The nuclear reorganization pathway of Paramecium during conjugation was investigated for 12 morphospecies. For P. woodruffi and P. schewakoffi the nuclear reorganization was studied for the first time. Several key elements of the process were chosen for the analysis, including "crescent" or "parachute" stage of the micronucleus, number of nuclear products and time of their degradation, and behavior of the old macronucleus. The carried out analysis allowed making dendrogram and topogram of the nuclear reorganization similarity (UPGMA) of the investigated species. The constructed tree did not coincide with the results of our previous molecular-biological analysis in several ways. According to SSrRNA gene sequences, the basal branching pattern of P. bursaria and P. duboscqui is congruent with some peculiarities of their nuclear reorganization. As an ancient species, they diverged from each other and from P. putrinum quite long ago. It seems, the taxonomic species with shorter immaturity period and outbreeding strategy (P. putrinum) could show faster evolution rate. For the nuclear reorganization of that species and, probably, for it's mating type system we can expect secondarily modification. General direction of evolution for the old macronucleus changing in Paramecium is going, apparently, from the absence of any changing to the macronuclear fragmentation at the earlier nuclear reorganization steps.
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