INTELLIGENT BEHAVIOUR IN INSECTS 123 
acts in special adaptation to new circumstances, and the 
individuality manifested in dealing with the complex condi- 
tions of a variable environment,—these seem to be distinctive 
features of intelligence. On the other hand, in instinctive 
behaviour there seems to be no choice ; the animal is impelled 
to their stereotyped performance through impulse, as by a stern 
necessity ; they are so far from novel that they are performed 
by every like individual of the species, and have been so per- 
formed by their ancestors for generations ; and in performing 
the instinctive act, the animal seems to have no more in- 
dividuality or originality than a piece of adequately wound 
clockwork. 
Granting, then, that behaviour is shown to be intelligent by 
the fact that there is evidence of profiting by experience, we 
inay say that the level attained by the intelligence is indicated 
by the complexity of the adjustment, its precision, the in- 
dividuality shown, the amount of prevision disclosed, and 
in its being such as to extract from the circumstances the 
maximum of benefit. Many of these points, however, serve 
equally well to mark the level of instinctive procedure. 
I].—INTELLIGENT BEHAVIOUR IN INSECTS 
It is, as we have seen, among the higher invertebrates, 
especially in insects, that some of the most remarkable and com- 
plex instincts may be found. ‘There is,* however, a tendency 
to ascribe the behaviour of insects entirely to instinct, without 
sufficient evidence that neither imitation, instruction, nor 
intelligent learning play any part. This is, perhaps, a survival 
of the old-fashioned view that all the acts of the lower animals 
are performed from instinct, whereas those of human beings 
are to be regarded as rational or intelligent. In popular 
writings and lectures, for example, we frequently find some or 
all of the following activities of ant-life ascribed to instinct : 
* This and the three succeeding paragraphs are taken from “ Animal 
Life and Intelligence,” p. 425. 
