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 membranelle, 
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 Parameecium is able to acquire advantageous 
habits. He placed a Paramcecium in a fine tube containing 
a small amount of water. The inner diameter of the tube 
was less than the length of the Paramecium, so that the 
