Ultrastructure of spermatogenesis and spermiogenesis in the grey mullet (Mugil cephalus)

The ultrastructure of sper matog enesis and spermiog enesis in the grey mullet(Mugil cephalus) is investigated by means of transmission electron microscope.The results reveal that there are two types of spermatogonia, Type A and Type B,in the early developmental stage of testes.Nuages appear around nucleus in Type B spermatogonia,which indicates that sper matogonia are ready to develop into primary spermatocytes.Pairing of autochromo-somes is clearly observed in the early period of meiosis in the primary spermatocytes.There exist cell junctions between the two spermatids.Matured sper matozoo n is composed of head,midpiece and tail.The head has a horse-hoo-flike nucleus with a shallow nuclear hollow.There is not any acrosome in front of nucleus.Chromtin within nucleus is rough granule in shape and there is a larger space between nuclear membrane and cytoplasmic membrane. The midpiece of spermatozoon is short.The proximal centriole and distal centriole are perpendicular to each other. The tail is long and there is a pair of lateral fins along the two sides of flag ellum.The flagellum shows a typical microtube organization of "9+2" in the view of cross-section.The ultrastructural character istics and endocrine functions of the non-germinal cells,both Sertoli cell and Leydig cell,in the mullet testes are also discussed.