Intelligence and Experience 81 



the result of personal trial or experience, is 

 attributable to the re-excitation of impressions 

 made by repeated similar kinds of stimuli on 

 the mnemic elements of nerve cells. Intelli- 

 gent behaviour involves the modifications in the 

 action of those elements which constitute the 

 agency by which instincts become manifest. 1 



Among invertebrates, instinctive movements 

 have reached their highest point of perfection 

 in ants and bees, and we find a corresponding 

 development of their central nervous system, 

 for if there is one organ of the body more than 

 another which increases in complexity as evolu- 

 tion proceeds it is the brain. 



The central nervous system of insects con- 

 sists of a brain and a chain of ganglia extending 

 along the ventral part of the animal's body, 

 which in many instances are found to have 

 undergone concentration longitudinally. From 

 this chain of nervous matter sensory and motor 

 nerves pass to the structures forming the 

 animal's body; it is continued upwards into 

 the lower brain. 



1 Psychology, "The Study of Behaviour," by William McDougall, 

 F.R.S., p. 164; also "Instinct and Experience," by Prof. Lloyd 

 Morgan, pp. 7, 9, 12, 27, 32. 



