APPETITES AND AVERSIONS. 93 



tation (also, in some cases, in later performances) of many in- 

 stincts, the animal begins with an incipient consummatory action, 

 although the appeted stimulus, which is the adequate stimulus 

 of that consummatory action, has not yet been received. I 

 speak of an incipient "action" rather than "reaction," because 

 it seems clearly wrong to speak of a "reaction" to a stimulus 

 which has not yet been received. The stimulus in question is 

 obtained only after a course of appetitive, trial-and-error be- 

 havior. When at last this stimulus is obtained, the consumma- 

 tory reaction takes place completely, no longer incipiently. 

 Then the appetitive behavior ceases; in common speech we say 

 the animal is "satisfied." 



One may observe all gradations between a true reflex and a 

 mere readiness to act, mere facilitation. Thus, in the dove, a 

 stimulus from food in the crop may cause the parent to vomit the 

 food or to feed it to young: there are all gradations from an im- 

 mediate crop-reflex, in which the food is vomited upon the ground, 

 through intermediate cases in which the parent is much disturbed 

 by the food in his crop, but appetitively seeks the young and 

 induces them to take the food ; to other cases is which the parent 

 is only ready to feed the young if importuned by them ; and finally 

 to cases in which the stimulus from the crop does not even cause 

 facilitation, and the parent does not disgorge the food at all, even 

 if importuned by the young. 



While an appetite is accompanied by readiness for certain 

 actions, it may be accompanied by a distinct unreadiness for 

 certain other actions, and this is an important factor in some 

 forms of behavior. It is altogether probable that this unreadi- 

 ness is due in some cases to the fact that the activity of certain 

 neurones inhibits the activity of certain other neurones. It is 

 now well-known, too, that unreadiness may be due to the con- 

 dition of the internal secretions. And the mutual exclusion of 

 certain forms of instinctive behavior is inevitable, due to the 

 incompatibility (Washburn, '16) of their motor components. 



Unreadiness may be accompanied by aversion, and vice versa; 

 but either of these may occur without the evident presence of 

 the other. An aversion is sometimes accompanied by an in- 

 nately determined reaction adapted to getting rid of the disturb- 



