Heartbeat -- Stage 34 Seen here at lower magnification and with different lighting, the yellow coloration of the embryo due to the presence of chromatophores is evident. Pink blood flows through branched, sinuous vitelline veins. The embryo is about 168 hours old and will hatch in another 100 hours. You can faintly see the urinary bladder (greenish) and the spleen (reddish).