156 THE BIOLOGY OF STENTOR 



and this was confirmed by Hetherington (1932b). When mid-stage 

 dividers were greatly disturbed by cutting and spreading them out 

 in a clover-leaf pattern, the separated parts then healed together 

 and the primordium continued to develop, but almost all of the 

 specimens reorganized instead of dividing (Tartar, 1958c). 

 Division was usually only thereby postponed, and successful 

 fission with a new primordium generally occurred some time later. 

 Likewise, when heads of early dividers were circumscribed and 

 rotated 180° on the body, there occurred an initial partial regression 

 of the division primordia, probably due to the cutting injury as 

 such, after which the anlagen continued developing but moved 

 forward instead of posteriorly and the animals reorganized instead 

 of dividing. In three cases a stage-3 divider was grafted to a small 

 non-differentiating stentor or to the oral longitudinal half of such 

 an animal. The primordium served only to replace the feeding 

 organelles of the divider and, surprisingly enough, the mouthparts 

 of the partner were also gradually resorbed though there were 

 none to take its place (Fig. 39c). When early dividers were grafted 

 to regenerators, regeneration proceeded on one side while re- 

 organization instead of division occurred on the other as already 

 mentioned in connection with dividers failing to induce division. 

 Even when two stage-3 dividers were grafted together in homo- 

 polar parabiosis they reorganized doubly instead of dividing. It is 

 clear that furrow formation is not determined from the beginning 

 of the division process but is inaugurated much later, so that shifts 

 from division to reorganization are possible. 



Likewise dividers can easily be changed into regenerators. 

 Causin had at least one case in which he cut off the anterior right 

 hand corner with membranelles of an early dividing coeruleus the 

 primordium of which then served for regeneration instead of 

 division. When primordium sectors were cut and isolated from 

 dividing animals, these pieces made no attempt to divide but 

 used the anlagen to regenerate the missing ingestive organelles 

 (Tartar, 1958c). It was also shown that if the head or feeding 

 organelles are excised from dividing cells they then regenerated 

 instead, postponed fission with the formation of a new division 

 primordium usually occurring sometime later. In conclusion it 

 may be said that in their beginning phases fission, reorganization, 

 and regeneration are more similar than different, so that a stentor 



