1. Crumb, Robert (1965). “Fred the Teenage Girl Pigeon.” Help!. Vol. 24. Philadelphia, Warren Publishing, n.p.
2. Crumb, Robert (1968a). Zap Comix. Vol. 1. San Francisco, Apex Novelties.
3. Crumb, Robert (1968b). Head Comix. New York, Viking Press.
4. Crumb, Robert (1968c). “Mr. Natural,” Zap Comix. Vol. 2. San Francisco, Apex Novelties, pp. 44-48.
5. Crumb, Robert (1968d). “Life Among the Constipated,” Head Comix. New York, Viking Press, p. 3.