Stage V

Stage V oocytes range in size from 1000 to 1200 |im and account for 10% of the oocyte population in stages II to VI. At this point in oogenesis, the border between the animal and vegetal hemispheres becomes more distinct, and the pigmentation of the animal hemisphere begins to fade from the dark brown of stage IV oocytes to a more brown or beige color. Blood vessels are still prominent, the vitelline envelope has reached maximal thickness, and follicle cells appear to flatten. At this point, vitel-logenesis starts declining, although the yolk gradient continues to displace the nucleus toward the animal pole. At this point, the nuclear envelope polarizes such that the vegetal half of the nucleus becomes more irregular than the animal half, and the nucleoli and chromosomes condense to form a centrally located mass.

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