(A) Wild-type ovary which is occupied with many eggs. The asterisk indicates the ovarian cavity, where ovulation of mature eggs occurs. The ovarian cavity represents the structure of ovaries. (B) Mutant ovary with ovarian cavity (asterisk) without eggs. In this ovary, only sexually indifferent germ cells are present (arrowheads). Due to the feminizing effect of these germ cells, medaka can form ovaries and become female.