OKGANIC MOVEMENTS 21 



organised with regard to their locomotory organs, the number 

 of motor possibilities is more restricted : Paramecium for 

 instance always swims backward, revolves round the axis, 

 and turns to the aboral side. That might seem to be a 

 typical reflex, but in fact is far from being so. One of 

 the components of the motor reaction allows an indefinite 

 variety of motions at random even here the revolving 

 round the long axis. This act may be performed to any 

 possible amount, and, of course, the slightest variety in 

 performing it would bring the animal to quite a different 

 part of the dish in the course of its subsequent movements. 

 Jennings has introduced the appropriate name of " action 

 system " to signify the typical restriction of possible move- 

 ments, indefinite l in spite of it, which are founded upon 

 the typical locomotory organisation : it is clear that all 

 higher animals possess such a system, and that man for 

 instance is restricted by it from flying. 



Thus then all single motor acts that could be actually 

 observed were found to be of the type of " movement at 

 random," occurring either on a definite action system or 

 on an absolutely indefinite one. There was scarcely any 

 reflex of the true kind, in the sense of an absolutely fixed 

 correspondence of locomotory cause and effect 



The Modifialility of Single Motor Acts 



The concept of the contingency of single motor acts 

 embraces the fact of their modifiability. But as our mind 

 is forced to conceive all that happens as being univocally 



1 We might speak here of an indefiniteness of different orders, as 

 mathematics does. 



