Selection of Food ui Stentor Cceruleiis (Ehr.) 



103 



TABLE Villa 



Tabulation of Results of Experiment 8 



As this table shows, the percentage of Euglena eaten decreases 

 steadily throughout the experiment, from 86 per cent to 40 per 

 cent; while that for Trachelomonas decreases from 66§ per cent 

 to o. The percentage of Euglena rejected increases from 14 per 

 cent to 60 per cent; of Trachelomonas from 3:5 per cent to 100 per 

 cent. Similar changes were found in all the experiments of like 

 character with Stentor, including a number which I do not publish 

 in detail. It is evident that this regular change cannot be due 

 to chance variations in the food, but must be due to an alteration 

 in the physiologic state of Stentor itself. In some way the Sten- 

 tor changes as it takes food, so that stronger and stronger stimuli 

 are required to set off the ingesting mechanism. Such a change 

 is of course parallel with what we observe in higher organisms. 



We find therefore that we have in this unicellular organism 

 physiologic conditions corresponding to what we call hunger and 

 satietv in higher forms. Differences in behavior due to hunger 

 and satiety have not heretofore been demonstrated for those pro- 

 tozoa that secure their food by means of an alimentary vortex. 

 The experiments we have just described, primarilv designed to 

 test the power of selection, indicate strongly the existence of such 

 differences. Let us now turn to experiments that were planned 

 to test this matter. We wish to determine what differences exist 

 between hungry and satiated Stentors, and whether there are inter- 

 mediate conditions, manifesting themselves in differences in be- 

 havior. 



