Localization of fluorescent beads in the placental labyrinth following exocoelomic microinjection. Images of placentas dissected at E11.5 following ultrasound-guided microinjection of green fluorescent beads into the exocoelomic cavity at E7.5. (A) Stereomicroscopic image showing fluorescent beads embedded in the fetal surface of the placenta near the cord insertion. (B) 50 μm frozen section through the placenta and implantation site showing fluorescent beads distributed within the labyrinth layer, extending as deep as the border between the labyrinth and spongiotrophoblast layers (dotted line). Boxed regions in (B) and (C) are shown as higher power images in (C) and (D) respectively. Cell nuclei were stained with DAPI in B, C, and D. AC, amniotic cavity; Emb, embryo.