488 C. M. Child 



begins to grow and develop. What line of differentiation will it 

 most naturally take ? Owing to the symbiotic relation existing 

 between the cells differentiation in the direction oi A will be most 

 favored as this secures it the advantages which A received. In 

 other words, this will be the direction of development along which 

 social pressure will tend to guide it. And the result will be a regen- 

 eration of the missing part" (Holmes '04, p. 282; '07, pp. 420, 



411)- 



In 1906 (Child '06a) I criticised this illustration on the ground 



that if the cells or parts were mutually dependent, i. e., if sym- 

 biotic relations existed between them, removal of any one of them, 

 e. g.. A, w^ould bring about changes in the others in consequence 

 of which their influence upon the undifferentiated cell substi- 



©:©:© 

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tuted for A would be different from what it was originally, and 

 hence the undifferentiated cell or part would develop — not into 

 another A but into something else. There is logically no escape 

 from this conclusion. The removal o^ A results in the formation 

 of a new system different from the original and must necessarily 

 do so, except under certain hmiting conditions to be discussed 

 below. 



Holmes' reply to my criticism is as follows: "According to 

 Child, since the removal of ^^ would alter 5, G, F^ etc., not only 

 something different would be developed in place of A, but the 

 whole complex, according to my theory, would be profoundly 

 altered. How far this tendency will result in a modification of 

 these cells depends on the plasticity of the organism and the degree 



