PROGRESS OF PSYCHOLOGY. 461 



and shunting the stimuli, and a motor nerve passing 

 from the ganglion to a muscle. 



Up to a certain level in the animal kingdom the 

 behaviour is on the whole very simple, and from a 

 physiological point of view may be summed up in 

 the phrase " reflex action." 



"A reflex is a reaction which is caused by an ex- 

 ternal stimulus, and which results in a co-ordinated 

 movement, the closing of the eyelid, for example, 

 when the conjunctiva is touched by a foreign body, or 

 the narrowing of the pupil under the influence of light. 

 In each of these cases, changes in the sensory nerve- 

 endings are produced which bring about change of con- 

 dition in the nerves. This change travels to the cen- 

 tral nervous system, passes from there to the motor 

 nerves, and terminates in the muscle-fibres, producing 

 there a contraction. This passage from the stimulated 

 part to the central nervous system, and back again to 

 the peripheral muscles, is called a reflex. There has 

 been a growing tendency in physiology to make reflexes 

 the basis of the analysis of the functions of the central 

 nervous system, consequently much importance has 

 been attached to the underlying processes and the nec- 

 essary mechanism." * 



The question to which so much attention has been 

 turned in the closing years of the nineteenth century 

 is as to the proportion of animal behaviour which 

 can be covered by this concept of reflex action. At 

 what level do animals begin to learn, to profit by 

 experience, to adapt their behaviour to novel condi- 

 tions? Moreover, what security is there in the as- 

 sumption that the reflex actions which are simplest 

 are also the most primitive ? To what extent may they 



* J. Loeb, Comparative Physiology of the Brain, 1901, 

 pp. 1-2. 



