1. Laboratory of Veterinary Pathology, Faculty of Agriculture, Kagoshima University, Kagoshima 890, Japan
2. Laboratory of Veterinary Medicine, Faculty of Agriculture, Kagoshima University, Kagoshima 890, Japan
3. Laboratory of Ecology, Department of Biology, Faculty of Science, University of the Ryukyus, Okinawa 903-01, Japan
4. Laboratory of Ecology, Department of Biology, Faculty of Science, Kyusyu University, Fukuoka 812, Japan