1. F. Stuart, The Magic Horns. Folk Tales from Africa, 2nd edn. (Addison-Wesley, Reading, 1976)
2. M.L. Nguyen, North china leopard (panthera pardus japonensis) seen through the glass of its cage. From the zoological garden of the Jardin Des Plantes in Paris. online (2006). http://commons.wikimedia.org/wiki/File:Panthera_pardus_japonensis_JdP.jpg
3. C. Weijer, in The Self-Made Tapestry. Pattern Formation in Nature, ed. by P. Ball (Oxford University Press, Oxford, 1999), p. 71. Published with kind permission of the author
4. A.L. Hodgkin, Biol. Rev. Camb. Philos. Soc. 26(4), 339 (1951). Figure 1.1c published with kind permission of Cambridge University Press
5. R. Scorer, Clouds of the World. A Complete Colour Encyclopedia, 1st edn. (Lothian, Melbourne, 1972)