Histological characteristics of gametogenesis of two kinds of scallops, gonochoric Chinese scallop,Chlamys farreri and hermaphroditic bay scallop,Argopecten irradians were investigated in this study. Spermatogenesis inC. farreri has different developmental stages: spermatogonia, primary spermatocyte, second spermatocyte, spermatid and spermatozoon. A large number of same developmental stage spermatic cells converge at a definite area of the testis. Premeiotic, previtellogenic and vitellogenic oocytes can be found during oogenesis inC. farreri, where oocyte distribution is obviously irregular. TheA. irradians gonad consists of two different parts in one individual: one part functions as testis, the other as ovary. Between these two parts is a special appearance area, where a large number of spermatic cells are bound with two layers of acellular substance with many oocytes in it.