ACTIVATION AND INHIBITION: ORAL PRIMORDIUM 137 



sector bearing a mid-stage primordium is grafted onto a non- 

 differentiating stentor (without primordium and not in process of 

 regenerating, reorganizing, or dividing), the primordium is 

 promptly taken down and resorbed — not sloughed. Notice in 

 Fig. 34A that the patch itself is not resorbed, nor are the newly 

 multiplied fine striping to the right of the primordium site; 

 instead, the sector becomes part of the lateral striping of the host. 



This experiment shows that something besides cytoplasm and 

 macronucleus is necessary for regeneration. The cell must also be 

 in a state of activation. The nuclei of the non-differentiating host 

 could have been replaced by others from an actively regenerating 

 stentor and primordium resorption would still have taken place; 

 likewise if the host's primordium site had been replaced with the 

 grafted sector. Therefore the state of inhibition (or its opposite, 

 activation) seems to characterize the cytoplasm; and not merely 

 the part adjacent to anlage formation, but every part of the cyto- 

 plasm. For it is clear that an inhibiting influence was spreading 

 from the host, across the grafted patch, to the primordium, 

 resulting in its dissolution. There are indications, though not yet 

 conclusive, that the endoplasm as well as the macronucleus is 

 indifferent, with cell states characterizing the cortex alone. 



A reciprocal influence appears to occur in the later history of 

 this type of case; for now the grafted primordium site, lacking 

 subtending oral structures, is incited to produce a regeneration 

 primordium and brings the host along with it into activation, with 

 the result that combined regeneration and reorganization occur to 

 produce a doublet stentor. 



Rapidity and success of induced resorption depends upon the 

 stage of development of the imposed primordium. Early anlagen 

 to stage 3 can be completely resorbed within about 2 to 4 hours. 

 Stage-4 primordia which already have a well developed membran- 

 ellar band can also be dissolved, but this requires many hours 

 during which the anlagen crumples and is gradually taken down, 

 though complete resorption may not occur. From stage 5 onward, 

 the primordia do not seem to be resorbable under any conditions, 

 yet they do not remain unaffected when grafted to non- 

 differentiating hosts. Late primordia shrink in length or become 

 compacted and convoluted as if the ectoplasm were not co- 

 operating in their deployment, and mouthparts are not developed 



