1. Department of Biological Sciences, University of Paisley, Paisley PA1 2BE, Scotland, United Kingdom (W.F.); and
2. Arbeitskreis Kinematische Zellforschung, Biozentrum der J.W. Goethe-Universität, Marie-Curie-Strasse 9, D–60439 Frankfurt, Germany (W.S.P.)