86 THE BEHAVIOR OF PROTOZOA 



which it was shown that when Stentor was offered either 

 alternately or at the same time nutritious objects such as 

 Phacus or Euglena and such substances as starch grains, 

 powdered carmine or India ink, fine sand or sulphur, the 

 former would be swept into the gullet and ingested, while 

 the latter would usually be rejected. Conditions of hunger 

 or satiety influence the selection of food. Very hungry 

 Stentors may ingest indigestible particles of carmine or 

 India ink, but when better fed the discrimination is more 

 precise and only digestible material is taken in. Hungry 

 Stentors differ from well fed ones also in the greater extension 

 of the body and the greater activity of the membranellse, 

 but they are less responsive to mechanical stimuli. 



The behavior of Protozoa, as we have seen, is influenced 

 by their previous activity as well as by changes of external 

 conditions. That behavior should be modified by these 

 things is of course inevitable, for no organism is ever twice 

 the same, and the life of every organism is one of constant 

 adjustment to the external world. How far these changes 

 indicate the presence of mind is a question about which 

 there is much dispute. These changes are to a considerable 

 degree of an adaptive nature, but the same may be said of 

 many purely physiological processes occurring in our bodies. 

 There are some phenomena described which have been 

 interpreted as the acquirement of habit and even as learning 

 by experience, but the observations on this score scarcely 

 justify, in the opinion of the writer, the interpretations 

 that have been placed upon them. Mr. Stevenson Smith 

 has performed some experiments which lead him to the 

 conclusion that Paramceciurn is able to acquire advantageous 

 habits. He placed a Paramoecium in a fine tube containing 

 a small amount of water. The inner diameter of the tube 

 was less than the length of the Paramoecium, so that the 



