The pineal eye, or parietal eye, in the tuatara, some lizards, and many frogs, serves as a light sensor that then influences the brain. Glands in the brain of these animals (like the pineal gland) are "informed" by the sensor regarding ambient light, time of day, and day length and can then act to regulate circadian rhythms, adjust thermoregulation, and even regulate the onset of sexual and mating activity