102 THE BIOLOGY OF STENTOR 



grafted doublet and triplet stentors does the frontal field and 

 membranellar band become much enlarged over the normal, as if 

 the excessive girth of these complexes could support a larger 

 structure. It seems clear that reorganization is not an essential 

 growth process, for otherwise it should occur with great regularity. 

 Considering only the opisthe, a daughter cell starts with a set of 

 feeding organelles which appears to be proportionate to the cell 

 volume and therefore about half the size of those of the parent 

 cell. If the membranellar band can increase only by adding new 

 membranelles through primordium formation, reorganization 

 should occur always before the next division and probably at a 

 certain time when disproportion sets up a tension. But re- 

 organization does not occur with regularity and, ever since 

 Balbiani, it has been observed that stentors of any size can be 

 found reorganizing. This includes even very tiny individuals, 

 which I can vouch for, as well as animals in which the oral struc- 

 tures do not appear in any way disproportionate to the cell size. 



(e) Need for adjustment of nuclear dimensions ? 



Although Balbiani did not find an increase in the number of 

 macronuclear nodes following reorganization, Johnson reported 

 that this was usually the case. Of i8 reorganizers, he found that 14 

 increased the number of macronuclear nodes, 2 remained 

 unchanged in this respect, and 2 even decreased the number of 

 nodes. The increase was sometimes to twice the original number 

 of nuclear beads, but the new ones seemed to be smaller. Therefore 

 he suggested that reorganization is for the purpose of increasing 

 the active surface but not the size of the macronucleus, or that 

 the surface-volume relation is adjusted as required, even in the 

 direction of decrease. I may mention here that I have also observed 

 cases of decrease in nodal number following reorganization of 

 regenerated stentor fragments that contained too much nuclear 

 material. 



A striking demonstration of this correlation between nuclear 

 size and reorganization was given by Schwartz when he showed 

 that reorganization could be induced at will by cutting out most 

 of the nuclear beads. Weisz (1951a) and I have confirmed this. 

 When only one or two nodes were left, they at first enlarged the 

 surface by becoming spindle shaped, just as Prowazek (1904) 



