During the conjugation of Paramecium tetraurelia, one meiotic nucleus which enters the paroral region survives and undergoes mitotic division to form gametic pronuclei, while the remaining seven degenerate.To clarify if these meiotic outcomes degenerate in an apoptotic way, two kinds of vital fluorescence dyes, acridine orange and Hoechst 33342 were used.The observation showed that the degenerating nuclei outside the paroral region stained yellow-orange or greenish which indicates a programmed nuclear degeneration.