 Although the "Tubifex" worms are hermaphrodites, the male and female organs become mature at different times; thus self-fertilization is avoided, and cross-fertilization is encouraged.Two mature "Tubifex" worms undergo copulation by joining ventral and anterior surfaces together with their anterior ends pointing opposite directions.Thus, the spermathecal opening of each worm is nearer to the male apertures of another worm.