DEPENDENCE ON ASSOCIATION. 91 



each separate act in the series can occur without a 

 separate stimulus from beyond the local nervous 

 co-ordination which controls the whole series, — so 

 that, after the start, each separate act in the series 

 has a sufficient guiding stimulus in the action 

 immediately preceding. There are many perform- 

 ances where the stimulus of the preceding action 

 is necessary for all but the initial action of the 

 series. In a performance involving a series of 

 associated actions, the performer often finds it im- 

 possible to start in the middle of the series and go 

 on to the finish, but must start at the beginning 

 in order to have for each action the guiding stimulus 

 of the preceding action. This is true of players 

 of musical instruments in certain musical passages 

 which are peculiarly difficult of execution. Other 

 performances of manual skill may have the individ- 

 ual movements so firmly associated that they can 

 not be performed properly when separated. Such 

 strength of association seems to have~ its counter- 

 part in the nest-building instinct of birds. These, 

 when they find a nest already half-built, do not 

 undertake to finish it, but instead they start a new 

 nest on top of it ; or else they tear it down and 

 then start a new nest from the beginning. In the 

 same way they frequently tear down their own 

 half-built work, or sometimes build a second nest 



