514 THE EVOLUTION OF MIND 



cise of intelligence. Dahl relates that when a spider is given 

 a fly that has been steeped in turpentine, it will not for a 

 time dart at another fly of that species. This is like simple 

 learning. 



(g) The improvement of the brain opened up a new pos- 

 sibility in the way of hereditary organisation that of in- 

 stinctive behaviour. In virtue of inborn nervous predispo- 

 sitions the animal seems to be from the first aware of the 

 significance of certain stimuli and configurations, and obeys 

 an impulsion to a definite routine which is singularly effec- 

 tive, though more or less independent of practice. Pure 

 instinctive behaviour is well illustrated by ants, bees, and 

 wasps; but there and elsewhere it may be mingled with 

 experimental, including intelligent, behaviour. Of instinctive 

 behaviour very perfect in its first performance many pictures 

 rise in the mind : the chick neatly removing the top of 

 the imprisoning egg-shell, the month-old kitten exhibiting 

 without imitation " almost a complete repertoire of move- 

 ments used by the adult cat in catching and killing mice ", 

 the young guinea-pig nibbling at a carrot at the end of the 

 first day after birth. In illustration of instinctive activities 

 that improve or change under various influences we may recall 

 the pecking of chicks and the singing of some birds. Of 

 the serial succession of steps in instinctive behaviour there 

 is no better illustration than the way in which the Yucca 

 moth on its first flight visits and pollinates the Yucca flowers 

 and lays eggs in the ovary. 



(h) The next level is that of intelligent behaviour, which 

 is characteristic of the higher reaches of the big-brained 

 line of evolution. It implies trial and error experimenta- 

 tion on subtler lines and more definite profiting by ex- 

 perience. Psychologists interpret it as implying ' perceptual 



