BEHAVIOR OF UNICELLULAR ORGANISMS. m 



affinities and repulsions between the protoplasmic substance 

 and other chemical compounds. Like all the other tactic 

 phenomena, it is the result of a motor reflex, which may be pro- 

 duced by the most varied means. These tactic movements, 

 then, do not establish an immediate relation between the move- 

 ments of organisms and the movements characteristic of inor- 

 ganic substances. The organism reacts as an individual, not 

 as a substance. To my mind the facts above brought out in 

 regard to the movements of these creatures tend, if these facts 

 have a general validity, to deprive such movements of their 

 supposed value for explaining or illustrating the processes of 

 growth ; in so far as the ideas of chemotaxis and the like 

 in growth processes have been derived from the phenomena 

 exhibited by unicellular organisms, these ideas require a revision. 



Especially do the facts above brought out reveal the fal- 

 lacy of the statement so often insisted upon, that the growth 

 processes induced by chemical or physical agencies are " the 

 same as " or " identical with " the locomotor reactions induced 

 by the same agencies. This has been carried so far that stren- 

 uous objection has been raised even to the use of distinguishing 

 terms for these two sets of phenomena. We are told that to 

 distinguish as -taxis X\\q motor reactions of a free organism from 

 -tropisni or the growth reactions of a fixed organ or organism 

 is all wrong ; the two are "identical." It is reasonably certain 

 that the growth phenomena of plants are not brought about 

 through a reflex that is identical with the motor reflex of Para- 

 mecium ; it seems exceedingly probable that the ways by which 

 movements are brought about as responses to stimuli in the 

 various classes of plants and animals will present great variety. 

 It is difficult to see what is to be gained except confusion of 

 ideas by applying the same names to two such dissimilar 

 activities as the motor reflex of Paramecium when stimulated 

 by a chemical, and the bending of a plant to or from a chemi- 

 cal in solution. 



In regard to the second question touched upon in my intro- 

 duction, — the nature and importance of the activities of uni- 

 cellular organisms as compared with those of many-celled 

 creatures, and their value for explaining the phenomena shown 



