Fig. 1 . Low power SEM of a stage 4 embryo in vitro. Measuring bar = 550 µm. Blastocyst (curved arrow) attached to a buldging area of the endometrial cell culture. Bulging areas of the endometrial surface (straight arrows) exhibit pinopodes (protruding naked surface with many foldings). (From: Bentin-Ley et al. 1999. Reproduced with permission of the publisher, Oxford University Press.)