568 Professor C. Lloyd Moi-gan [Jan. 28, 



instinctive behaviour, are animals concerning wliose mental processes 

 the cautious psychologist is least disposed to express a definite opinion. 

 While the higher mammalia, with whose psychology we can deal 

 •with greater confidence, exhibit less typical instinctSj are more sub- 

 ject to the disturbing influence of imitation, and, from the greater 

 complexity of their behaviour, present increased difficulties to the 

 investigator who desires carefully to distinguish what is congenital 

 from what is acquired. 



Nor do the difficulties end here. For the term "instinct" is 

 commonly, and not without reason, employed by psychologists with 

 a somewhat different significance, and in a wider sense than is neces- 

 sary or even desirable in biology. The naturalist is concerned only 

 with those types of behaviour which lie open to his study by the 

 methods of direct observation. He distinguishes the racial adapta- 

 tion which is due to congenital definiteness, from that individual 

 accommodation to circumstances which is an acquired character. 

 But for the psychologist, instinct and intelligence comprise also the 

 antecedent conditions in and through which these two types of animal 

 activity arise. The one type includes the conscious impulse, which 

 in part determines an instinctive response; the other includes the 

 choice and control which characterise an intelligent act. When a 

 spider spins its silken web, or a stickleback builds the nest in which 

 his mate may lay her eggs, the naturalist describes the process and 

 seeks its origin in the history of the race ; but the psychologist in- 

 quires also by what impulse the individual is prompted to the per- 

 formance. And when racial and instinctive behaviour is modified in 

 accordance with the demands of special circumstances, the naturalist 

 observes the change and discusses whether such modifications are 

 hereditary ; but the psychologist inquires also the conditions under 

 which experience guides the modification along specially adaptive 

 lines. Each has his part to play in the complete interpretation of 

 the facts ; and each should consent to such definitions as may lead 

 to an interpretation which is harmonious in its results. 



In view, therefore, of the special difficulties attendant on a com- 

 bined biological and psychological treatment of the problems of 

 animal behaviour, I have devoted my attention especially to some 

 members of the group of birds in the early days of their life, and 

 I shall therefore draw my examples of instinct and intelligence 

 almost entirely from this class of animals. The organisation and 

 the sensory endowments of birds are not so divergent from those of 

 man, with whose psychology alone we are adequately conversant, 

 as to render cautious conclusions as to their mental states altogether 

 untrustworthy ; when hatched in an incubator they are removed from 

 that parental influence which makes the study of the behaviour of 

 mammals more difficult; while the highly developed condition in 

 which many of them first see the light of day affords opportunity 

 for observing congenital modes of procedure under more favourable 

 circumstances than are presented by any other vertebrate animals. 



