20 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



all movement whatever. So indeed Jennings thought in 

 the first period of his work, but a more thorough study 

 taught him very differently. 



TJic Single Motor Acts. TJie "Movement at Random ' 



This now is the right point to begin the systematic 

 study of the types of animal movements ; let us consider, in 

 the first place, what may be called single motor acts. 



The " simple reflex ' is one of these acts, but it is far 

 from beingr the most original or the most widelv distributed 



ff 



of them ; it seems to be restricted to certain specific types 

 of motion among the higher classes of animals ; even what 

 is performed by our Paramccium is not a simple reflex. 

 The most original motor act, that is to sav, the most 



* * 



elemental one both ontogenetically and systematically 

 (" phylogenetically "), is "motion at random" i.e. an in- 

 definitelv variable motor effect following some sort of a 



/ o 



stimulus and having no specific relation to the locality of 

 the latter, whether the locality of possible stimulation be a 

 limited and fixed one, as for instance in many Infusoria, or 

 not, as in manv higher animals and in all Amoebae. 



* 



There are two classes of original movements at random 

 requiring to be distinguished. The first consists of such 

 single motor acts as show an absolute contingency, the 

 second of those which show a relative one. All Amoebae 

 are a good instance of the first type : any stimulation 

 may be followed by every possible movement in every 

 geometrically possible direction out of a strictly indefinite 

 number of possibilities ; the same holds for many worms. 

 But in Infusoria, as in all animals that are more specifically 



