Selectioti of Food in Stenior CcErideus (Ehr.) 95 



inconvenience or impossibility of swallowing as many as nine 

 Phacus at once. In very hungry Stentors six are sometimes 

 sw^allowed at one gulp, and once a S ten tor was observed to swal- 

 low seven, but in groups of more than seven some were always 

 rejected. 



So then in this experiment there are probably no mistakes in 

 discrimination whatever unless the rejection of a Trachelomonas 

 volvocina is considered a mistake. But the Trachelomonas was 

 in the resting stage and inactive, as were also the swarmspore 

 and the Coscinodiscus in Experiment 2. There is a possibility 

 therefore that the inactive particles are rejected and that only 

 moving, active particles (organisms), are ingested. To deter- 

 mine whether selection is made upon this basis, some Euglena 

 viridis were taken from a culture and killed in various ways, by 

 hea t, alcohol, acetic acid, etc. They were then thoroughly washed 

 and sucked up into capillary pipettes, those killed by heat in one 

 pipette, those killed by alcohol in another, and so on. Another 

 pipette was then filled with normal living Euglena?. Normal Sten- 

 tors were then isolated and fed with these F^uglenae in various con- 

 ditions in a mixed stream, precisely as was done with the various 

 substances in the preceding experim.ents. There was no discrim- 

 ination observed between any of the differently prepared Euglenae. 

 The dead Euglense were eaten with the same readiness as were the 

 living. Some Stentors rejected about equal numbers of each, 

 while others rejected all of both kinds. Similar experiments were 

 tried using Phacus and Trachelomonas as food, with the same 

 results. There was no selection between the living and the dead 

 organisms. 



Another possible way of explaining how the rejection of the 

 Trachelomonas, Coscinodiscus, and the swarmspore was made, is 

 that Stentor may be able to distinguish the different kinds of food 

 particles from each other, and that certain kinds of food may be 

 eaten with more readiness than others. This kind of selection 

 may, perhaps, take place under all conditions, or only under cer- 

 tain conditions. It may depend on the relative number of the 

 diff-erent kinds of particles, or the order in which they come. To 

 determine this matter a number of experiments were designed. 



