Briefly, the oocytes in holothurians are initially present as epithelial cells in the germinal epithelium and then bulge into the hemal sinus as they enlarge.
Their unusual location within the cells of the visceral peritoneum of the ovarian tubules suggests that these oocytes are abnormally transported here following their origin in the germinal epithelium on the other side of the hemal sinus (Inoue and Shirai, 1991; Frick et al., 1996).