BEHAVIOR AND FUNCTIONS OF THE NUCLEUS 295 



of nuclear nodes. This would explain Weisz's (1956) observation 

 that mid-division stentors grafted to non-dividers induce a 

 coalescence of the nuclei of both partners. Originally evolved for 

 the proper timing of nuclear clumping in division, this relationship 

 between cytoplasmic and nuclear states would also be effective in 

 producing a usually superfluous clumping during reorganization 

 and regeneration because the state of activation always accom- 

 panies primordium formation. On this hypothesis the nucleus 

 would fail to clump in dividers from which early-stage primordia 

 were excised or caused to resorb, not because the primordium is 

 missing as a stimulus to coalescence, but because the cytoplasm 

 again came under the inhibitive dominance of the intact feeding 

 organelles and the state of activation was aboHshed. 



How, then, is the nucleus guided in elongating and renodulating? 

 Does it divide autonomously? These problems have engaged the 

 attention of Noel de Terra (1959) whose preliminary findings 

 she kindly communicated. Apparently the cytoplasm gives the cue 

 for elongation of the clumped nucleus, for if the compacted nucleus 

 of a divider was transferred to an interphase stentor no elongation 

 occurred. But if the condensed nucleus was transferred to a cell 

 with nucleus in the same condition, then the two nuclei elongated 

 together synchronously. Supportive are experiments already 

 described, indicating that if the nucleus is prevented from renodu- 

 lating at the close of division because of injuries suffered during its 

 compacted stage, then it remains as a rod in the interphase cell and 

 does not nodulate until the animal passes through another episode 

 of activation or redifferentiation (see Fig. 80c). 



De Terra is also finding evidence that the macronucleus in 

 Stentor is generally incapable of autonomous division and therefore 

 has to be pinched in two at the rod stage by the division furrow, 

 though autonomous division of macronuclear anlagen occurs during 

 conjugation. This correlates with the cytological picture when 

 separation of daughter cells is prevented by injury to late dividers, 

 the compacted nucleus elongating and renodulating as a single 

 chain instead of two. When she caused stentors to divide very 

 unequally, the macronucleus was also unequally and propor- 

 tionately distributed to the daughter products, quite as if the 

 furrow cuts through the rod nucleus wherever it happens to strike. 

 Likewise, when the clumped nucleus of a reorganizer, not normally 



