ABSTRACTMethods for inducing selfing, and the relation between selfing and the life cycle ofEuplotes woodruffisyngen 3 are reported. Three intercrossing stocks were used in this experiment. Selfing was induced with several treatments as follows: cell‐free fluid from the cultures of complementary mating types; intact cells of GI or S phase in the cell cycle; heat‐killed cells, and lysed cells of GI‐, S‐, and D‐phase cells which were prepared by freeze‐thawing. Stock SJ‐27 was used as a parental stock from which Fl clones were originated through selfing. The other two stocks, SJ‐8 and SJ‐19, were used as testers. The period of immaturity varied from clone to clone. The heterotypic conjugation of clones with cells of stock SJ‐8 seems to occur earlier in the life cycle than with cells of stock SJ‐19. This result shows that this syngen has an adolescent period in the life cycle. The length of selfing immaturity seems to be different from that of crossing immaturity, and selfing appeared slightly later than crossing with testers. But the clones in which selfing 1st occurred are considered to be in adolescence or maturity, not in senility. Once selfing appeared in any clone, the clone continued to produce selfing pairs till just before clonal death. The viability of selfing and of outcrossing were compared and found not significantly different. Inbreeding depression took place in some of the F2 clones by successive selfing. The viability of F2 clones from young parents was significantly higher than that from old parents (220 to 230 fissions) both in selfing and outcrossing. The total life spans which were studied in three F1 clones wer