BEHAVIOR AND FUNCTIONS OF THE NUCLEUS 281 



incapable, without the stimulation accompanying the process of 

 conjugation, of regenerating the macronucleus. This result is 

 fortunate indeed, permitting us to neglect the micronuclei which 

 cannot be seen in the living animal and would be most difficult to 

 work with. Schwartz's demonstration of the ineffectiveness of the 

 micronuclei must have been confirmed many times in the study 

 of emacronucleate stentors; for although most of the adhering 

 micronuclei are no doubt removed with the macronucleus, a few 

 scattered ones probably remain, yet these specimens never 

 regenerate nor long survive. In what follows we shall therefore be 

 concerned only with the macronucleus, designating it as such or 

 simply by the word nucleus. 



I. Location of the macronucleus 



In small species of Stentor, such as igneus and multiformis , the 

 nucleus is a single ovoid mass near the center of the cell ; but in 

 forms like coeriileus and polymorphus, which are about a hundred 

 times larger, the nucleus consists of many parts or nodes in linear 

 sequence within a common nuclear membrane. In between, there 

 is roeseli with an elongated, nodulated nucleus and niger which is 

 about the same size but has the compact nucleus. It may be 

 significant that nodulation after division is delayed in roeseli 

 (Johnson, 1893) so that for a considerable time the nucleus has a 

 rod shape, which might be considered a transition form. The 

 species niger is conspicuously slow and lackadaisical in its swim- 

 ming movements. Phylogenetically this suggests that the former is 

 on the way to developing a moniliform nucleus out of one which is 

 rod shaped and arose by elongation of the compact form, as well 

 as that the latter is pushing the cell size as far as it can go on a 

 compact nucleus whose surface area of interaction with the cyto- 

 plasm is minimal with reference to the volume of nuclear material. 

 The chain nucleus of a form like coeriileus of course passes through 

 rod and spheroid phases during division and other times when 

 there is oral primordium formation. These changes in form led 

 Johnson to the conjecture that ontogeny is here repeating a 

 phylogeny in which the compact form of the nucleus can be 

 assumed to be the most primitive. 



We shall confine our discussion to the well-studied chain nucleus 

 of coeruleus, but this description will serve fairly well for all species 



