THE INHERITED IMPULSE. 143 



of growth activity. Now in this succession of 

 stimuli, suppose one of them to be dropped out 

 through some change in the environment, as pointed 

 out in Chapter V : the mere power of association 

 will remain sufficient to retain the corresponding 

 response in the chain of responsive activities. The 

 gap becomes bridged over ; and, though the stimuli 

 change within certain limits, the series of responses 

 remains the same for a time, though the change 

 in stimuli must eventually make its impression on 

 the chain of activities. Thus we see in the incipi- 

 ent organism an indwelling, potential energy which, 

 to some extent, independent of the environment, 

 impels the organism along that course of growth 

 which repetition has made customary to its race, 

 and thus determines the specific character of the 

 organism — whether it shall be dog or horse. 

 This, then, is that inherited impulse of growth 

 which, in combination with external forces, con- 

 stantly drives the organism forward on its course 

 of development, and, even while the environing 

 forces remain the same, is continually exposing 

 the developing individual to new stimuli, because 

 it is continually changing the individual. This 

 constant change in the stimuli which act upon an 

 organism is a point which cannot be too strongly 

 emphasised in our effort to imagine the immediate 



