242 GRAND STRATEGY OF EVOLUTION 



in absorbtive area, in location, in fixation, and in mova- 

 bility of the 'visual organs, that a fitting architectural 

 response to these more specific demands is chiefly mani- 

 fest Hence, when the body is in its normal position, 

 whether its neural side is up or down, the windows of 

 the body are generally turned toward the chief sources 

 of light, or can be so turned, without rotating the body 

 on its longitudinal axis. But while the dimensions, 

 dioptric properties, and other attributes of the eyes 

 may readily change in response to the demands of the 





FIGURE n. DIAGRAM TO ILLUSTRATE THE FUNCTIONAL ORIENTATION OF THE 

 BALANCED TRIAXIAL SYSTEM OF VITAL ARCHITECTURE TO THE UNBALANCED 

 SYSTEM OF NATURE ARCHITECTURE. A, side view of an arachnid-like animal. 

 B, cross section of the same in region III, but with the paired eyes of 

 region I, and the paired trunk muscles of region V and VI projected onto 

 the same plane. Both figures are structurally oriented to the dominant 

 actors light, S, gravity G, and to the compass points of the great tangential 

 plane with its irregularly distributed minor actors. 



In B, the balanced effects of a luminous point at s*, are indicated and 

 the unbalanced effects when the point is shifted to /, J 1 and s*; I.e., and 

 r.e., right and left eyes; ap.m., paired appendicular muscles; ep.m., and 

 hp, epaxial and hypaxial trunk muscles (myotomes.) 



outer world, the inner ends of the optic nerves never 



change their relative points of attachment to the brain 



throughout the whole vertebrate and arthropod stock. 



But when the neuro-haemal axis is parallel with 



