The fourth trio of actresses to take over Eve Ensler's duties in The Vagina Monologues -- Shirley Knight, Andrea Martin, and popster Alanis Morissette -- begin their two-week stint March 21. The trio will remain until April 2.

Knight, a theatre veteran, most recently appeared on the New York stage in The Young Man from Atlanta. Martin won a Tony Award for the musical, My Favorite Year, and starred in her own one-person show, Nude, Nude, Totally Nude. Morissette is best known, of course, as a huge pop star. Among her songs are "You Oughta Know" and "Ironic." As an actress, she appeared as a silent, loopy God in Kevin Smith's "Dogma."

Eve Ensler's Vagina Monologues, starring Ensler herself, returned to New York the Westside Theatre Oct. 3, after previews from Sept. 21. Vagina reveals a series of different women's stories and experiences involving their genitalia. New introductions to the monologues have been written for the various threesomes, who will divide the text between them.

A large ad for the show in the Jan. 21 New York Times said "Beginning Feb. 8, three of the amazing women listed above will share the microphone at every performance. All these women will perform the monologues in the coming months." Among the listed actresses are such theatre vets, young and old, as Kathleen Chalfant, Elizabeth Franz, Mo Gaffney, Hazelle Goodman, Lisa Gay Hamilton, Kristen Johnston, Jane Krakowski, Patti LuPone, Camryn Manheim, Donna Murphy, Kathy Najimy, Lois Smith and Marisa Tomei.

Also listed are film and television talents including Winona Ryder ("Girl, Interrupted"), Rhea Perlman ("Cheers"), Julianna Margulies ("ER"), Lara Flynn Boyle ("The Practice," "Happiness") and talk show host Ricki Lake. Perhaps the three most unusual women to be connected with the play are journalist Linda Ellerbee, novelist Erica Jong ("Fear of Flying") and pop sensation Morissette.

Mary Alice, Amy Irving, Rosie Perez, Audra McDonald, Swoosie Kurtz and Julie Kavner have already appeared in the production.

No scheduling beyond the first five groups has been announced. The set schedule will run as follows:

March 21-April 2: Shirley Knight, Andrea Martin, Alanis Morissette
April 4-16: Gina Gershon, Annie Potts and Lynne Thigpen

Joe Mantello, who staged Love! Valour! Compassion! on Broadway, is the director of the show.

$10 of each ticket sold to The Vagina Monologues will go to the V Day Initiative.

For information on the Westside engagement, call (212) 239-6200.

-- By Robert Simonson