Off-target beads following 69 nL microinjection into the amniotic cavity. This E7.5 conceptus was dissected a few hours after ultrasound-guided microinjection of a 69 nL volume containing 3 μm diameter fluorescent beads into the amniotic cavity. (A) The amniotic and yolk sac cavities were visibly distended (e.g. compare to figure 3D) when viewed under a dissection microscope. (B) When the same embryo was viewed under a fluorescent microscope, beads were visible within the amniotic cavity (arrow) but were also present in the adjacent exocoelomic cavity as well as in the ectoplacental cone region. AC, amniotic cavity; EPC, ectoplacental cone region; Exo, exocoelomic cavity; YSC, yolk sac cavity.