Fig. 9 . Low power TEM of a stage 4 embryo in vitro. Measuring bar = 10 µm. Blastocyst is attached to the endometrial cell culture. Bl, expanded blastocystic cavity; EC, endometrial cell; Ep, epiblast; Hy, hypoblast; MTr, mural trophoblast; PTr, polar trophoblast. Arrows show level of endometrial cells. (From: Lindenberg et al., 1986. Reproduced with permission of the publisher, Oxford University Press.)