The Time Sequence of Ovum Maturation in the Rat

Summary. Follicular oocytes were examined at various times preceding ovulation. The timing of the preovulatory changes was established in relation to the `critical period' and to ovulation time. The earliest detectable change in the oocyte, loss of the germinal vesicle and the nucleolus, occurred about 2 hr after the presumed time of lh release, or about 9 hr before ovulation. The first polar body was extruded about 4 hr before ovulation. The morphology of the dictyate oocyte as revealed by interference contrast microscopy is described.