internal genital organs in concordance with the development of external characteristics in male . The results showed that external sexual characteristics appeared with the development of internal genital organs. Only testicular cords with many spermatogonium in itcould be observed at 8~14 days after hatching.exual characteristicsduring the same period. External young lucid paired lobed penis, appendix masculine at the antennule peduncle and the fourth abdominal appendage occurred at14~20 days after hatching. Spermatocytic sacculations in testis could be observed at 14~20 days after hatching. At 24~30 days after hatching, male reproduction system matured. The results of the study will help for study on the biology and artificial culture of mysis.