Human CO, SFO and VO at MII stage. M-SER aggregates and MV complexes. By TEM, voluminous M-SER aggregates are seen in (a) (CO) and (b) (SFO cultured for 3–4 hours). Small MV complexes are also observable in (b). M-SER appear partially replaced by numerous and larger MV complexes after prolonged culture, as seen in (c,d) (VO cultured for 8–9 hours). Mitochondria (M) are well preserved in both SFO (b) and VO (d). Bar is: 1 μm (a,b,d); 2 μm (c).