Fine structure of undifferentiated gonads inRana dalmatinatadpoles

The ultrastructure of Rana dalmatina tadpoles’ gonads is described during two early stages of development: the primary and the secondary undifferentiated condition. The gonadal bud structure in the first stage of differentiation is characterized, and it is clearly demonstrated that the cortex and the medulla are lined by an uninterrupted basal lamina along the margin adjacent to the primary cavity. The basal lamina that lines the cortex is a continuation of the one delimiting the somatopleura. In the second stage, it is shown that the medulla delaminates to form a secondary gonadal cavity known as the ovarian pocket, and that the cortex contains early germ cells, both isolated and undergoing mitotic division, corresponding to a germinal epithelium. In addition the diplotenic oocytes form a distinct layer within the primary gonadal cavity between the cortex and medulla. Each of the three layers (germinal epithelium, diplotenic oocytes, and hollow medulla) is delimited by its own basal lamina. The ultrastructure of the different germ and somatic cells is described.