The sheath appears to tonically contract as it pulls the dilating distal spermatheca over the most proximal oocyte. As the distal spermatheca closes, cytoplasmic streaming is visible in the oocyte, possibly indicating fertilization. Entry into the uterus occurs 4.2 minutes after ovulation. The meiosis I and II divisions occur in the uterus. In unmated females, oocytes arrest in diakinesis, failing to undergo meiotic maturation and ovulation for hours or days.
Numerous oocytes accumulate, each with an enlarged, distally positioned nucleus lacking a nucleolus.
This phenotype defines the arrest point, and separates the events belonging to oocyte development from those of meiotic maturation. Additionally, sheath contractile activity in females is lower than the background level observed between ovulations in hermaphrodites. In hermaphrodites, oocyte development, maturation, and ovulation occur in an assembly-line fashion with an ovulation rate of about once per 45 minutes while sperm are present. The time an oocyte spends in diakinesis may reflect a developmental requirement for the execution of certain events and thus might not be a true 'arrest' of the cell cycle. While the events of oocyte development, maturation, and ovulation occur in a reproducible order, the dependency relationships for these events are not yet defined.