144 '^"E BIOLOGY OF STENTOR 



nucleated primordium sectors grafted to them as nucleated hosts, 

 and the macronuclear nodes of an early regenerator can be 

 replaced by those of a non-differentiating cell without stopping 

 the course of regeneration (unpublished). In the latter experiment 

 "non-regenerator" nucleus clumps and renodulates on cue just 

 as the original nucleus would have done. It therefore appears that 

 the nucleus simply responds to any demands made upon it by the 

 cytoplasm without taking the lead in cell redifferentiation, though 

 of course the macronucleus is essential to primordium formation. 

 Yet the presence of the macronucleus seems to be necessary for 

 achieving a state of activation in the cytoplasm, as suggested by 

 the following experiment. Both feeding organelles and macro- 

 nuclei were removed from coeruleus and after five hours re- 

 generation primordium sectors were grafted to them. Normally 

 the hosts would have been in active regeneration by this time but 

 now, lacking the nucleus, they behaved exactly like non- 

 differentiating hosts, causing resorption of the grafted anlage. It 

 follows that the nucleus is not only very probably essential to 

 protein synthesis in the elaboration of the oral primordium but is 

 also necessary for the achievement of the postulated state of 

 activation in the cytoplasm. Another finding which points to the 

 same conclusion is that if regenerators with early primordia are 

 enucleated the anlage are then soon resorbed. Not only is there no 

 further synthesis of ciliary proteins, or whatever is involved in the 

 further development of the primordium ; the developing organelles, 

 in contrast to remnants of those already formed, are actually 

 taken down and resorbed, so that it appears that the nucleus is 

 necessary for the maintenance as well as the achievement of the 

 state of activation. 



4. Relation of intact feeding organelles to activation 

 and inhibition 



Because removal of all or of a substantial portion of the feeding 

 organelles initiates their complete regeneration, it is natural to 

 suppose that the formed parts had exerted an inhibition on the 

 production of their like. Indeed, it is clear from the experiments 

 recounted above that non-differentiating stentors are continually 

 inhibiting primordium formation because they even cause 

 resorption of already well-formed anlagen grafted on them. This 



