1. Laboratory of Anatomy, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Hokkaido, Japan
2. Section of Biological Safety Research, Chitose Laboratory, Japan Food Research Laboratories, Chitose, Hokkaido, Japan
3. Department of Histology and Cytology, Faculty of Veterinary Medicine, Zagazig University, Zagazig, Egypt