
Figure 1. Photographs of a bisected sturgeon egg (oocyte), before (at the left side) and after (at the right side) incubation in progesterone solution. Before incubation, notice the position of the nucleus (GV) embedded in the cortical cytoplasm of the animal pole region. After incubation in progesterone solution (picture at the right), if the oocyte is matured, it will undergo germinal vesicle breakdown or GVBD; the nuclear membrane disintegrates and the GV is no longer visible.