lOO THE BIOLOGY OF STENTOR 



about by changes in the medium, not necessarily unfavorable, 

 such as transfer from old to fresh culture fluid. It may be that 

 reorganization is a response to disproportionality of cell parts (see 

 below) and that under the most uniform conditions growth in all 

 parts proceeds so harmoniously that no disproportion arises. But 

 Hetherington's argument is vitiated by several contradictions. 

 First, he says that no physiological regeneration occurs in stentors. 

 Then he admits that he did find *'reorganizers" in unchanged 

 stock cultures of coeruleus. To explain this, he asserted that such 

 animals were regenerating from cryptic injuries; and he stated 

 that renewal of mouthparts is not the same as reorganization though 

 he did not offer a different definition. He said that his animals 

 were invaded by bacilli from which they were freed by repeated 

 transfers into new medium, during which reorganizations were 

 frequent; but then it might be held that the infection was really 

 the cause of reorganization. Hetherington's contribution, then, 

 was to direct attention to changes in the culture medium as a 

 possible cause of reorganization; and to raise, if not resolve, the 

 question whether replacement of worn out or injured mouthparts 

 should not properly be called regeneration, as reasonably as when 

 excisions are the inducement. 



That '* depression " conditions in the culture may be the cause 

 of reorganization, though not the only or principal one, was also 

 suggested by Balbiani (1891a), and Weisz (1949a) assumed the 

 same; but Causin (1931) found that unfavorable conditions never 

 seemed to cause reorganization. Merely adding new water to the 

 cultures was said to bring about reorganization (Weisz, 1949a). 

 Yet it is difficult to see how such a mild stimulation as change in 

 the medium could elicit reorganization when the most severe 

 cutting injuries involved in many stentor experiments do not. 

 I therefore also question Causin's (1931) remark that if the tailpole 

 is cut off a stentor the cell then undergoes a partial reorganization 

 as if in response to a mild injury. He did not describe what 

 happened beyond saying that the nucleus did not clump together 

 completely. 



Stentors in small drops under cover slips are incited to divide as 

 well as to reorganize, according to Balbiani (1891a), but this cer- 

 tainly does not occur with regularity in depression slides. I 

 reported (Tartar, 1958c) that a dilute solution of methyl cellulose 



