94 WALLACE CRAIG. 



ing stimulus, or this point is of special interest by two alter- 

 native reactions which are tried and interchanged repeatedly 

 until the disturbing stimulus is got rid of (see example 7, page 100). 



The escape from a disturbing situation or the attainment of 

 an appeted one is accomplished, in case of some instincts, far 

 more surely and more rapidly after one or more experiences. 

 In the first performance of an appetitive action, the bird makes 

 a first trial; if this fails to bring the appeted stimulus he remains 

 agitated and active, and makes a second trial, which differs more 

 or less from the first; if this fails to bring the appeted stimulus he 

 remains still active and makes a third trial; and so on until at 

 last the appeted stimulus is received, the consummatory reaction 

 follows, and then the bird comes to rest. In later experience 

 with the same situation, the modes of behavior which were fol- 

 lowed immediately by the appeted stimulus and consummatory 

 reaction are repeated; those which were not so followed tend to 

 drop out. 



If a young bird be kept experimentally where it cannot obtain 

 the normal stimulus of a certain consummatory reaction, it may 

 vent that reaction upon an abnormal or inadequate stimulus, and 

 show some satisfaction in doing so; but if the bird be allowed at 

 first, or even later, to obtain the normal stimulus, it will be there- 

 after very unwilling to accept the abnormal stimulus. That this 

 is true of the sex instinct has been shown in a former article 

 (Craig, '14). It is true also of the appetite for a nest. Thus a 

 female dove which has never had a nest, nor material to build 

 one, lays eggs readily on the floor; but a dove that has had long 

 experience with nests will withhold her egg if no nest is obtain- 

 able. The male dove similarly, if he has never had a nest, goes 

 through the brooding behavior on the floor; but an experienced 

 male is unwilling to do so, and shows extreme anxiety to find a 

 nest. These examples illustrate the fact that the bird must learn 

 to obtain the adequate stimulus for a complete consummatory 

 reaction, and thus to satisfy its own appetites. 



There is often a struggle between two appetites, as when a bird 

 hesitates, and it may hesitate for a long time, between going on 

 the nest to incubate and going away to join the flock, eat, etc. 

 By watching the bird one can predict which line of behavior it 



