1. Zoologisches Institut, Universität München, München 2, Federal Republic of Germany.
2. Biomolecular Study Centre (BIOS), University of Groningen, Nijenborgh 16, 9747 AG Groningen, The Netherlands
3. Department of Zoology, University of Texas, Austin 78712.
4. Biological Institute, Faculty of Science, Tohoku University, Sendai, Japan 980.