Depiction of the six stages (st.; I–VI, from left to right) of oogenesis in Xenopus. The diameters of each oocyte, stages of vitellogenesis (or yolk accumulation, and the animal-vegetal (AV) axis are shown. The nuclei (or germinal vesicles [GVs]) are indicated by circles, and the Balbiani Body in the stage I oocyte is depicted in gray on the vegetal side of the GV, which is in the center. In the stage IV oocyte, the GV is displaced toward the animal hemisphere, where accumulating pigment is indicated by brown shading. The GV is further displaced toward the animal hemisphere in stage V and VI oocytes, where accumulated pigment is indicated by dark brown shading and increased yolk accumulation is indicated by yellow shading.