462 Journal of Comparative Neurology and PsycJwlogy. 



be called a reflex — a term which I have applied to it in previous 

 papers. The question which interests us here is not whether 

 an act performed without the intervention of a nervous system 

 may properly be called a reflex ; it may be strongly doubted 

 whether the anatomical structure of organisms forms a proper 

 basis for classification of types of behavior. But does the re- 

 action method described fall in the concept of a reflex, judged 

 merely as a type of behavior ? 



A reflex is commonly described as a fixed and invariable 

 method of response to a definite stimulus. It is rare, however, 

 that such definitions are found to be rigidly maintainable for 

 given instances; the excellent discussion of Hobhouse (1901) 

 shows how the reflex concept must be modified and its limits 

 effaced, till it flows easily into other behavior types, before it 

 can be applied to the phenomena actually found in animal be- 

 havior. Such a process of softening down is certainly neces- 

 sary before we can make the reflex concept apply to the avoid- 

 ing reaction of Paramecium. This reaction is composed of 

 three factors, which may vary more or less independently of 

 one another, in such a way that an absolutely unlimited number 

 of combinations may result, all fitting the common reaction 

 type. The possible variations may be expressed as follows: 

 If the Paramecium be taken as a center about which a sphere 

 is described, with a radius several times the length of the ani- 

 mal, then as a result of the avoiding reaction the Paramecium 

 may traverse the peripheral surface of this sphere at any point, 

 moving at the time either backward or forward. In other 

 words, the reaction may carry it in any one of the unlimited 

 number of directions leading from its position as a center. 

 While the direction of turning is absolutely defined by the 

 structure of the animal, yet the combination of this turning 

 with the revolution on the long axis permits the animal to reach 

 any conceivable position with relation to the enviroment. In 

 other words, Paramecium, in spite of its curious limitations as 

 to method of movement, is as free to vary its relations to the 

 environment in response to a stimulus as an organism of its 

 form and structure coiild conceivably be. 



