1. Biological Laboratory, The Open University of Japan, Wakaba, Mihama-ku, Chiba 261-8506, Japan
2. Department of Tropical Medicine and Parasitology, School of Medicine, Juntendo University, Hongo, Bunkyo-ku, Tokyo 113-8421, Japan
3. Department of Computer Science, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan
4. Department of Biological Science, Graduate School of Arts and Sciences, the University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan