476 



SCIENCE 



[N. S. Vol. XXXIII. No. 84S 



usually reacts first by bending a little to 

 one side. If the particles continue to fall 

 on the disk the beat of the cilia covering 

 the body may suddenly be reversed, thus 

 creating a current tending to carry the 

 offending particles away. If in spite of 

 this the particles still impinge upon the 

 disk the Stentor may contract one or more 

 times. Finally, if all these reactions are 

 tried in vain the infusorian may give a 

 number of violent contractions, break loose 

 from its place of attachment, and swim 

 away. 



It would be an error to interpret the 

 varied behavior of this unicellular organ- 

 ism as a manifestation of intelligence, al- 

 though it is not unlike what the behavior 

 of an intelligent creature might be under 

 the circumstances. No power of learning 

 by experience has ever been discovered in 

 Stentor, or indeed in any other protozoan. 

 The organism is provided with a number 

 of different modes of response, and which 

 one is set in action depends upon internal 

 factors which are influenced by the crea- 

 ture's previous activity. The organism 

 which has responded to a stimulus has be- 

 come transformed into a different mechan- 

 ism which may respond more or le.ss read- 

 ily than before or radically change its 

 method of behavior. 



A striking illustration of varied re- 

 sponses to a given stimulus has been de- 

 scribed by Jennings in the sea anemone 

 Stoichactis. If a foreign body is placed 

 upon its disk the anemone tries to rid itself 

 of the object in various ways. The ten- 

 tacles near the object collapse and the area 

 between them extends, thus producing a 

 relatively smooth surface so that the waves 

 can readily wash the object away. If this 

 does not occur the region under the object 

 begins to swell, thus rendering the removal 

 of the object still easier. If this reaction 

 is unsuccessful the edge of the disk begins 



to sink so that a smooth sloping surface is 

 formed from which the object can readily 

 slide. Here, as in the ease of Stentor, we 

 have an organism capable of reacting in 

 several ways to a given stimulus. What 

 particular reaction is evoked depends upon 

 previous stimulations. 



Modification of behavior caused by dif- 

 ferent conditions of nutrition are found in 

 the lowest members of the animal kingdom. 

 Even the white blood cells after they have 

 ingested a number of bacteria refuse to 

 take in more. Whether there is a limit to 

 the appetite of Amoeba has not been deter- 

 mined, but many infusorians such as Sten- 

 tor, after having swept in a certain amount 

 of food, react to food particles in a quite, 

 different way than when in a himgry con- 

 dition. Hydra when not fed for some 

 time extends the body, sways about in vari- 

 ous directions and keeps up a restless move- 

 ment of its tentacles, thereby increasing its 

 chances of contact with the small creatures 

 which serve as its prey. 



Instances of the non-intelligent modifi- 

 cations of behavior might be multiplied 

 indefinitely. As we pass to higher forms 

 the capacity for responding in different 

 ways to a given situation becomes greatly 

 increased. "Nature," says James in his 

 admirable chapter on instinct, "implants 

 contrary impulses to act in many classes of 

 things, and leaves it to slight alterations of 

 the conditions of the individual case to 

 decide which impulse shall carry the day," 

 and he points out that many animals lose 

 the instinctive demeanor and appear to 

 lead a life of hesitation and choice, not 

 because they have no instincts, but because 

 they have so many of them that they block 

 one another's path. Intelligence in the 

 acceptation of the term which we have 

 accepted begins with the formation of asso- 

 ciations. It does not make its appearance, 

 so far as is known, until a comparatively 



