56 SENSATION AND REACTION 







So far, we have been considering the mechanism 

 by which man and the higher animals maintain 

 a connection with their environment. It includes 

 instinctive (reflex) and ideo-motor systems which, 

 when started by the touch of an impression, act 

 promptly and accurately, and are not interfered 

 with by the functioning of the brain. It also 

 includes a system which, connected with the brain, 

 is swept by a number of conflicting influences. 

 As we descend the scale of animal life, the direct- 

 ing authority of instinct spreads from the internal 

 functioning of the body to its external behaviour : 

 conduct is linked more closely to primary sensa- 

 tions, and there is a narrower field for the exercise 

 of choice. An impulse that is set free by a sensory 

 impression is so directed by instinct as to energize 

 a definite series of actions, often of a very elabor- 

 ate character, which are accurately performed 

 without previous experience. The marvellous 

 regularity and complexity of this directive force 

 is typically illustrated by the life history of insects. 

 A worker bee, immediately it emerges from the 

 pupal stage and sees its surroundings, sets itself 

 to a complicated process of working in wax, with 

 what seems to be practised dexterity and trained 

 intelligence. It is born an efficient mechanic, 

 just as our hearts and lungs are, from the moment 

 of birth, capable of exercising their functions. 

 Birds' nests illustrate very familiarly the posses- 

 sion of similar inborn skill in higher orders of the 

 animal kingdom. We are probably correct in 

 assuming that the functioning of the internal 

 organs of the body, the growth of the body and 

 the development of the embryo are all guided by 

 this process of instinctive direction. 



We are profoundly ignorant of the nature of this 

 wonderful directive force. Its impulses do not 



