1898.] on Instinct and Intelligence in Animals. 569 



Even with these specially selected subjects for investigation, however, 

 it is only by a sympathetic study and a careful analysis of their 

 behaviour that what is congenital can be distinguished from what is 

 acquired ; for from the early hours of their free and active life, the 

 influence of the lessons taught by experience makes itself felt. Their 

 actions are the joint product of instinct and intelligence, the con- 

 genital modes of behaviour being liable to continual modification in 

 adaptation to special circumstances. Instinct appears to furnish a 

 ground plan of procedure, which is shaped by intelligence to the 

 needs of individual life, and it is often hard to distinguish the 

 original instinctive plan from the subsequent intelligent modification. 



It is not my purpose to describe here in detail, as I have done 

 elsewhere, the results of these observations. It will suffice to indicate 

 some of the more salient facts. In the matter of feeding the callow 

 young of such birds as the jackdaw, jay or thrush instinctively open 

 wide their beaks for the food to be thrust into their mouths. Before 

 the eyes have opened, the external stimulus to the act of gaping would 

 seem to be either a sound or the shaking of the nest when the parent 

 bird perches upon it. Under experimental conditions, in the absence 

 of parents, almost any sound, such as a low whistle, lip-sound, or click 

 of the tongue, will set the hungry nestlings agape, as will also any 

 shaking or tapping of the box which forms their artificial nest. And 

 no matter what is placed in the mouth the reflex acts of swallowing 

 are initiated. But even in these remarkably organic responses the 

 influence of experience soon makes itself felt. For if the material 

 given is wrong in kind or distasteful, the effect is that the bird ceases 

 to gape as before to the stimulus. Nor does it continue to open the 

 beak when appropriate food has been given to the point of satisfac- 

 tion. These facts show that the instinctive act is prompted by an 

 impulse of internal origin, hunger, supplemented by a stimulus of 

 external origin, at first auditory, but later on, when the eyes are 

 opened, visual. They show also that when the internal promptings 

 of hunger cease, owing to satisfaction, the sensory stimulus by itself 

 is no longer operative ; and they show, too, that the diverse acts of 

 gaping and swallowing become so far connected that the experience 

 of distasteful morsels tends, for a while at least, to prevent further 

 gaping to the usual stimulus. 



With those birds which are active and alert soon after hatching, 

 the instinctive acts concerned in feeding are of a different character. 

 At first, indeed, the chick does not peck at grains which are placed 

 before it, and this is probably due to the fact that the promptings of 

 hunger do not yet make themselves felt, there being still a considerable 

 supply of unabsorbed yolk. Soon, however, the little bird pecks with 

 much, but not quite perfect, accuracy at small near objects. But 

 here again experience rapidly plays its part. For if distasteful 

 objects, such as bits of orange peel, are the first materials given, 

 pecking at them soon ceases; and if this be repeated the little bird 

 cannot be induced to peck, and may even die of starvation. This 



