Each ovary of the female fruit fly houses multiple ovarioles or ‘assembly lines’ in which individual egg chambers develop into fully formed fly eggs. Each egg chamber consists of 16 large germline cells (one of which is the future egg cell), surrounded by a thin sheet of smaller cells. In this picture, cross-sections of ten ovarioles from different female fruit flies are arranged with stem cells and early stage egg chambers at the center, and the more mature chambers at the periphery. The nucleus of each cell is stained yellow/orange. The cell membranes are stained blue.