CONFORMITY WITH PLAN 311 



of insects, it is easier to assume that the impulse-systems 

 continually carry on a direct reshaping of the framework. 

 The same holds good with all plastic actions and actions based 

 on experience. With simple actions approximating to reflexes, 

 we may assume the presence of a permanent framework, 

 adjusted once and for all. 



When we have recognised the inner harmonised rhythm 

 as the determining factor, then it is not difficult to deduce 

 from it the actions that lead to the fabrication of the animal's 

 tools, actions which, almost without exception, belong to the 

 instinctive category. 



BEAT-RHYTHM 



In comparison with the general rhythm of the impulses 

 which controls the whole life, the beat-rhythm is very in- 

 significant, for it plays an important part only in the higher 

 animals. A certain beat, it is true, can be observed in all 

 forward movements by animals, because, in these, antagonistic 

 movements of the limbs release one another in regular alterna- 

 tion. But there is nothing to indicate that the beat according 

 to which these movements are set going, is fixed in the interior. 

 On the contrary, the ease with which the limbs of the animal 

 adapt themselves, in their to and fro movement, to the diffi- 

 culties presented by the ground, depends on the lack of an 

 internally fixed beat. As a rule, the free extension of the 

 limbs takes place quicker than the pushing back of the ground, 

 by which the body is driven forward. 



The rhythm of the gait is, in most cases, so well adapted 

 to the condition of the ground, because the excitation flows 

 to the " antagonist," only when that is actually on the stretch. 

 That happens, however, only when the " agonist " has con- 

 tracted, and its representatives have been " locked " against 

 excitation, while those of the extended antagonist are 

 " unlocked." 



