Pre-implantation development of the ICSI embryos. (A) Samples were collected after two sperm heads were injected into the 2-cell–like MII oocytes for 24 hours. Time points when most embryos reached the 2-cell stage are shown. Arrowheads indicate the second polar bodies. Green, microfilaments; red, microtubules; blue, DNA. Bar = 20 μm. (B) ICSI blastocyst that forms a MII oocyte with a large polar body (arrows).