Abstract
Summary. The sequence of morphological changes in the nuclei of follicular oocytes in the pig has been examined after a single injection of human chorionic gonadotrophin (hcg), given during pro-oestrus. Oocytes remained in the germinal vesicle (dictyate) stage until 18 hr after injection of hcg. Chromatin condensation, followed by completion of prophase of the first maturation division, then occurred, and the chromosomes were arranged on the first metaphase spindle by 26 hr after hcg. From 26 until 34 hr after hcg, the chromosomes remained at first metaphase, but between 35 and 37 hr, anaphase, telophase and abstriction of the first polar body were completed. The great majority of eggs recovered from individual animals showed similar stages of maturation.