122 ANIMAL BEHAVIOUR 



head (when, however, muscular movement is again the origin 

 of the intuition). Doubtless there is space-intuition from the 

 actual or virtual movements that occur during the reception of 

 stimuli by the internal ear (the " labyrinth ") and the consequent 

 stimulation of the cerebellum, which controls the " tonus " or 

 normal tension of the skeletal muscles. There is obscure space- 

 intuition (" direction ") when a man, lying prone on a turntable 

 that can be rotated with negligible friction, and with exclusion 

 of visual and auditory stimuli, can roughly estimate the angle 

 through which his body is turned. Here there is consciousness 

 {via the muscle and articular receptors) of the inertia of the 

 body. 



Mainly space-intuition comes from consciousness of the activi- 

 ties of the eye-ball muscles. [It is extraordinary that these six 

 pairs of muscles, each pair representing a nervous segment, are 

 about the most constant of all morphological characters of the 

 craniate vertebrata.] In all space-intuitions there are minute and 

 most delicate motions of these muscles. The estimate of the 

 length of a line up and down or side to side comes from the 

 movement of the optical axes set up by the eye muscles. The 

 estimate of the area of a circle or other figure comes from the 

 movements of the optical axes round the periphery. Distance 

 in the direction right-ahead comes from the varying inclination 

 given to the two optical axes and probably also from the move- 

 ments of the muscles of accommodation that are instrurnental 

 in focussing the eyes. And so on. Visual space-intuition is to 

 be completely described in terms of the consciousness of the 

 activities of the ocular muscles. 



The '* field of space " that we intuite directly from natural, 

 unassisted bodily muscular activities is small. A man may only 

 move his body, by walking, through (say) 30 miles in a day. He 

 might walk across a continent and then (conceivably) swim an 

 ocean and so attain intuition of the spatial magnitude of the earth, 

 in a few years. He may only see round about him for a few 

 miles. He may appreciate the angle subtended by a sixpenny- 

 piece if it is only a few yards distant. But the artifacts which 

 man uses enormously increase his visual field so that space comes 

 to be represented in " light-years," when man reaches out into 

 the cosmos. But here again the intuition of these greater spaces 



