Affiliation: | 1. Zoology Dept. , Downing Street , Cambridge, CB2 3EJ, to whom requests for reprints should be addressed.;2. PowerGen plc, Ratcliffe Technology Centre , Ratcliffe-on-Soar, Nottingham, NG11, OEE;3. Zoology Dept. , University of Nottingham, University Park , NottinghamNG7 2RD;4. Unilever Research, Port Sunlight Laboratory , Wirral, MerseysideL63 3JW. |