ANIMAL BEHAVIOUR 195 



whole, so behaviour differs from tropisms in being an effec- 

 tive concatenation or correlation of successive adjustments. 

 In a tropism there is really but one adjustment, which is 

 repeated over and over again. In behaviour there is trial 

 after trial of different reactions, and a selection of the best 

 available result. 



§ 7. N onrintelligent Experimentation. 



Preoccupation with reflexes and tropisms is apt to lead 

 to an ignoring of the ' trial movements ' which are common 

 among the lower animals. " Unprejudiced observation of 

 most Invertebrates will show that they perform many move- 

 ments which have no fixed relation to sources of external 

 stimuli, but which do serve to test the surroundings and 

 thus to guide the animal " (Jennings, p. 247). Prof. S. J. 

 Holmes writes to the same effect and gives many illustra- 

 tions : — " The lives of most insects, crustaceans, worms, and 

 hosts of lower Invertebrate forms, including even the Pro- 

 tozoa, show an amount of busy exploration that in many 

 cases far exceeds that made by any higher animal. Through- 

 out the animal kingdom there is obedience to the Pauline 

 injunction, ^ Prove all things, hold fast that which is good ' " 

 (quoted by Jennings, p. 250). 



Among simple multicellular animals there is, one must 

 admit, not a little of that restless locomotion which we see 

 in Infusorians and the like, which we have called general 

 organismal activity. But at any moment this may give 

 place to more definite behaviour. The creature commands 

 its course and is neither blown hither and thither by every 

 tropistic gust nor bound by reflex routine. It makes sensori- 

 motor experiments which work towards an end, such as the 

 systematic exploration of a corner in search of food. It 



