High power TEM of a section of a blastomere of a stage 2, 4-cell embryo in vivo (original magnification x30,000). Small, flattened saccules (arrows) are closely related to dense mitochondria.
N = nucleus
From: Pereda and Croxatto, 1992. Reproduced with permission of the Annals, Academy of Medicine, Singapore.
Keywords: four-cell embryo, mitochondria, nucleus, saccule(s)
Source: The Virtual Human Embryo.