1. Department of Biological Sciences, Institute of Environmental and Natural Sciences, Lancaster University, Bailrigg, Lancaster LA1 4YQ, U.K.
2. The Polymer Centre, School of Physics and Chemistry, Lancaster University, Bailrigg, Lancaster LA1 4YA, U.K.
3. Shriners Hospital for Crippled Children, 12502 N. Pine Dr., Tampa, FL 33612-9499, U.S.A.