INSTINCT 109 



ings of many instinctive acts. Hunger drives the lioness 

 to seek for prey; sexual impulses lead to the search for mates; 

 and a bird in confinement may become uneasy when the 

 time for migration arrives. The same thing is even more 

 conspicuously illustrated in the instinct of play. A lamb 

 may frisk about from sheer good feeling. A kitten may 

 crouch and spring as if upon a mouse when there is no ex- 

 ternal object to excite its action. And where the play 

 activities are associated with external objects, the latter 

 serve only to awaken the stored energy of impulse which 

 may be nearly ready to discharge on its own account. The 

 play impulse which may sometimes vent itself in random 

 movements usually takes fairly definite channels of expres- 

 sion which are quite characteristic of particular species of 

 animals. The energies of the young animal tend to dis- 

 charge themselves in movements similar to those which form 

 the regular behavior of the adult, and a certain degree of 

 proficiency is reached in those activities which form the 

 more serious occupations of later life. But the promptings 

 to such behavior are due mainly or wholly to internal 

 impulses. 



The element of internally initiated impulse in instinct is 

 not confined to higher forms. It is probably coextensive 

 with animal life. Amid all the stereotyped responses of 

 the Protozoa we have a large element of activity determined 

 by internal factors. The almost constant swimming of 

 many infusorians, and the regular rhythmical activity of 

 others are, like the beating of the heart and other organic 

 rhythms, the result of causes within the organism. 



It is of course difficult in many cases to ascertain whether 

 activity results, perhaps indirectly, from outer stimulations 

 or from internal changes. In a great many cases the 

 organism needs but a slight provocation to discharge its 



