HIGHWAY OF ANIMAL EVOLUTION 249 



greater freedom of action, and greater freedom from 

 more profitably responsive structures. 



VI. Other Registers of Constructive Action; In- 

 stincts, Intelligence, Cultural Implements 



In addition to the triaxial organization essential to 

 this basic orientation and guidance, there must be some 

 internal means of modifying, or reversing tropic ac- 

 tion from positive to negative, and negative to posi- 

 tive, when a constructive stimulus is intensified to a 

 point where it becomes painful, or injurious, or de- 

 structive, or where it has fulfilled its purpose, and 

 thereby ceases, for the moment, to be constructive. 

 That is, conduct, like growth, must be constantly read- 

 justed to itself, and to that good and evil which changes 

 the more, the more active the organism is ; and it must 

 be rightly readjusted, otherwise freedom of movement 

 would not be more constructive than sitting still and 

 waiting for something to happen. 



We do not know how this is done, but we cannot 

 doubt it is done, as may be easily demonstrated in the 

 laboratory; and besides, all about us are the living wit- 

 nesses to its accomplishment. All, the more highly 

 organized animals, for example, invariably react con- 

 structively, or rightly, to gravity, and on the average 

 they react rightly to many of the countless minor in- 

 fluences to which they are subject. The register of 

 one is in the architectural plan of the whole organism 

 and in its constant orientation to gravity. 1 



1 See also the remarkable orientation of nerve fibres within the visual 

 rods of arthropod ocelli, in reference to the direction of the incoming rays 

 of light, and also in reference to three perpendicular planes. "A Basis for 

 a Theory of Color Vision." W. Patten, Am. Nat. Vol. 32, 1918. 



