The ventral side is decorated with ocelli (eyespots). The hindwings are tailed and have ridged edges containing reddish eyespots. The blunt, triangular head has two ocelli (eyespots), pigmented areas that are sensitive to light. The hindwings may also have eyespots or white dots. There are eyespots on the outer forewings. Many butterflies and moths have eyespots, wing markings that resemble eyes. In later instars, the eyespots on the thorax serve to deter birds. The swollen thorax has two black, yellow, and blue eyespots. Saturniids are sometimes brightly colored and often have translucent eyespots or "windows" on their wings. At the head of the planarian there is a ganglion under the eyespots. The eyespots are thought to confuse potential predators. These eyespots are brilliantly coloured concentric circles. Amongst jawless fish, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. Males with fewer eyespots, thus with lower mating success, suffered from greater predation. The cells have anterior eyespots that enable the colony to swim towards light.