J. Spiller, Paul Klee: Das bildnerische Denken. Formund Festaltungslehre, Basel, 1956, p. 396 (illustrated).
G. di San Lazarro, Klee: A Study of His Life and Work, London, 1957, p. 299, no. 124 (illustrated, p. 276).
R. Verdi, "Musical Influences on the Art of Paul Klee," Art Institute of Chicago Museum Studies, 1968, vol. 3, pp. 93 and 106, footnote 23.
W. Grohmann, Paul Klee, London, 1969, p. 336, no. 166 (illustrated, p. 404).
M. Huggler, Paul Klee: Die Malerei als Blick in den Kosmos, Stuttgart, 1969, pp. 170-172.
E. Bauer, Paul Klee: Innere Wege, exh. cat., Wilhelm-Hack-Museum, Ludwigshafenam Rhein, 1981, pp. 28 and 32, footnote 15.
M.F. Popia, L'estetica di Paul Klee, Ph.D. Diss., Università degli studi di Genova, 1999, p. 33 (illustrated).
The Paul Klee Foundation, ed., Paul Klee: Catalogue Raisonné, 1934-1938, Bonn, 2003, vol. 7, p. 302, no. 7125 (illustrated).