PROFESSORS P.M. MOTTA & S. MAKABE / SCIENCE PHOTO LIBRARY PROFESSORS P.M. MOTTA & S. MAKABE / SCIENCE PHOTO LIBRARY
False-colour scanning electron micrograph of two primordial egg cells (blue), also known as primary oocytes, on the surface of the ovary of a developing embryo. The progenitors of these cells migrate from the yolk sac towards the developing gonads, the future ovaries, arriving at the end of the fourth week after fertilisation. At this stage they are known as oogonia. Some of them differentiate into primary oocytes and begin their first meiotic division. At birth a primary oocyte, known as a primordial follicle, consists of the ovum surrounded by a layer of flat epithelial cells. Magnification: x2840 at 6x7cm size.
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