16 THE RIDDLE OF MIGRATION 



nearly always lies an intermediate link termed the 

 association neurone and there may be many of them 

 rather than one. They greatly multiply and com- 

 plicate the connections in the cord. The local 

 stimulus, such as our drop of acid, may thus call 

 into action motor neurones up and down the length 

 of the spinal cord. (Fig. 1, B.) 



Where then, it may well be asked, does the brain 

 come in? An example will make the answer plain. 

 When we sneeze we are exhibiting a simple reflex 

 response to nasal irritation. Under normal circum- 

 stances we heartily indulge ourselves. But should 

 we be seized with a desire to sneeze in the middle 

 of a prayer at church, we suppress the impulse and 

 refrain from sneezing. The brain, or rather a cer- 

 tain section of it, overrules a perfectly natural reflex 

 action. Possession of it enables us to exercise judg- 

 ment and control. This implies an understanding 

 of the circumstances and reasoned, intentional ac- 

 tion to suit it. This is really what the term intelli- 

 gent behaviour means. The greater the develop- 

 ment of this part of the brain, the higher is the 

 standard of intelligence that can be expected from 

 the individual. It has unquestionably attained the 

 greatest degree of perfection in man and reaches a 

 remarkably high level in some other mammals, 

 notably in the higher apes. Our next aim must 



