438 CM. CHILD 



metabolism in the anterior region is to a greater degree independ- 

 ent of conditions in other parts of the body and so is but little 

 altered when conducting paths are cut. The rate of metabolism 

 in the posterior region on the other hand, must be in high degree 

 dependent upon its connection with other regions, for when this 

 connection is severed the stimulation of conducting paths increases 

 its rate very greatly. The more anterior levels of the body are 

 largely independent of the posterior while the more posterior 

 levels are largely dependent upon the anterior. The degree of 

 independence or subordination of a body-region then depends 

 upon its level in the body. 



There is thus an axial gradient in degree of stimulation result- 

 ing from section with its lowest point at the anterior and its 

 highest point at the posterior end and this is evidently the expres- 

 sion of a gradient in degree of subordination. 



That these gradients are expressions of the axial gradient in 

 rate of metabolism described in the preceding paper (Child '13 a) 

 cannot be doubted. It was pointed out in that paper that the 

 region of highest metabolic rate in a living cell or cell aggregate 

 must be much more independent of other regions than they are 

 of it and so must inevitably dominate other parts to a greater 

 or less extent and within a greater or less distance from it. In 

 Planaria where a simple axial gradient in rate from the head 

 posteriorly exists the head is unquestionably the dominant region. 

 As regards functional relations this is self-evident but it is also 

 true at least for certain features of morphogenesis (Child '11 d). 

 As pointed out above, the stimulation gradient in pieces is merely 

 an expression under special conditions of the axial gradient and 

 of antero-posterior dominance. The increase in stimulation from 

 section with increasing distance from the anterior end means 

 simply increasing dependence upon stimuli coming from more 

 anterior regions. 



4- A remarkable relation between frequency of head formation 

 and degree of stimulation after section exists. The greater the in- 

 crease in rate of metabolism after section the less the frequency of 

 head-formation. 



