1. Department of Biology, Graduate School of Science; Kobe University; Kobe 657-8501 Japan
2. Evolutionary Morphology Laboratory; RIKEN; Kobe 650-0047 Japan
3. Laboratory of Veterinary Anatomy; the University of Tokyo; Tokyo 113-8657 Japan
4. Development and Function of Inhibitory Neural Circuits, Max Planck Florida Institute for Neuroscience, Jupiter, Florida 33458; USA
5. Division of Biology; Hyogo College of Medicine; Nishinomiya Hyogo 663-8501 Japan
6. Laboratory of Physiology; Atmosphere and Ocean Research Institute, the University of Tokyo; Chiba 277-8564 Japan