CONFORMITY WITH PLAN 275 



execution of the action is not conditioned, but plastic. And 

 it may remain plastic, if the effectors have a fixed shape, and 

 only the rule of their use is influenced from without by means 

 of the excitation ; in this case, the framework cannot be lodged 

 mechanically in the action-organ, but in its formation follows 

 the rhythmic law of the impulses. 



This is typical of the course of the processes described as 

 instinctive actions in the steering-mechanism of animals. 

 The extraordinary number of separate movements, which fit 

 into one another in conformity with plan during the course 

 of an instinctive action, makes it difficult, however, to assume 

 a prepared framework in the steering-mechanism that would 

 be adequate to these demands. The plasticity shown in the 

 execution of the instinctive action makes such an assumption 

 impossible. 



If now we observe the actions of the funnel-roller beetle 

 or the ichneumon-fly, we may note again and again that these 

 are influenced by a number of external indications, and yet 

 proceed according to laws of their own. The number and the 

 nature of the indications is absolutely immutable, but they 

 need not all become effective at each action. Since the 

 animal is quite incapable of receiving new indications, the 

 taking up of indications remains strictly reflex and quite 

 non-plastic. The plasticity of the actions performed comes 

 about only through the animal having at its disposal a larger 

 number of indications, and this enables it to accommodate 

 itself within a wide range to the external circumstances that 

 offer, by altering the rhythm of its action-sequence according 

 to the difference in the indications. 



Again we see the two rules at work in order to give the 

 actions their especial stamp, — the rule of working, controlling 

 the mechanical course of the process in the steering-mechanism, 

 and the rule of direction, which, by modifying the working, 

 introduces plasticity into processes that otherwise would run 



