Srimad Bhagvata Mahapurana: Book 8: Chapter 14: Verses 1-11
Functions of a Manu and other functionaries holding office in his administration
he king (Pariksit) submitted : (Pray,) tell me this, O worshipful one, as to how and which of these, Manu and others, are employed in what work and by whom in the (various) Manvantaras. The sage Suka replied : The Manus and the sons of a Mau, the sages and the Indras, as well as the (diverse) orders of gods, O ruler of the earth, are all under the (direct) command of the supreme Person (in the form of His part manifestations in each Manavantara). Whatever forms (part manifestations) of the supreme Person, Lord yajna and so on, have been mentioned (by me before), O protector of men -directed by these, the Manu and others carry on the administration of the universe. At the end of (each round of) the four yugas, the seers by virtued of their asceticism discover as they are ( and teach the) the collections of the Vedic texts, swallowed by Time, with (the help of) which (the truth of) the eternal religion is perceived. Instructed by Sri Hari (dwelling in their heart) and (fully) alert (in their mind), the manus then directly propagate on the earth in their own time piety with (all) its four limbs (asceticism, purity of mind and body, compassion and truth), O protector of human beings! The protectors of created beings (viz., the sons of a Manu along with their descendants from generation to generation) protect religion (as well as the earth) till the end (of a Manvantara) by parts (each generation carrying on the work of protection for a part of the Manvantara alone). And the gods along with those (others, viz., the Rsis, the Pitrs, human beings and other living beings) that are connected with the Performance of (the five great) sacrifices enjoy a share in the sacrificial offerings (and thus they too protect religion).
Enjoying the limitless wealth of (all) the three worlds (heaven, earth and the intermediate region), conferred (on him) by the Lord, Indra protects those three worlds and sends down profuse showers in the world according to his will. Nay, assuming the form of Siddhas (perfect beings like the sage Sanaka and his three brothers-Sanandana, Sanatana and Sanatkumara) Sri Hari imparts wisdom in every Yuga; taking the form of Rsis (seers like the sage Yajnavalkya) He preaches (the cult of) rituals and, appearing in the form of Masters of Yoga (like Dattatreya) it is He who teaches (the methods of) Yoga (to the world). (Appearing) in the form of lords of created beings (like the sage Marici), He carries on creation; taking the form of an independent ruler, He destroys robbers; (and) assuming diverse characteristics (such as heat and cold) in the form of Time, it is He who makes for the disappearance of all. Though depicted (diversely) by these (so-called learned) people- whose understanding is (as a matter of fact) deluded by Maya, consisting of (so many) names and forms- through different systems of philosophy, the Lord is (actually) not perceived (by them). The aforesaid has been precisely declared to be the duration of a minor Kalpa (covering a day of Brahma and) forming part of a Mahakalpa (covering the whole lifetime of Brahma). In this Kalpa, those well-versed in the ancient lore say, are comprised fourteen Manvantaras.
Thus ends the fourteenth discourse in Book Eight of the great and glorious Bhagavata-Purana, otherwise known as the Paramahamsa-Samhita.