1. Haeckel, E. H. P. Art Forms in Nature revised edn (Dover Publications, New York, USA, 1974).
2. Mattheck, C. Design in Nature: Learning from Trees (Springer, Berlin, 1998).
3. Xu, Y. D. & Zhang, L. T. Composites 26, 315–318 (1995).
4. Hoedeman, J. J. Naturalists' Guide to Fresh-water Aquarium Fish (Sterling/Oak Tree, New York, 1974).
5. Colbert, E. H. Evolution of the Vertebrates: A History of Backboned Animals Through Time Vol. 16 (Wiley, New York, 1955).