590 KARL T. WATJGH 



ness over a very wide field. The most important thing for them is 

 a very wide field and the equal distribution of attention over 

 every part. Hence their eyes are prominent and destitute of a 

 central spot so that they see all parts with equal distinctness.'' 



III. KINAESTHETIC SENSATIONS, THE GUIDE TO MOVEMENT 



In the human being who is at all introspective, kinaesthetic 

 sensations often come into the focus of consciousness, but presum- 

 ably more often they do not. In the latter case, strictly speaking, 

 they are hardly to be called sensations. They exist merely as 

 neural modifications. Traces are retained within the nervous 

 structure in the form of facilitated transitions across the synapses, 

 or. of increased permeability of the neurones. These neural pro- 

 cesses operate in controlling the actions of the body without nec- 

 essarily involving consciousness at the time. Sometimes they 

 emerge into consciousness late, as when we become aware of having 

 had our limbs in a certain position and know that they are not 

 now in that position. Again we may have kinaesthetic images of 

 bodily actions we are about to perform. 



Our theory of the guiding sense in the mouse may be introduced 

 with an illustration from human psychology, the phenomenon of 

 alternating personalities. The normal person may do many things 

 of which he is wholly unconscious, e.g., he may lay an object in a 

 certain place and, after a while, search for it, entirely unconscious 

 of having put it anywhere himself. Later when another person- 

 ality is dominant, it may occur that the knowledge of the location 

 of the object is present to consciousness and there is no difficulty 

 whatever in finding it. The second personality remembers putting 

 it in the place in which it is found. This phenomenon may be 

 explained on the supposition that during the incumbency of the for- 

 mer personality, the kinaesthetic sensations from the movements 

 of the limbs are unable to emerge into the conscious field because 

 other psychical processes, viz., those to which the normal person 

 is attending, have control of the system of neurones whose excite- 

 ment is accompanied by consciousness. Association of the kinaes- 

 thetic sensations in question with the present perceptions is 



