Fig. 15. High power TEM of a stage 4 embryo in vitro showing details of the contact zone between the endometrial cells (EC) and a cytotrophoblast cell (CTr). Measuring bar = 0.5 µm . The plasmalemma of the endometrial cells exhibit many invaginations (arrows) where it is adjacent to the cytotrophoblast cell protrusions. The endometrial cells have a Golgi complex (G), mitochondria (M), well-developed rough endoplasmic reticulum (RER), and an electron dense matrix. (From: Lindenberg et al., 1986. Reproduced with permission of the publisher, Oxford University Press.)