Fig. 2.

Ultrastructure of human mature oocyte with bull-eye inclusion. a Semithin section. Note the zona pellucida (ZP), the metaphase II plate (white arrowhead), and the first polar body that is divided (1PBd). The bull-eye inclusion (arrow) is surrounded by several light round structures (black arrowhead). b–f Ultrathin sections. b, c The oocyte cortex contains cortical vesicles (cv), isolated smooth endoplasmic reticulum (SER) vesicles (v) and tubules (t), and moderate dense mitochondria (m). Note the ZP, the perivitelline space (PVS), microvilli (mv), the 1PBd, and the metaphase II plate (white arrowhead). d The bull-eye inclusion (BE) presents prominent contents and is surrounded by lipid droplets (black arrowheads). e The surface of the inclusion is devoid of a limiting membrane (arrows) and is surrounded by moderate dense lipid droplets (L). The interior of the inclusion is made of medium and small vesicles (V). Medium vesicles present an internal dense amorphous structure at one of the poles (white arrowhead). f The vesicles of the inclusion appear delimited by a double membrane (black arrowheads). a 20 μm. b–d 1 μm. e 0.5 μm. f 0.25 μm