EVOLUTION OF INTELLIGENCE. 117 



This cumulation of the effects of previous responses, 

 this formation of internal stimuli reacting on the be- 

 haviour is, of course, no new factor in the development 

 of organisms (p. 56). It is the epigenetic factor, the 

 means of differentiation in the ontogeny of the individual. 

 Thus an organism will respond differently according as it 

 is starved or well-fed. The storage of nutriment in the 

 tissues of a plant provides an internal stimulus affecting 

 its response ; so a hungry animal will behave differently 

 from one that is satiated. In fact, the whole behaviour 

 of an organism is determined by the condition of the 

 mechanism at the time the stimulus is received, and this 

 again depends on the responses previously called forth. 

 It should never be forgotten x that an organism reacts as 

 a whole, each response being closely or remotely related 

 to every other and to the entire organisation of the 

 organism. 



Intelligent behaviour, from the physiological point of 

 view, is prompted by indirect responses. Influences are 

 brought to bear on the course of metabolic changes 

 diverting them in this or that direction, in a manner 

 which cannot be foreseen by an outside observer who is 

 not acquainted with the entire past history of the animal. 

 The final response may then appear to be spontaneous, 

 and even unrelated to the initial stimulus. The influences 

 above mentioned are, besides the external stimuli or 

 factors of the environment, either due to the transmitted 

 factors of the inheritance or the internal stimuli caused 

 by the lasting effects of previous responses. 



Lastly, we are still in the dark as regards the evolution 

 of consciousness, the highest stage in the development of 

 the mental processes, for our knowledge of the ana- 

 tomical structure and physico-chemical processes which 

 accompany it is still too incomplete to enable us to de- 

 termine when it first made its appearance in the animal 

 series. We can tell approximately at what stage in the 

 ontogeny of individuals of our own species consciousness 



