When conjugation is called an occasionally in paramecium (paramecia), but also in other ciliates observed (ciliates) sex operation, two of the single-celled another place in which, with their long sides to each other's genetic information exchange.
In both paramecia, the small nuclei ( micronuclei ) divide twice one after the other, i.e. meiotically , so that there are four haploid small nuclei in each cell . At the same time, the large nucleus ( macronucleus ) gradually decays . Of the four small nuclei formed in each cell, three are dissolved again and the fourth divides again. One part of the dumbbell-shaped dividing nucleus travels to the neighboring cell, where it merges with the division product of the nucleus there that has not migrated over. After exchanging the core material, the two adjacent individuals separate again. So there is no cell proliferation. The nucleus, which has now become diploid again in each paramecium, finally divides into a new small nucleus and a new large nucleus which becomes polyploid .