CONCLUSIONS AND SUGGESTIONS 183 



in Harenactis (Fig. 82, p. 147) show that the radial 

 arrangement characteristic of the animals in nature is 

 not invariably determined in the protoplasm, but is 

 only one of various possibilities, which may or may not 

 be realized according to conditions. 



If my conception of the relation between the meta- 

 bolic gradient and dominance is correct, then of course 

 the origin of a new gradient is the origin of a new domi- 

 nance, and if such a gradient is uninhibited by gradients 

 in other directions, and if its metabolic rate is high 

 enough, it becomes the major axis of an individual and 

 its region of highest rate the dominant apical region. 



MORPHOLOGICAL DIFFERENTIATION IN RELATION TO 

 METABOLIC RATE 



The belief that qualitative differences of some sort 

 in the fundamental constitution of the organism must 

 underlie the morphological and physiological differences 

 which arise during development in different parts of 

 the individual has been so widespread among biologists 

 that any attempt at even a statement of the problem 

 of differentiation in anything like quantitative terms 

 is sure to meet with serious objection and criticism in 

 some quarters. Nevertheless, the simplest and most 

 satisfactory, and, I believe, the only adequate, interpre- 

 tation of the data of reconstitution which have been 

 discussed in preceding chapters is that the starting-point 

 of differentiation is in differences in metabolic rate. 

 The attempt to interpret these facts on any other basis 

 very soon becomes involved, either in the barren assump- 

 tions of the hypotheses which simply postulate an 

 invisible organization to account for a visible, or else 



