370 THE BIOLOGY OF STENTOR 



intact for a whole week and undergo dissolution only just before 

 the death of the specimen at which time the appearance of a general 

 necrosis could just as well account for structural disintegration. I 

 have observed nothing like an intimate nutritive relationship 

 between the nucleus and the feeding organelles such that removal 

 of the nucleus withdraws their maintenance and results in the 

 prompt resorption of specialized organelles. In fact, the failure of 

 excised heads to reduce the feeding organelles to a size propor- 

 tionate to the small fragment, if enucleate, indicates just the 

 opposite : that the nucleus is necessary for the resorption of formed 

 organelles. Nor is there any substantiation that the hypothetical 

 metabolites are present in limited quantity. Arguing against this 

 assumption is the fact that grafted pairs of stentor produce one, 

 two, or three primordia and sets of feeding organelles regardless 

 of the amount of nuclear material present; and grafting of an 

 enucleated stentor to a normal animal may lead to the production 

 of a doublet just as readily as when both nuclei are present 

 (Tartar, 1954). Similarly, if the fine-line zone of a stentor is split 

 by an enucleated meridional patch of wide striping, three anlagen 

 of normal size are usually formed instead of one (Tartar, 1956a). 

 On Weisz's hypothesis this would imply that the single animal is 

 quite able to produce three "quanta" of oral metabolites. If so, 

 there is no reason to suppose that an intact set of feeding organelles 

 would monopolize them and in this way exert inhibitive action on 

 the primordium site. The additional postulate — that the kineto- 

 somes act back on the nucleus to produce internodal differences — 

 was also not confirmed; for in later tests all sections of the 

 macronucleus were found to be equivalent (Tartar, 1957b). 



Form in ciliates is still without satisfactory causal analysis; but 

 this is no wonder since no adequate theory of morphogenesis of 

 any organism has yet been achieved. In this perspective, the 

 progress with ciliate protozoa appears promising and we may ask 

 how, if eventually successful, a verifiable explanation of their 

 development might be pertinent to general problems of 

 cytodilferentiation. 



3. Stentors and cells 



First we shall consider whether a ciliate like Stentor is a cell, or 

 properly should be included in the class of those things called cells, 



