Ultrastructural observations of fertilization in the Japanese long-fingered bat, Miniopterus schreibersii fuliginosus.

Only a very few spermatozoa were found in the ampulla of the oviduct just after ovulation. The spermatozoa lost both the acrosome cap and the equatorial segment while passing between the cumulus cells surrounding an ampullar egg; many such spermatozoa were found in the perivitelline space. One spermatozoon was seen in contact with the plasma membrane of the ovum in the metaphase of the second meiotic division. Excess spermatozoa in the perivitelline space were phagocytosed by pseudopodial protrusions from the blastomere surface.