Human CO, SFO and VO at MII stage. Main characteristics. By LM (a-c) and TEM (d-f) no overt difference in shape, dimensions and organelle distribution is seen among CO (a,d), SFO (b,e) and VO (c,f). Note the intact ZP (a-c) and the presence of microvilli (mv) on the oolemma (d-f). Numerous vacuoles (Va) are seen in SFO (b,e). O: oocyte; PB: 1st PB; arrow: MII spindle with chromosomes. Bar is: 45 μm (a-c); 5 μm (d-f).