Selection of Food in Stentor Cceruleus (Ehr.) II7 



kinds of food particles, will the ratio of ingesta vary directly with 

 the proportion of the amounts of the different particles as they 

 occur in the mixture? or does a variation in the different kinds of 

 particles, in the matter of proportion, have no effect upon the 

 amount of each kind ingested? 



Trachelomonas volvocina, T. hispida, Phacus longicaudus, P. 

 triqueter, Euglena viridis, and E. deses were placed in a small 

 preparation dish with about 10 cc. of filtered Stentor culture solu- 

 tion. About 100 times as much carmine as food organisms was 

 added and into this mixture several Stentors were placed, and the 

 dish set in the dark for about an hour. Examination at the end 

 of that time showed that about ten times as much food was eaten 

 as carmine. This is practically the same result that was obtained 

 in dish 3, described above, where the proportions of Euglena, 

 Trachelomonas, and carmine were equal. 



Another series of experiments bearing upon this point was per- 

 formed with mixtures of a species of Euglena and a colorless flagel- 

 late, probably a species of Chilomonas. The Euglenae were about 

 30/f long and about I2,« wide; Chilomonas, 18/^ long and 8/^ wide. 

 These two organisms were mixed in various proportions. Stentors 

 were then introduced and the dishes set in the dark for two hours. 

 The contents of the dishes, together wi h the results obtained, 

 follow : 



1 Mixture of Euglenae and Chilomonas in proportion of 4 : I. 

 Result: Ten times as many Euglenae ingested as Chilomonas. 



2 Chilomonas and Euglenae in proportion of 4 : i. Result: 

 Four times as many Euglenae mgested as Chilomonas. One 

 typical Stentor contained 200 Euglenae and 54 Chilomonas in 80 

 vacuoles. 



3 Chilomonas and Euglenae in same numbers. Result: About 

 six times as many Euglenae ingested as Chilomonas. 



4 Many Chilomonas. Result: Stentors contained as many 

 Chilomonas as Stentors in dish 6 contained Euglenae. 



5 Few Chilomonas. Result: Comparatively few Chilomonas 

 eaten. 



6 Many Euglenae. Result: Many Euglenae eaten, — from 

 5,000 to 11,000. 



