Leopold Zahn, Paul Klee. Leben, Werk, Geist, Potsdam, 1920, illustrated p. 85 Hans Hildebrandt, Die Kunst des 19. und 20. Jahrhunderts, Wildpark-Potsdam, 1931, p. 422 Will Grohmann, Paul Klee, Geneva & Stuttgart, 1954, p. 144 Gualtieri di San Lazzaro, Klee, La vie et l'oeuvre, Paris, 1957, illustrated James Smith Pierce, Paul Klee and the Primitive Art, New York & London, 1976, pp. 43 & 46 K. Porter Aichele, 'Paul Klee's Operatic Themes and Variations' in The Art Bulletin, vol. 68, no. 3, September 1986, illustrated p. 460 Sarah Lynn Henry, 'Paul Klee's Pictorial Mechanics from Physics to the Picture Plane' in Pantheon, vol. 47, 1989, p. 156 Jenny Anger, Modernism and the Gendering of Paul Klee, Dissertation, Brown University, 1997, pp. 205 & 207 Paul Klee Stiftung (ed.), Paul Klee, Catalogue raisonné, Bern, 1999, vol. III, no. 2379, illustrated p. 164 (catalogued incorrectly as oil and watercolor on paper) Meira Perry-Lehman, ed., Modern Masterworks on Paper from the Israel Museum (exhibition catalogue), Jerusalem, 1999 Robert Kudielka, Paul Klee – The Nature of Creation, Works 1914-1940 (exhibition catalogue), Hayward Gallery, London, 2002