228 THE BEHAVIOR OF LOWER ORGANISMS. 



The method by which, through the negative reaction, Amoeba avoids 

 an injurious agent is of interest. The animal does not go directly away 

 from the injurious agent, as by moving toward the side opposite that 

 stimulated. It moves in any direction except toward the region stimu- 

 lated. There is no system of conduction such that strong stimulation in 

 a given spot involves movement directed toward the opposite side. If 

 the movement in the new direction induces a new stimulation, the direc- 

 tion isagain changed. This may be continued until the original direction 

 of movements is squarely reversed. The method is akin to that of trial 

 and error in higher organisms (see Morgan, 1894, pp. 241-242). 



(c) The food reaction is directly adaptive in that it procures food. 

 As a rule this reaction occurs only when the source of stimulation is 

 fitted to serve as food. Empty diatom shells, sand grains, debris, etc., 

 are, as a rule, not taken into the body, as many observers have pointed 

 out. Sometimes material is taken into the body that is not useful, as 

 is described by Rhumbler (1898, p. 236). In such cases there is no 

 evidence of a food reaction in the sense characterized above ; the 

 material is ingested accidentally, as it were, through its adherence to 

 the protoplasm. The food reaction, as a definite form of behavior, is 

 always adaptive so far as known. 



(</) Some of the habits of Amoeba, characterized above, are clearly 

 adaptive. The use of the antenna-like pseudopodium sent out by 

 Amoeba velata and A. angulata is evident. Penard describes in detail 

 how Amozba velata uses it in passing from one substratum to another. 



The habit which some Amoeba? have, when suspended freely in the 

 water, of sending out pseudopodia in all directions (p. 181) is, of course, 

 useful in that it increases the chances of coming in contact with some 

 solid object, without which the Amoeba cannot move from place to 

 place. 



REFLEXES AND "AUTOMATIC ACTIONS" IN AMOEBA. 



In the behavior of Amoeba we can distinguish factors directly com- 

 parable to the reflexes and " automatic activities " of higher organisms. 

 The responses of Amoeba to stimuli have the nature of reflexes in the 

 fact that they are not direct effects of the physical action of the stimulus 

 (see p. 219), but are determined by the internal conditions of the 

 organism. They may be called reflexes, unless we propose, as certain 

 writers do, to restrict the term reflex to processes involving differen- 

 tiated nerves. The precise designation is unimportant; the essential 

 point is that the responses agree with the reflexes of higher animals in 

 being indirect. 



Ziehen, in his Leilfaden der physiologischen Psychologic (sixth 

 edition, p. ro), defines as automatic acts " motor reactions, which do 



