436 'Jounwl of Comparative Neurology and Psychology. 

 THE TROPISMS. THEORIES OF ORIENTATION. 



In the treatment of the reactions of the lower animals many 

 writers have apparently considered the direction of movements as 

 the only feature worthy of attention, with the consequent reduction 

 of the reactions to positive and negative tropisms. A universal 

 form of movement as a mode of orientation to stimuli has even 

 been formulated, which is supposed to sufficiently describe a 

 priori the behavior under stimulation. The animals are regarded 

 in reality as passive factors in the result, having their movements 

 miposed upon them. This conception of an animal's movements 

 manifestly is a homologue of the notion of spontaneous generation. 

 The movements are virtually represented as directly produced by 

 the action of the environment. 



Other writers have shown clearly what scarcely needs to be 

 pointed out, that an animal's behavior is as characteristic as its 

 structure. One of the first fruits of comparative study of behav- 

 ior has been to replace the old notion of the production of move- 

 ments by the action of the environment, akin to the spontaneous 

 generation of organisms, by descriptions which are in some cases 

 as definite as those of anatomical structure which we possess. 

 This later view finds in animal behavior an external exhibition 

 of regulatory activity, and treats movements as self-regulative 

 rather than externally controlled. 



The most extreme exhibition of this later tendency is a propo- 

 sition to explain tropisms on a basis of accidental orientation, or 

 trial and error, rather than to allow the directive action of external 

 stimuli. Butthisviewrepudiates the adaptive character of directed 

 movements as clearly as did the belief in movements produced 

 directly by the action of the environment. The theory is that 

 under stimulation animals make varied movements. Those that 

 are in such a direction as to lead to decrease of stimulation, are 

 continued because of the absence of stimulus to further change. 

 In the older view orientations were forced by the environment. 

 According to this point of view orientation is regarded as acci- 

 dental. Such a roundabout method as is implied in the selection 

 of varied movements is manifestly less self-regulative than a more 

 direct response to a stimulus would be. It means that the animal 

 in question is regarded as having no power of immediately regu- 

 lating its actions with reference to the direction of an external 

 stimulus. 



