14 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



If the taxis is combined with or followed by movement, 

 there will, of course, be a specific direction in this move- 

 ment also. 



The word " taxis " thus applies only to the correspondence 

 of directions. It does not say the least thing about the 

 means of movement, by which the orientation of the organ- 

 ism goes on ; it does not even seek to point out that the 

 process of orientation is quite a simple process. In fact, 

 a very easy consideration shows that the process of " taxis " 

 is by no means simple in many cases. 



Imagine an organism, say a protozoon or a crayfish, in 

 order to show from the beginning that the particular motor 

 organs in question are of no consequence and imagine it 

 placed with its long axis at a certain angle towards the 

 direction say of the rays of light proceeding from a radiant 

 point. Then " taxis," in this case " phototaxis " or " helio- 

 taxis," would be said to occur, if the organism carries out 

 some sort of turning movement so long as there is any 

 deviation between the direction of its axis and the rays of 

 light ; the movement being performed equally well by the 

 cilia of the protozoon or by the legs of the crayfish. 

 Certainly the " taxis " here is neither immediate nor simple ; 

 it is a combination of very many single motor acts, leading 

 to taxis as a result, though this result must be said to have 

 been reached in an unbroken line. We have to assume 

 that the motor organs of one side of our organism are 

 stimulated by the rays of the light as long as there is no 

 symmetrical arrangement of both of its sides with regard 

 to the direction of the light ; of course, the result of 

 stimulation of this kind would be finally a symmetry of 

 orientation. 



