CHAPTER XVII 



TOWARD A GENETICS OF STENTOR 



The collaborative functions of nucleus and cytoplasm can further 

 be studied by artificial exchange of nuclei and cytoplasms between 

 different individuals and even different species of Stentor. Poten- 

 tially, natural exchange of traceable genetic material between 

 members of the same species through conjugation would comple- 

 ment such investigations. The circumstance common to both 

 approaches is that now we deal with qualitative alterations in either 

 the cytoplasmic or nuclear component, or both. 



I. Interspecific chimeras and nuclear transplantations 



New possibilities for experimentation appeared when it was 

 found that different species of Stentor could be fused together by 

 their cytoplasms in enduring unions, and that when foreign nuclei 

 are transplanted they are neither immediately ejected nor destroyed 

 but also persist, with the expectation of revealing interactions 

 between species-different nuclei and cytoplasms. Many combina- 

 tions are possible. The macronucleus can be removed and replaced 

 by that of a different species. Alien cytoplasm can be grafted so 

 that the host nucleus now operates w ithin a mixture of cytoplasms, 

 or nuclei alone can be added so that now a mixed nuclear comple- 

 ment works with cytoplasm almost entirely of one type. And 

 finally, relative amounts of the two types of nuclei and cytoplasms 

 can be mixed together in any desired combination. The parts of 

 three species could also be joined in similar permutations, but we 

 need first to work out the simpler combinations. In comparison 

 with the possibilities, the work which has so far been done (Tartar, 

 1953, 1956c) may be regarded as only exploratory. In fact, further 

 development of these studies was postponed until conditions 

 governing the states of activation and inhibition during primordium 

 formation, as well as the effects of altering the nuclear-cytoplasmic 

 ratio, and other points could be explored ; for all these factors have 



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