The Mind of the Simplest Animals 57 



group known as Flagellata, the members of which have in 

 place of cilia a long whiplike protoplasmic filament, and 

 move by lashing it to and fro in the water, indicates that in all 

 of them the negative reaction is the principal feature of be- 

 havior (199, 21 i), and that if any of them possess minds, those 

 minds are of quite as rudimentary a type as that of Amoeba, 

 and very likely rendered even more so, as far as qualitative 

 variety of experience goes, by the predominance of the neg- 

 ative reaction due to greater speed of motion. 



12. Definitions of Tropisms 



Before passing to the study of higher forms of animal life, 

 we may note the meaning of a few technical terms used in 

 describing the behavior of simple animals especially. The 

 direct motor response of an animal to an external stimulus is 

 known as a tropism, from the Greek word meaning "to 

 turn." Various prefixes are attached to this term to indicate 

 the nature of the stimulus concerned; thus phototropism 

 means the reaction of an animal to light; chromotropism, 

 reaction to color ; thigmotropism, reaction to contact ; chemo- 

 tropism, reaction to chemical stimulation; rheofropism, 

 reaction to currents ; geotropism, reaction to gravity ; electro- 

 tropism, reaction to the electric current; anemotropism, 

 reaction (e.g., in winged insects) to wind. Some writers 

 have used instead of tr'opism the word taxis, from the Greek 

 word meaning "to arrange," speaking of chemotaxis, thigmo- 

 taxis, and so on. Phototaxis has, as we shall see, a rather 

 special significance distinct from phototropism. When an 

 animal gives a positive reaction in response to a stimulus, 

 it is said to be positively chemotropic, or phototropic, as the 

 case may be ; when its reaction is negative, it is called nega- 

 tively chemotropic, phototropic, and so on. 



