according to their ultrastructure , the following main cell classes were distinguished : gonocytes ( 37 to 43-day foetuses ) , prespermatogonia ( 50 to 110-day foetuses ) , pale type a ( ap ) and dark type a ( ad ) adult-type spermatogonia which differentiated progressively in 120 to 140-day foetuses .
C0007634
cell
C0007589
differentiated