106 The Unity of the Organism 



the time at which growth is half completed." 3 



Assuming that the growth of an amphioxus, lot us say, to 

 adulthood represents a growth cycle of this statement, that 

 the production of somites begins with the most anterior one 

 and proceeds toward the tail, and that the successive growth- 

 increments (corresponding to x in the formula) arc regis- 

 tered in the somites as we find them, then the animal's body 

 as exhibited by its myomeres would correspond fairly well 

 to Robertson's statement under (1), as would several of the 

 other growth series we have glanced at, and as would also 

 great numbers of series presented by ordinary plants and 

 animals. 



The formula for growth contained in (2) is, according 

 to Robertson, "such as would be expected to hold good were 

 growth the expression of an autocatalytic chemical reac- 

 tion." Assuming the general correctness of these state- 

 ments, no one interested in the larger problems of organic 

 growth could hesitate to believe that they must be impor- 

 tant in some way. 



However, that the relations shown do not prove that au- 

 tocatalytic chemical activity is a cause of growth in any- 

 thing more than a subordinate, contributory way, is obvious 

 on reflection". In the first place, Robertson himself has 

 pointed out, in substance, that such action says nothing 

 about the particular shape which the mass of transformed 

 substance takes, but since some characteristic configuration 

 or shape is fundamental to all organic growth, the entities 

 for which A and x stand in the formula are really only ab- 

 stractions. Although the formula may apply approximately 

 to a great many organisms, it will apply to none exactly, 

 except by chance to a very occasional one. This is the gen- 

 eral form of criticism, illustrations of which are seen in the 

 fact that in the series of direct and inverse gradients shown 

 in the vetch (figure 59) and Cassia (figure 60), respectively, 

 the formula appears not to apply at all. The general pur- 



