ACTIVATION AND INHIBITION: ORAL PRIMORDIUM 141 



the next section, the stage of differentiation of the anlage is 

 probably significant as marking the waxing and waning of a w^ave 

 of activation. That this activation or the reciprocal state of 

 inhibition characterizes some aspect of the whole cell is shown by 

 the importance of the relative size of the two graft components. 

 A large regenerator induces reorganization in a much smaller non- 

 differentiating partner, if the latter is larger it forces the regenerator 

 to back down and resorb its primordium. If the two cells are equal, 

 anlage resorption also occurs, and this seems to indicate that the 

 force of inhibition is stronger than that of activation. However 

 that may be, the two forces or cell states are seen to be quantitative 

 and potentially measurable. 



On the other hand, the stimulus which starts the whole course 

 of regeneration is stronger than the forces of inhibition, as indeed 

 it must be if primordium formation is to be possible at all. Thus 



A. Induced reorganization, a: Large stage-3 regenerator 

 (activated) grafted to small non-differentiating partner (inhibited 

 with respect to anlage formation), b: Initial partial regression 

 of the primordium under influence of partner, c: Revival of 

 regeneration primordium and induction of reorganization 

 primordium in small partner, d: Regeneration-reorganization, 

 with resorption and renewal of oral structures in the reorganizer, 



producing a doublet stentor. 



B. a: Stage-4 regenerator grafted to small non-differentiating 

 partner, b: More advanced regeneration primordium does not 

 suffer partial regression and a reorganization anlage is induced 

 so rapidly that no concomitant stripe multiplication occurs 

 {y, cf. x). c, d: Regeneration-reorganization produces a doublet. 



C. a: Stage-o regenerator (stripes splitting in primordium 

 site) grafted to small non-differentiating cell — immediately 

 following operation to show how cells are split down the backs 

 opened out and pressed together, b: Regenerator continues to 

 stage 2, induced primordium in stage i (predominance of activa- 

 tion), c: Conspicuous regression of both anlagen (predominance 

 of inhibition), d: Revival of primordia leading to doublet 

 formation through regeneration on one side and reorganization 



on the other. 



D. Abortive primordium development, a; Stage-4 regenera- 

 tor grafted to non-differentiating animal of same or larger size. 

 b, c: No induction. Advanced primordium arrested, shortened, 

 crumpled — neither developing nor resorbing and showing no 

 normal membranelles. d: Simultaneous regeneration and 



reorganization occurring much later. 



