Primary oocyte in division

Secondary oocyte and polar body 1

Polar body in division

Figure 1.20 Maturation of the oocyte. A. Primary oocyte showing the spindle of the first meiotic division. B. Secondary oocyte and first polar body. The nuclear membrane is absent. C. Secondary oocyte showing the spindle of the second meiotic division. The first polar body is also dividing.

membrane of the secondary oocyte in the perivitelline space (Fig. 1.20B). The cell then enters meiosis II but arrests in metaphase approximately 3 hours before ovulation. Meiosis II is completed only if the oocyte is fertilized; otherwise, the cell degenerates approximately 24 hours after ovulation. The first polar body also undergoes a second division (Fig. 1.20C).

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