SENSES, INSTINCTS, AND INTELLIGENCE 333 



which cover the facts as simply, as shortly, and as consis- 

 tently as possible. When the formula " reflex action " 

 suffices satisfactorily, there is no need to complicate matters 

 by reference to " latent mentality," though other reasons 

 may lead us to this postulate. At a certain level in animal 

 behaviour we find it impossible to give an adequate descrip- 

 tion without using psychological terms, like awareness, 

 perception, judgment ; and then we are justified in speaking 

 of, let us say, the bird's mind. What the bird's mind may 

 be in relation to the bird's nervous system, what the bird's 

 thinking may be in relation to the bird's metabolism, is the 

 most difficult of all questions — probably because we have 

 not learned to put it rightly. We are evading this question 

 here by assuming that the psychological and the physiological, 

 the mental and the metabolic, are correlated aspects of one 

 reality — the life of the creature. At one time it is most 

 prominently a body-MiND (bio-psychosis) ; at another time 

 it is most prominently a mind-BODY (psycho-biosis) ; perhaps 

 it is always both. At the lower end of the inclined plane 

 the psychical aspect is often, for practical purposes, negli- 

 gible. At the upper end the psychical aspect is predominant. 

 The double lines of the diagram express this two-aspect 

 theory. 



(i) In very simple organisms we see reactions to changes 

 in the surroundings, e.g. encystment when drought sets 

 in. We also see almost explosive liberations of stores of 

 potential chemical energy, as in the sudden protrusion of 

 a long thread of protoplasm. Perhaps the same primitive 

 activity may be seen in the embryonic cells of higher 

 animals. 



(2) A step higher brings us to fixed reactions, uniform 

 answers which are given to a variety of environmental 

 questions. They are doubtless the outcome of the selection 

 of the relatively fitter responses. Thus the Slipper Animal- 

 cule (Paramcecium) reverses its cilia, backs away from an 

 obnoxious stimulus, turns slightly on its own axis, and goes 

 forward again. This is its fixed reaction — the answer it 

 gives to practically every question. On the other side 



