6o BIOLOGICAL LECTURES. 



their lack of reason, which in mysterious ways directed the 

 animal's footsteps and aroused in him by direct inspiration the 

 appropriate act in any set of circumstances, left -us an unfortu- 

 nate legacy in the shape of a tendency to expect an accuracy 

 and infallibility and unchangeableness in animals' reactions 

 such as supernatural inspiration might well give, but which are 

 usually signs of death in the natural world. The common 

 human interest in the marvelous and unusual cooperated with 

 this tendency by selecting for observation such instinctive 

 activities as web-spinning, honeycomb construction, etc., and 

 neglecting the more ordinary activities. Thus arose such 

 amusing expressions as " Failure of instinct." Furthermore, 

 so long as there survived vestiges of this teleological notion of 

 an entity, "instinct" which fitted acts to situations so as to 

 get desirable results, there was the less interest in the real 

 intermediary between situation and act, namely, the nervous 

 system, and less likelihood of men looking for the variations in 

 response to be expected in the results of the activity of any 

 living organ. 



The recognition of the vague in instinctive activity not 

 only brings such activity into line with other biological phe- 

 nomena, and lends a healthier tone to investigation, but also 

 provides a useful warning to the observer. The naturalist who 

 studies a single case of such activity is almost sure to be 

 misled. "In a multitude of witnesses there is strength." 



The utility in the struggle for existence of an animal's 

 equipment of instinctive reactions is much increased by reason 

 of their ability to harden into habits. It is a wide if not 

 a general law that any act which has been performed in a cer- 

 tain situation and resulted in pleasure, or even indifferently, is 

 the more likely to be performed again in that same situation, 

 the reverse happening to any act resulting in discomfort. 



The general manifestations of this law will be dealt with 

 in a later lecture, but its influence on instinctive reactions 

 deserves mention here. First of all, transitory instincts may 

 gain thereby equal value with permanent ones. 



The chick that has followed the mother-hen for six or eight 

 days does not thenceforth need any instinctive impulse to 



