The function of the parietal eye is unknown, but it may be useful in absorbing ultraviolet rays to manufacture vitamin D. It may also do other things. Of all living tetrapods, the parietal eye is most obvious in this animal. The parietal eye is part of the pineal system. The animal's pineal gland secretes melatonin at night. Some salamanders use their pineal body to perceive polarised light, which helps navigation. Unlike lizards they have no eardrums or external male sexual organ.