114 J- PAUL VISSCHER. 



The feeding reactions of animals have long been a favorite study 

 for students of animal behavior. More recently the reactions of 

 certain protozoa have been intensively studied with the hope that 

 such problems as the choice of food would be reduced to their 

 simplest terms in these unicellular animals which in other respects 

 apparently stand near the bottom of the scale of development. 



Ehrenberg ('38) was undoubtedly one of the first to make ob- 

 servations on the ability of protozoa to choose their food. He 

 records experiments on the ingestion of carmine by various organ- 

 isms in an attempt to show that protozoa do not select their food. 

 Entz ('88) and others of his time were, however, strong in their 

 contention that infusoria are able to select their food, ingesting 

 certain kinds and rejecting others in a systematic way. Butschli 

 ('89) supports Ehrenberg's view. He concludes that protozoa do 

 not possess the power of choice, and Verworn ('89) likewise con- 

 cludes, on the basis of rather extensive experiments, that there is 

 no selection. 



Jennings ('02). states that Vorticella and Stcntor probably do 

 not have the power of selecting their food in any precise way. 

 Mast ('09) in his work on Didiniitin shows that the apparent 

 choice of food on the part of this organism is 'due to the fact 

 that the seizing organ will adhere to the surface of some organisms 

 and not to others. The didinia come in contact with all sorts of 

 objects in their random swimming and " select " as food only those 

 to which the seizing organ will adhere. 



Schaeffer ('10) in his work on Stcntor cccrulcus concludes that 

 this organism exercises a very definite selective power and dis- 

 criminates very accurately between organisms and indigestible 

 particles, and that it discriminates even between different organ- 

 isms. He contends that it selects its food on a tactual basis, and 

 apparently not on a chemical one. The same worker ('16) reports 

 some experiments on Amoeba and maintains (p. 562) that although 

 Amoeba eats insoluble substances, there is a slow process of learn- 

 ing in favor of selection. He ascribes to the endoplasm of Amceba 

 a more specific power of discrimination than to the ectoplasm, and 

 also maintains that movement of an object is a very important 

 factor in determining whether or not it shall be eaten. 



Calkins ('10) says, "while mpst of the protozoa wait until the 



