Fig. The PER positive cells in protocerebrum of Blattella germanica . A.Group IV with clear axons. B. 3 cells of group V with axons. C. One cell of group V with large cytoplasm/nucleus rate. D. One cell of group VI (solid arrow) near a cell of group V (broken arrow) with different morphology. E. Group VII and one cell of group IV (arrow) with different immunoactivity and cytoplasm/nucleus ratio. Scale bar: 50 μ m.