Pineal Gland
The pineal gland is an endocrine gland which is located somewhat centrally in the brain, between the two lobes of the brain. It is where the circadian rhythms is translated into chemical messenger. The pineal gland secretes melatonin.
References
Gray, H. 1977. Gray's Anatomy. Crown Publishers, Inc. New York. 1257 pp.
Hadley, M.E. 1984. Endocrinology Prentice-Hall, Inc. New Jersey. 547 pp.
Reiter, Russel J. 1991. Melotonin: the chemical expression of darkness. Molecular and cellular Endocrinology. 79: 153-158.