On July 11, just days before Lincoln Center Theater's The Frogs was to go before the critics, Lincoln Center Theater announced that Tony Award winner Roger Bart would replace "Saturday Night Live" actor Chris Kattan in the revised revival of the Stephen Sondheim musical.

The move came after three weeks of previews.

Bart plays the role of Xanthias, the sidekick to Dionysos, played Nathan Lane, who rewrote the Burt Shevelove libretto, which was inspired by Aristophanes.

The new casting marks a reunion of Producers veterans Bart, Lane and director-choreographer Susan Stroman.

A release from the show's press representative simply stated that Kattan had withdrawn from the production, and did not cite a reason for the departure. While Bart was rehearsing, understudy Timothy Gulan performed the part of Xanthias starting July 12. The show will open July 22 as planned. Performances continue to Oct. 10.

Bart was Tony-nominated for the role of Carmen Ghia in the Mel Brooks musical, after having previously won the award for You're a Good Man, Charlie Brown.

The Frogs, "freely adapted" from the Aristophanes comedy by Burt Shevelove, "even more freely adapted" by Nathan Lane, features music and lyrics — including a half dozen new tunes — by Stephen Sondheim.

This marks star Lane's first attempt at writing a musical theatre libretto.

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About the production, Sondheim told the New York Times, "It's not a revival. The old one was only about 40 minutes long. Nathan has really expanded it."

The songlist has also expanded. As of the first preview, the score ran as follows:

"Invocation and Instructions to the Audience"
"I Love to Travel"
"Dress Big"
"I Love to Travel"
"All Aboard"
"Adriadne"
"The Frogs"
"Hymn to Dionysos"
"Hades"
"It's Only a Play"
"Shaw"
"All Aboard"
"Fear No More" (lyrics from Shakespeare's Cymbeline)
"Hymn to Dionysos"

The songlist of a 2001 recording of the 1974 score ran as follows:

"Fanfare"
"Prologue: Invocation and Instructions to the Audience"
"Traveling Music"
"Parados: The Frogs"
"Hymnos: Evoe!"
"Dialogue: 'Pluto!'"
"Parabasis: It's Only a Play"
"Dialogue: 'That Was Some Banquet!'"
"Evoe for the Dead"
"Invocation to the Muses"
"Fear No More"
"Exodos: The Sound of Poets"

Nathan Lane stars as Dionysos in the musical, which is based on the Aristophanes classic. The ancient play focuses on a debate between Aeschylus and Euripides, to determine who is the greater artist. The winner of the contest returned to Earth with Dionysos to save civilization.

Sondheim (Assassins) and librettist Burt Shevelove wrote the show for a production staged in the Yale swimming pool in 1974. The story was updated to feature a debate between William Shakespeare and George Bernard Shaw and has traditionally required elaborate special effects, a large cast of actors skilled in both acting and swimming and an exhibition pool in which they perform. (No massive pool has been added into the Vivian Beaumont at Lincoln Center Theater.)

That 1974 cast included Larry Blyden as Dionysos, Michael Vale as his slave, Charles Levin as Charon, Jerome Dempsey as Pluto, Jeremy Geidt as Shakespeare and Anthony Holland as Shaw. There was also a large chorus of Yale students which included Christopher Durang, Meryl Streep and Sigourney Weaver, among others.

Two of the more known songs to emerge from the show are "Fear No More," a setting of Shakespeare verse by Sondheim, and "Invocation to the Gods and Instructions to the Audience," which was once the opening number of the score of A Funny Thing Happened on the Way to the Forum (replaced by "Comedy Tonight"), and was later heard in a revised form in the revue, Putting It Together.

Also in the cast are John Byner (Charon), Peter Bartlett (Pluto), Daniel Davis (Shaw), Burke Moses (Herakles) and Michael Siberry (Shakespeare).