212 GRAND STRATEGY OF EVOLUTION 



of differential growth, which we call the system of tri- 

 axial gradient increment, or briefly the triaxial system. 

 The progress of this growth system, in its main out- 

 lines, may be followed historically through the great 

 geological eras where each notable organic increment 

 is coincident with, or has its returns in, the appearance 

 of a new class of animals, and a new measure of vital 

 freedom. 



And today, in the embryos of all the higher animals 

 belonging to this system, we may see how they rapidly 

 retrace the same self-constructive ways, and repeat, one 

 by one, in due order, the main architectural innova- 

 tions which were chiefly characteristic of their ances- 

 tral classes. 



It is evident that a growth system which can con- 

 sistently produce such results as these must contain 

 within itself some constructive principle of great sig- 

 nificance, not found elsewhere in the organic or inor- 

 ganic world. 



In this chapter, we shall discuss this method of 

 growth and try to point out wherein this constructive 

 principle lies. 



I. The Triaxial System of Structural and Functional 



Gradients 



A constructive vital system, to attain the maximum 

 results, must be able to meet the increasing demands of 

 its own growth as they arise, and at the same time keep 

 in profitable conformity with the permanent demands 

 of the outer world. 



These demands from within and from without are 

 voiceless, it is true, but they are forever insistent, and 

 they must be fulfilled, if the system is to endure. 



