CHAPTER XVI 



BEHAVIOR AND FUNCTIONS 

 OF THE NUCLEUS 



Stentors have two kinds of nuclei, yet the nuclear story can be 

 simplified because the role of the micronuclei may be stated 

 briefly. On some signal from the cytoplasm during fission they 

 divide and reproduce themselves by typical ciliate endomitosis. 

 This also occurs during the related cycles of reorganization and 

 regeneration, in which the cytoplasm is similarly activated to oral 

 primordium formation. Although multiplication in these two 

 processes may be meaningless, that during fission obviously 

 assures the continued presence of micronuclei, available for their 

 single known function, namely, to produce a new macronucleus 

 after sexual reproduction or conjugation. In this, their performance 

 is indeed complex and will be described in the following chapter. 

 But for the vegetative life of stentors the micronuclei are 

 demonstrably without significance. In a few ciliates bearmg a 

 single, non- vesiculate, ''massive type" micronucleus the situation 

 may be otherwise. By massive type is meant that the micronucleus 

 is relatively large and appears on staining to have a consistency 

 much like that of the macronucleus. Thus in Ur onychia transfuga 

 (Calkins, 1911a), Euplotes patella (Taylor and Farber, 1924; 

 Reynolds, 1932), and in Paramecium caudatum and bursaria 

 (Schwartz, 1934, 1947; Tartar, 1940), excision of the single 

 micronucleus is immediately felt and manifests itself in defective 

 regeneration or reduced rate of fission, though later adjustments 

 may correct these deficiencies. But in Stentor coeruleus which has 

 numerous vesiculate micronuclei, a careful study by Schwartz 

 (1934, 1935) has shown that the micronuclei may be entirely 

 removed without any appreciable effect on the macronucleated 

 cell; and conversely, that, as in Bursaria according to Schmahl 

 (1926), in the absence of the macronucleus micronuclei which are 

 present are not only unable to carry on the life of the cell but are 



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