Selectioti of Food in Stentor Cceruhiis {Ehr.) 107 



Perhaps the most significant difference of all between the ninth 

 and the tenth experiment is with regard to the occurrence of loops 

 in the paths of the organisms which were fed. These two experi- 

 ments are typical in this respect of nearly all the experiments 

 which form the basis for this paper. 



We find, first, that nearly all the loops occur in the paths of the 

 rejected particles. As it happens in these two experiments, no 

 particle is rejected without at least one loop m its path. Second, 

 when loops occur in the paths of ingested particles they are gener- 

 ally found only in those experiments where a comparatively large 

 proportion of the particles are ingested, or in other words, when 

 the Stentor is hungry or only in the first stages of satiety. Third, 

 in extensive experiments like the two preceding, more loops occur 

 in the first half of the experiments than in the last half, both in the 

 ingested and in the rejected particles. Fourth, very few loops 

 occur in feeding hungry Stentors. Fifth, very few loops occur in a 

 satiated Stentor. Sixth, the miaximum number of loops is found 

 when the Stentor is in the first stages of satietv. Seventh, in a 

 stream of mixed particles including food and bits of glass or sand, 

 the glass or sand is generally rejected with fewer loops than the 

 food particles. A conspicuous case of this is seen in the third 

 experiment. 



What is the real significance ot these loops? Are loops the 

 result of fatigue of the ingesting or of the rejecting mechanism, 

 or are they correlated with a certain physiologic state of Stentor 

 in such a way as to be a factor in the selection of food. ^ It appears 

 clear that the loops are not due to fatigue of the ingesting or re- 

 jecting mechanisms, nor of the apparatus for receiving the stimuli. 

 Fewer loops are made when the Stentor is satiated than when only 

 partial satiety sets in; this would not be the case if the occurrence 

 of loops were due to fatigue, as will presently appear. Further, 

 when excessively small particles are fed, such as the Euglenae in 

 the eighth experiment, as many as 11,000 may be eaten and several 

 times that number rejected, all within two or three hours, so that 

 fatigue could hardly occur from handling a few hundred as in 

 Experiments 9 and 10. Again we have seen that discrimination 

 is more precise as the Stentor becomes satiated. This shows that 



