1. Department of Biology, Imperial College of Science Technology and Medicine (R.J.L.), London, United Kingdom SW7 2AZ
2. School of Biological Sciences, University of Manchester (J.A.S., A.S.I.L.), Manchester, United Kingdom M13 9PT
3. the Department of Biology, National Science Foundation Center for Biological Timing, University of Virginia (J.M.D., M.M.), Charlottesville, Virginia 22903