ACTIVATION AND INHIBITION: ORAL PRIMORDIUM 143 



now overtakes the reorganizer, and as the original primordium 

 goes into its final development the induced anlagen is resorbed 

 (see Fig. 38E). Stage-5 regenerators are no longer able to induce 

 reorganization in a partner cell. Therefore we may say that as 

 anlage development goes to completion the state of activation 

 ceases and is replaced by a state of inhibition. 



When does activation begin? This time can be determined by 

 several tests. If a sector bearing the primordium of a regenerator 

 is grafted into a regenerating stentor the transplanted anlage 

 continues its development along with that of the host; but if the 

 primordium is grafted into a regenerator in which the primordium 

 has not yet appeared, the transplanted anlage is resorbed. When 

 regeneration is induced by causing the membranellar band to be 

 shed in salt solutions and when some of the salt is carried over 

 with the specimen and regeneration is thereby much delayed, such 

 cells are also not able to support primordia grafted to them 

 although it may have been many hours since the stimulus to 

 regenerate was given. And if stage-2 or 3 primordia are implanted 

 on non-differentiating cells whose heads or mouthparts are then 

 excised, the stimulus to regeneration in the host is not itself 

 sufficient to support the primordium development and the anlage 

 remains for a long time in arrested development or may even 

 become partially resorbed, but is finally revived and continues 

 differentiation as the host primordium itself appears and develops. 

 Considering these results and allowing for an appreciable time-lag 

 in the effects upon each other of host and graft, we can conclude 

 that activation is not developed to an effective state until shortly 

 before the primordium appears. 



3. Relation of the macronucleus to activation and inhibition 



The cell states relating to primordium formation and develop- 

 ment seem to reside in the cytoplasm and are possibly restricted 

 to the cortical layer or ectoplasm. The nuclei probably respond 

 to changes in the cell state, as when macronuclear nodes condense 

 and micronuclei undergo mitosis simultaneous with the passing 

 of the cell from its state of activation to one of inhibition ; but they 

 do not seem to be the bearers or determiners of these cell states. 

 The evidence for this is, briefly, that enucleated non-differentiating 

 stentors cause as prompt and as complete a resorption of anlage in 



