HIGHWAY OF ANIMAL EVOLUTION 245 



surface of the body, or located on radial axes. But if 

 we bear in mind the necessary correlation between 

 vision and precisely regulated locomotion, we can read- 

 ily see why, with evolution, there has been a progres- 

 sive reduction in the number of eyes, while an exact 

 right and left symmetry in the one remaining pair is 

 persistently retained. In exact locomotor reactions to 

 light, it is apparently essential to establish a point for 

 point correspondence, right and left, between the outer 

 world and the internal system of response. This re- 

 sult can be obtained with one pair of symmetrical 

 image forming visual organs, but not with several pairs, 

 nor with asymmetrically, or radially, distributed or- 

 gans (Fig. 3). 



Thus when animals built on the triaxial plan are 

 normally oriented to the outer world of action, the 

 body, like a weather-vane, is always impaled on some 

 one of the vertical lines of gravity; but it is relatively 

 free to turn its face toward any actor on the horizon, 

 and to move like an arrow, head-first into the winds of 

 circumstance. 



We can now, perhaps, see more clearly the neces- 

 sary correlation between vital architectural plans and 

 world architecture. For any animal built on this 

 structural plan, in order to be in its most effective po- 

 sition for purposeful action, must have its two major 

 axes of organization, neuro-hsmal, right and left, 

 rightly oriented to the two major axes, radial and tan- 

 gential, of terrestrial organization. We can also see 

 that this triple polarization of the triaxial vital system 

 is nothing more or less than the expression, in archi- 

 tectural terms, of a threefold qualification of life's free- 

 dom of movement (radial, tangential, and compass 



