38 INDIVIDUALITY IN ORGANISMS 



less rapid and less intense than that of a, and, as 

 indicated in Fig. 2, the transmitted change will be 

 weaker, perhaps less rapid, and its limit of effectiveness 

 less than that arising from a. The influence of the 

 region b must then be less than that of a in determining 

 the metabolic rate in other regions and a remains the 

 dominant region. 



FIG. 2. Diagram illustrating origin of major and minor gradients in 

 a simple case: a, apical region of major gradient; b, apical region of 

 minor gradient. 



If, however, the region b or any other region is suffi- 

 ciently intensely or sufficiently often locally excited 

 independently of a, a persistent gradient may arise with 

 relation to b without destroying that related to a. In 

 such a case two dominant regions, a and 6, exist, but a 

 may still dominate b to a greater or less extent unless 

 the reactive capacity or irritability of b becomes equal 



