High power TEM of the edge of a pronucleus (Pn) of a stage 1b embryo in vitro, 24 hours post-insemination (original magnification x24,800). Shown are pores in the pronuclear membrane (PnM), an intrapronuclear annulate lamella (IAL) and a nucleolus (N). The pronuclear membrane is very similar to the intrapronuclear annulate membrane.
From: Soupart and Strong, 1974.Reproduced with permission of the American Society for Reproductive Medicine
Source: The Virtual Human Embryo.