Selection of Food in Stentor Cceriileus (Ehr.) 125 



einen warmen Ort (von tiber 20° C.) vebrachte, trat eine Theilung 

 meistens sehr bald ein und die Tochterinfusorien begannen sofort 

 Karmin kornchen /u verschlucken." 



Metalnikow thus finds that although paramecia learn in some 

 way to refuse carmine after being fed with it for some time, yet as 

 soon as they divide, the daughter paramecia at once take up car- 

 mine as before. But he also says that after paramecia had been 

 left in carmine for 15 days or longer, most of them contained no 

 carmine whatever. Whether there were only very few paramecia 

 dividing in this latter case, or whether the paramecia after several 

 generations inherited this acquired character of refusing to ingest 

 carmine, we are not told. These important details as well as 

 others to which attention is called above, are not given in Metal- 

 nikow's paper, which is indeed only a preliminary paper. But 

 until such details are made known, and until Metalnikow 's 

 experiments are described in detail, so that they may be verified, 

 a discussion of our results which disagree in every essential par- 

 ticular, is futile. 



THE BASIS OF SELECTION 



A series of experiments will now be taken up which were 

 designed for the purpose of ascertaining if possible upon what 

 basis selection in Stentor is exercised. We have seen from the 

 experiments up to this point that Euglenae are eaten with more 

 readiness than Phacus, and that carmine is more readily eaten 

 than india ink, and that between living and dead organisms no 

 selection seems to be exercised. What can be the basis of discrim- 

 ination that gives such results.? So far as we can tell there are 

 only two possible methods by which Stentor can discriminate 

 between two different substances; one is by a chemical sense 

 ("tasting" and "smelling"), and the other by a tactual sense 

 ("touching"). Does Stentor select a particle by "touching" it, 

 or by "tasting it," or by both methods? (The psychological 

 terminology is used here merely for convenience. By tasting and 

 touching are meant reactions to chemicals and to contact and 

 form, respectively.) 



