110 THE THEORY OF EVOLUTION 



their action is monotonous.' l The dog, however, who 

 strives after his food takes account of the hindrances 

 as they present themselves he acts individually to 

 a definite end ; for that there suffices no organism of 

 machine-like arrangements, and therefore there is no 

 reflex activity. 



All organisms, however, do not behave like the dog ; 

 there are many to which none of the three criteria apply 

 which are used in comparative physiology in the search 

 for conscious (' psychic ') vital expressions, and which 

 require the acceptance of true recognition and voluntary 

 power of striving. There are lacking, namely, in the 

 first place the easily observable external signs of spon- 

 taneous (voluntary) movements seen in the larger 

 organisms ; a use or a necessity for the vital impulse 

 appears, furthermore, to be excluded, since reflex and 

 other arrangements in the construction secure the 

 undisturbed performance of all the vital functions ; 

 finally the ' organs/ which may resemble animal ones, 

 show themselves in the clearest way to be arrangements 

 for the reception of definite external e impulses/ The 

 first two criteria the lack of voluntary motion and 

 the absence of any necessity for the vital impulse- 

 can be deduced directly from the absence of sense 

 faculties in ' plants ' ; the third the possession of 

 special ' organs ' proves nothing, if it be not previously 

 declared what has to be proved. Since, however, 

 there are frequent references to the new investigations, 



1 F. Lucas: Psychologic der niedersten Tiere, Vienna and Leipzig, 1905, 

 p. 11. 



