CHAP. X Instinct 155 



the organism acts as a whole ; it reacts to its environment, 

 and in time performs " voluntary " actions. 



The acts of the parts of an organism may be — 

 (i) "Automatic," as, for example, the beating of the 

 heart. 



(2) Reflex, as, for example, the intestinal movements 



which force the food through the alimentary 

 canal, or the movements involved in sneezing. 



(3) Mixed actions which are partly automatic and 



partly reflex, such as the respiratory movements. 

 The movements of the entire organism may be of a very 

 complex nature. They may be — 



(i) Reflex; as when we start at a sudden noise. 



(2) " Innate," commonly called instinctive ; these are 



best observed in newly-born animals, for in them 

 intelligence, which must be based upon experience, 

 is necessarily at a minimum. 



(3) " Habitual," such as are rapidly learned and are 



then performed without mental effort, which imply 

 an innate capacity, and are therefore allied to (2). 



(4) Intelligent, such as imply mental activity, which 



consists in the combining and rearranging all the 



other possible acts of the order — (i), (2), or (3) ; 



and which may be recognised in all adaptations 



to novel circumstances. 

 This classification possesses most obvious faults, but it 

 has certain advantages. It reveals some of the difficulties 

 that delay the would-be definer of instinct. For the essen- 

 tial criterion of an instinctive action is that all the machinery 

 for its performance, as a reflex to a certain stimulus, lies 

 ready formed within the organism ; but the apparently in- 

 soluble questions present themselves. How soon may not 

 actions be modified by intelligence ? and How in a mature 

 animal with considerable experience is one to separate 

 the purely instinctive acts from the intelligently modified 

 instinctive acts ? 



Also it is evident that "habitual" actions may be "instinct- 

 ive" actions deferred until the creature be further devel- 

 oped, as the flight of many birds is deferred ; or they may 



