The human fetal ovary (24 weeks). Papanicolaou (PAP) staining and immunohistochemistry as indicated in panels. A) Secondary germ cells descend (white arrowheads) from the OSC between mesenchymal cell cords (mcc), enlarge within the cortex (black arrowhead) above the nuclear cluster (nc) or syncytium of germ cells. The arrow indicates a mesenchymal type cell. Expression of MHC class I (B), Thy-1 (C), DR of activated MDC (D), and cytokeratin (CK) accompany primordial and primary follicles (asterisks) and vessels (v). F) H&E staining of rete ovarii showing rete channels (rc). The rete shows no CK expression (G) but show high Thy-1 staining (H). The presence of CD14+ primitive MDC (I), DR+ MDC (J) and CD3 (K) and CD8 T cells (L). M) Numerous oocytes exhibit degenerative changes (vacuolization). A scale bar in (L) for panels A-L. See text for details. Adapted in part from  with permission, © Humana Press.