16 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



point of changing the tactical sense and in the phenomena 

 of simultaneous irritation by different stimuli. 1 But these 

 difficulties might perhaps not be regarded as sufficient to 

 force us to accept vitalism, though, of course, to deny the 

 logical necessity of a mtalistic conception of biological facts 

 does not imply the impossibility of mtalistic agents "being 

 actually at work in them. 



So much about the aspect of the theory of " taxis " a 

 few years ago. 



7. THE WORK OF H. S. JENNINGS. " TRIAL AND ERROR " 



Now it is very important for our present purposes to 

 observe that " taxis," in the sense we have analysed, seems 

 to occur to a rather limited extent only. There is a true 

 and real " galvanotaxis ' : amongst Infusoria, and there are 

 a few " tactical " phenomena in animals, as for instance 

 when Hydra or a flatworm turns its head towards a strong 

 light or towards a mechanical stimulus. But very much 

 of what had been called phototaxis or chemotaxis or 

 thermotaxis, among Protozoa as well as among higher 

 animals, has actually been shown to be not taxis at all, 

 that is, not a final correspondence of direction reached in 

 an unbroken line comparable to the tropisms in plants, 

 but something very different. It therefore must be 

 regarded as possible at least, that in the future still more 

 cases of " taxis " will prove to be illusory, though, as must 

 be mentioned, J. Loeb and certain other writers only 



1 Compare the suggestive article, "Die Lichtsinnesorgane der Algen," by 

 R. H. France, Stuttgart, 1908. France's conception of " Reizvenvertung " 

 originally created by Kolmstamm in a purely psychological sense is very 

 well descriptive of what happens. 



