Prolonged survival of the Graafian follicle and fertilization in the Japanese greater horseshoe bat, Rhinolophus ferrumequinum nippon.

After the mating season of the Japanese greater horseshoe bat in mid- or late October, only the right ovary maintained a single Graafian follicle throughout hibernation until early April. During this time the ovum was in prophase of meiosis I (resting stage) with many large lipid droplets as a nutrient source. In synchrony with stigma formation, there was resumption of meiotic activity, separation of the cumulus oophorus from the granulosa layer and dispersion of the follicle cells just before ovulation in spring. The block to polyspermy seemed to reside in the zona pellucida, because no spermatozoa could be detected in the perivitelline space of the 6 fertilized ova examined, although a second spermatozoon was recognized in the zona pellucida of 3 ova.