REGENERATION II5 



The Guttes assumed that both fragments regenerated. This is 

 true only insofar as the anterior fragments had to regenerate the 

 holdfast ; but this makes no demands on the nucleus and can even 

 occur in its absence. It has long been known (e.g., Morgan, 1901a) 

 that anterior halves need not and do not form an oral primordium. 

 Therefore the most important difference between the two types of 

 fragment is that oral anlagen formation occurs only in the posterior 

 ones, and this is somehow related to corresponding changes in 

 both macronuclei and micronuclei. 



To the Guttes, however, the only difference between the frag- 

 ments was that the posterior halves lacked the feeding organelles. 

 Their interpretation is accordingly highly questionable; for they 

 suggested that in the posterior halves the phosphoryolytic energy 

 utilized in membranellar beating could now be diverted toward 

 promoting mitosis. Historically, this explanation stems from the 

 Henneguy-Lenhossek hypothesis, 1898, of the homology between 

 mitotic centrioles and the fibrogenic basal bodies of flagella and 

 cilia. But the application cannot be valid if we accept Schwartz's 

 deduction (see p. 103) that mitosis also occurs during reorganization 

 of stentors, during which the original membranellar band is 

 retained and continues actively beating as the new one from the 

 reorganization anlage joins with it. Instead, it may be concluded 

 that regeneration, reorganization, and division are so similar that 

 each gives the cue for macronuclear and micronuclear increase; 

 and it may be the developing primordium which provides this 

 encitement, as in part suggested by Weisz (1951b).* 



3. Effective stimulus to regeneration 



That cutting injuries alone, without excision of parts, do not 

 result in regeneration or reorganization has been pointed out many 

 times. Morgan (1901a) tells how he cut the cell nearly in two 

 without effect, even if the cut passed through the membranellar 

 band. I have found, however, that if the feeding organelles are cut 

 in two and displaced, or if for any other reason a good set of mouth- 

 parts and a good membranellar band are present but not joined, 



* According to Uhlig (i960) " regeneration " can occur without primor- 

 dium formation, evidenced only by fusion and renodulation of the macro- 

 nucleus and formation of a new contractile vacuole under the wide-stripe 

 areas. Division also occurred without anlagen formation (cf. Fig. 18B). 



