PHILADELPHIA - Famous for making artwork out of a mass-produced urinal, artist Marcel Duchamp also created the lesser-known, more mysterious "Étant Donnés," now the object of a fascinating, scholarly show. Organized by Michael Taylor at the Philadelphia Museum of Art, the exhibition documents the assemblage that secretly occupied Duchamp for his last 20 years. The hallucinations within "Étant Donnés" can be viewed only through two peepholes drilled into a weathered wooden door.