The resultant serotonin is further metabolised into melatonin by the pineal gland. Tumors of the pineal gland are called pinealomas. The primary function of the pineal gland is to produce melatonin. The pineal gland is a midline brain structure that is unpaired. The Ajna chakra is correspondent with the pineal gland. Melatonin is a hormone secreted by the pineal gland in darkness, normally at night. The secretory activity of the pineal gland is only partially understood. The morphology of the pineal gland varies greatly among mammals. The morphology of the pineal gland differs markedly in different pathological conditions. Macrodontia of all the teeth is known to occur in pituitary gigantism and pineal hyperplasia. Nearly all vertebrate species possess a pineal gland. The level of vascularization in the pineal gland is high. In response, the pineal secretes the hormone melatonin. Nearly all adults show calcification of the pineal gland. This may contribute to lowered levels of monoamines in aged brain and pineal gland.