Human fetus at 16 weeks gestation, measuring approximately 110 mm (crown to rump). At this stage, the fetal face and limbs are well formed, fingernails can be seen on the hands, and fingerprints have developed on the skin. The eyes are sealed shut but are sensitive to light, and the fetus can hear and respond to some sounds with movement. The fetal bones have been stained with a dye which only stains the calcified regions.