222 ANIMAL BEHAVIOUR 



and religion this compromise between determinist and free- 

 will interpretations which biology suggests. 



SUMMARY. 



Only in the realm of organisms is there true behaviour in which 

 the creaturr is an agent and exhibits a correlated or concatenated 

 series of acts, effective towards some definite result favourable to 

 the harmony of vital processes and the continuance of the race. 



Among unicellular or non-cellular organisms there is often a 

 restless locomotor activity, hardly on the level of behaviour, which 

 is sustained by the everyday internal functions and is not very 

 clearly separable from them. There are also definite organic re- 

 actions to all sorts of stimuli except sound waves, corresponding 

 in a far-off way to reflex actions in higher animals. In difficult 

 situations there may be a trial-and-error procedure, a selection of 

 the fittest answer and a short-lived modification of behaviour in 

 relation to experience. As Professor Jennings especially has 

 shown, there is among the simplest animals the counterpart of 

 intelligent behaviour. 



Of great interest is the shell-building of some of the arenaceous 

 Foraminifera, where particular materials, such as sponge-spicules, 

 are selected from amid an embarrassment of alternatives, and 

 where the selected material is utilised in a particularly effective way. 



Reflex actions are usually movements of parts, uniform reactions 

 to a particular kind of external or internal stimulus, exhibited ap- 

 proximately to the same extent by all animals of the same kind, 

 and depending on inborn structural linkages of nerve-cells and 

 muscle-cells. But reflexes, though not alterable by expenence, are 

 sometimes controlled by what looks like some appreciation of cir- 

 cumstances. ' Chain-reflexes ' are often broken. 



Another simple form of animal activity is seen in tropisms 

 more or less obligatory movements, like the moth's to the candle, 

 which automatically tend to secure physiological equilibrium in 

 reference to particular stimuli. But the tropistic coercion is some- 

 times successfully thwarted by individual experiment on the part 

 of the organism. 



One of the most important results of recent studies is the proof 

 that many brainless and even ganglionless animals, such as star- 

 fishes and sea-urchins, exhibit a counterpart of the intelligent be- 



