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Fig. 1
Gonadal development and differentiation. Indifferent gonad (a), only primordial germ cells (PGCs) are found in the gonad at 5 d.p.f. PGCs contain a large nucleus and possess a distinct nuclear membrane, several big nucleoli, and a network of fine chromatin filaments distributed throughout the karyoplasm. Along the inner side of the nuclear membrane, deeply staining granulosa material is seen. The weakly stained cytoplasm accounts for only a small fraction of the cell volume. At 7 d.p.f., PGCs differentiate into gonocytes (Gc). At 11 d.p.f., more Gcs and meiotic gonocytes with condensed chromatin (Cn) are seen, in addition to PGCs. At 17 d.p.f., early perinucleolar oocytes (EPOs) appear. During juvenile gonadal differentiation toward the ovary (b), more meiotic germ cells are seen (23 d.p.f.), showing densely packed oocytes (27 d.p.f.) and tight connections between late perinucleolar oocytes (LPOs) at 35 d.p.f. In the presumptive testis (c), stromal cells increase and oocyte degenerations appear as acid staining cells (Ac). Sc, spermatogonia cyst. Scale bar=20μm