Bhṛgu, the mind-born son of Brahmā, took his birth again from Carṣaṇī, the wife of Varuṇa, and the great sage Vālmīki appeared from Varuṇa's semen. Agastya and Vasiṣṭha were two sons of Varuṇa and Mitra. Upon seeing the beauty of Urvaśī, Mitra and Varuṇa discharged semen, which they kept in an earthen pot. From that pot, Agastya and Vasiṣṭha appeared. Mitra had a wife named Revatī, who gave birth to three sons-Utsarga, Ariṣṭa and Pippala.
Agastya and Vasistha were two sons of Varuna and Mitra
SB Canto 6
Upon seeing Urvaśī, the celestial society girl, both Mitra and Varuṇa discharged semen, which they preserved in an earthen pot. The two sons Agastya and Vasiṣṭha later appeared from that pot, and they are therefore the common sons of Mitra and Varuṇa. Mitra begot three sons in the womb of his wife, whose name was Revatī. Their names were Utsarga, Ariṣṭa and Pippala.
Modern science is trying to generate living entities in test tubes by processing semen, but even long, long ago it was possible for semen kept in a pot to develop into a child.