ANIMAL BEHAVIOUR 183 



there is no further obstacle to progress. In this direction it 

 continues. Through systematically testing the surroundings, 

 by swinging the anterior end in a circle, and through per- 

 forming the entire reaction repeatedly, the infusorian is 

 bound in time to find any existing egress from the difficulties 

 even though it be but a narrow and tortuous passageway " 

 (Jennings, 1906, p. 49). 



The behaviour of Paramecium is very instructive in its 

 combination of effectiveness and simplicity. It drives itself 

 forward in a narrow spiral, revolving on its long axis and 

 swerving a little towards the aboral side — such is its 

 action system ; and most of its behaviour consists of slight 

 variations on this simple tune. " It constantly feels its way 

 about, trying in a systematic way all sorts of conditions, 

 and retiring from those that are harmful. Its behaviour 

 is in principle much like that of a blind and deaf person, 

 or one that feels his way about in the dark. It is a con- 

 tinual process of proving all things and holding to that 

 which is good" (Jennings, 1906, p. 106). 



^^ The behaviour and reactions of Paramecium consist on 

 the whole in performing movements which subject the or- 

 ganism to varied conditions (using this word in the widest 

 sense), with rejection of certain of these conditions, and 

 retention of others. It may be characterized briefly as a 

 selection from among the varied conditions brought about 

 by varied movements" (Jennings, 1906, p. 108). On the 

 whole the animalcule rejects or avoids what is injurious and 

 accepts or seeks what is beneficial, just as higher animals 

 and men do. The behaviour is adaptive and purposive. In- 

 deed Jennings goes the length of saying: " In no other group 

 of organisms does the method of trial and error so completely 

 dominate behaviour, perhaps, as in the Infusoria." 



