecia frequently touched the disk, and 

 were often swept into the Stentors' pouches but always escaped, 

 and it is probable that this touching of the discal or pouch cilia by 

 the paramecia altered the physiologic condition of the Stentor in 

 much the same w^ay as if several paramecia had been eaten. It 

 might be thought that the bacteria carried over with the paramecia 

 produced the result described above, but this is probably not the 

 case, since in many experiments of this nature carmine was put 

 into a portion of filtered paramecia or Stentor culture solution 

 which was full of bacteria, and yet the maximum quantity of car- 

 mine was taken up. 



The evidence thus indicates that it is only necessary for food 

 particles to touch the Stentor's disk or pouch in order that Stentor 

 should then to some extent reject the waste particles. 



A question related to the one we have just considered is the fol- 



