1. Key Laboratory of The Ministry of Education for Experimental Teratology; Department of Histology and Embryology; School of Medicine; Shandong University; Jinan Shandong P. R. China
2. Department of Human Anatomy; School of Medicine; Shandong University; Jinan Shandong P. R. China
3. Center for Reproductive Medicine; Shandong University; Jinan Shandong P. R. China