Selection of Food in Stentor Cceruleus (Ehr.) 



lOI 



Experiment S. Discrimination between Organisms of Similar 



Size and Shape 



As a final test m food discrimination in which the path and fate 

 of each particle was recorded the following experiment was de- 

 signed and performed. Two kinds of organisms were used, one 

 being Trachelomonas volvocina and the other a species of Euglena 

 which upon very slignt disturbance contracted into a spherical 

 mass of almost exactly the same size as that of a Trachelomonas. 

 The organisms were fed from a capillary pipette in a mixed stream, 

 the number of Eugleme and Trachelom-onas being as nearly equal 

 as possible. The loops were not recorded. The results follow: 



e = Euglena; t = Trachelomonas; th = Trachelomonas hispida 



TABLE \Tn 



Experiment 8. Discrimination between Organisms of Similar Size and Shape 



EATEN REJECTED EATEN I REJECTED 



4e 



626 



Ot the 62 organisms 32 were f-uglenae, 29 Tracheolmonas vol- 

 vocina, and I T. hispida. Seventeen Euglenae were eaten and 15 

 rejected; and of the Trachelomonas 3 were eaten and 27 rejected. 

 That the Euglenae were eaten with more readiness than the Tra- 

 chelomonas is evident from an inspectoin of these figures, which 



