30 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



is due. Of course these simple phenomena would be 

 perfectly intelligible on the machine-theory. 



Unfortunately they are not so common as Loeb and 

 others thought them to be. The next class of combined 

 motions, first established by von Uexkuell, already forces 

 us to introduce some other elemental nervous phenomena 

 besides mere stimulation and nervous conduction. This 

 type is seen in the progressive movements of many lower 

 animals, but also, as shown by Sherrington, 1 in the move- 

 ments of vertebrates, so far as they depend on the spinal 

 cord only. The most simple scheme of the class is 

 expressed by the fact, that every motor stimulation in 

 " simple nerve-nets " always relates to those muscles which 

 are not contracted but extended, whether passively or 

 actively. This scheme of course takes no account of the 

 stimulation, but simply states that, if the stimulation is 

 given and if the organisation of an animal with regard to 

 its muscles is such as it is, the kind of movement is 

 determined in the very simple manner we have mentioned. 

 Many of the rhythmical movements in walking are explained 

 in this way. They depend on the antagonistic character 

 of certain muscles : one muscle has just the opposite effect 

 to another, so that, if the one is contracted, the other is 

 extended ; the latter therefore receives the stimulation and 

 contracts ; then the other extends, is therefore stimulated, 

 contracts, and so on. 



Of course there would be no difficulty in understand- 

 ing on a purely mechanical hypothesis this simple class 

 of combined movements, in which only one elemental 



1 Ergebnisse d. Physiol. 4, 1905 ; The Integrativc Action of the Nervous 

 System, New York, 1906. 



