Reactions of /Eolosoma to Chemical Stimuli Jl 



2. The direction of the impinging stimulus — Hnes of force or of 

 diffusion — affect tlie direction of the resulting reflex only inci- 

 dentally. The morphology of the organism is the determining 

 factor. 



3. The intensity of an impinging stimulus, or variations in its 

 intensity, are significant in so far as they interrupt the physiologi- 

 cal poise of the organism involved. They may determine the 

 vigor of, but not the sort of, reaction that may be expressed. 



With these facts in mind, we may attempt an outline of the 

 phylogenetic rise of the action system of iEolosoma in so far as it 

 had been analyzed in this investigation. The basis of behavior 

 rests upon the irritability of living protoplasm. A thoroughgoing 

 interpretation of this irritabihty is yet to be made; it is far beyond 

 the range of our present experimental knov^ledge of protoplasm. 

 This much vi^e do know^ — irritability presupposes movement, and 

 the use of movement formulates the quest of "behavior." All of 

 the movements potential to the protoplasmic aggregates, which 

 we designate as an individual organism, are variously being 

 expressed in the course of its life history (Jennings, '07). Some of 

 these movements, in periods of stress, more readily than others, 

 restore a certain physiological equilibrium, which is essential to the 

 welfare of the organism, and which has been disturbed by the 

 impingement of an external source of energy. Repetition of 

 equivalent conditions of stimulation tends to reproduce such 

 movements with increasing celerity, under the law of the readier 

 resolution of the physiological states (Jennings, '04), By the pro- 

 cess of natural selection these movements have been selected into 

 a system of characteristic reactions which we designate as the 

 "action system." The rise of an action system has further played 

 a profoundly morphogenetic role in the course of history of the 

 organism (Bohn, '06). The animal is what it is because of past 

 behavior. 



This brief outline is esentially a recapitulation of the "trial and 

 error" theory of the rise of behavior as advocated by Jennings, or 

 the selection of random movements as suggested by Holmes. 



It attempts to balance the play of both internal and 

 external forces in the rise of an individual animal economy. There 



