1. Section of Biological Science, Chitose Laboratory, Japan Food Research Laboratories, Chitose, Hokkaido 066-0052, Japan
2. Laboratory of Anatomy, Basic Veterinary Sciences, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Hokkaido 060-0818, Japan
3. Department of Histology and Cytology, Faculty of Veterinary Medicine, Zagazig University, Zagazig 44519, Egypt
4. Section of Biological Safety Research, Tama Laboratory, Japan Food Research Laboratories, Tama, Tokyo 206-0025, Japan