Hentschel 2002, pp. 63–64. Hentschel, Linda (2002). "Pornotopic Techniques of the Observer – The Origins of the World (1866) by Gustave Courbet and the Pleasure of Scopic Penetration". In Härtel, Insa; Schade, Sigrid (eds.). Body and Representation. Opladen, Germany: Leske + Budrich. pp. 59–67. ISBN978-3-8100-3254-6.