-classification type A dark type A(Ad): ovoid, deep-stained N,stem cell - Pale type A(Ap): ovoid, pale-stained n differentiate into type B type B: round N, chromatin granules are distributed under nucleus membrane division and differentiate into primary spermatocyte---classification: type A: -dark type A(Ad): ovoid, deep-stained N, stem cell -Pale type A(Ap): ovoid, pale-stained N, differentiate into type B type B: round N, chromatin granules are distributed under nucleus membrane, division and differentiate into primary spermatocyte