Selection of Food in Stentor Cceruleiis (Ehr.) 85 



ing. It may go down to the mouth and be nevertheless finally 

 rejected, or it may go only halfway down before its direction is 

 reversed. And further, the particle may travel back and forth 

 many times in the funnel, or in the pouch, or through the extent of 

 both, before either ingestion or rejection takes place. For the 

 sake of shortening the description in the subsequent experiments 

 this traveling back and forth of a particle will be described as the 

 forming of "loops" in its path, each reversal from the ultimate 

 direction (as determined by the fate of the particle) being con- 

 sidered as one loop. Such loops in the path of a particle in the 

 funnel often take place while another particle in the pouch is either 

 rejected or passed on into the funnel. These two sets of cilia may 

 therefore beat quite independently of each other. 



Other methods of rejecting or getting rid of substances are also 

 frequently employed especially when there are large numbers of 

 objectionable particles impinging on the Stentor's disk, as clouds 

 of carmine or other indigestible material. In addition to a rever- 

 sal of the membranellre, bending away, contraction, and breaking 

 of the foothold and swimming away, which reactions have been 

 described by Jennings ('02) there are several other methods of 

 reacting toward large quantities of indigestible particles which 

 have not heretofore been described. Some Stentors close up the 

 rim of the pouch almost completely for longer or shorter periods 

 when surrounded by dense clouds of carmine. This method of 

 preventing the ingestion of particles of carmine is most frequently 

 observed after the Stentor has torn away from its foothold and is 

 swimming freely in the water. This method is undoubtedly 

 effective but for some reason the reaction is not persisted in for 

 any length of time. Another and much more interesting modi- 

 fication of behavior occurs also under conditions similar to those 

 which induce closure of the pouch, but it is observed in Stentors 

 which have become attached again though still surrounded by 

 dense clouds of carmine. Stentors under these circumstances are 

 not quite as fully extended as when carmine is absent, but all the 

 groups of cilia function as usual except with this interesting modi- 

 fication at times. The discal cilia instead of carrying the particles 

 on toward the pouch as they strike the disk, roll the particles 



