Characterization of sperm migration through the cumulus matrix in vitro according to the acrosomal status. A) The plots represent the cumulative number of sperm entering the COCs (open circles) and the number of sperm remaining in the COCs (closed diamonds) at given times after insemination. The COCs area was drawn as a broken circle as shown in E. B) In the analysis of type of sperm entering the COCs, an apparent logistic increase of acrosome-intact sperm (green), and a relatively low but constant increase of acrosome-reacted sperm (orange), were seen. C) In respect to the sperm number remaining in the COCs, acrosome-intact sperm (green) reached a maximum at ~40 min post-insemination, followed by the rapid accumulation of acrosome-reacted sperm (orange). D) Representative time course of the average residence time of acrosome-intact (green) and acrosome-reacted (orange) sperm in the COCs estimated from equations (Materials & Methods). E) Representative photographs show a transition of the sperm population (from acrosome-intact to acrosome-reacted) as a function of time; scale bar, 100μm.