Maha-Visnu in the Causal Ocean
"The first descent of the Supreme Personality of Godhead ...is the purusa incarnation, Maha-Visnu. It is confirmed in Srimad-Bhagavatam (1.3.1) that when the Supreme Personality of Godhead descends as the first purusa incarnation of the material creation, He immediately manifests sixteen elementary energies. Known as the Maha-Visnu, He lies within the Causal Ocean, and it is He who is the original incarnation in the material world. He is the Lord of time, nature, cause and effect, mind, ego, the five elements, the three modes of nature, the senses and the universal form. Although He is master of all objects movable and immovable in the material world, He is totally independent.
...Innumerable universes are produced from the pores of the Maha-Visnu's body. As innumerable particles of dust pass through the tiny holes in a screen, similarly from the pores of the Maha-Visnu's body innumerable universes emanate. As He breathes out, innumerable universes are produced, and as He inhales, they are annihilated. All of the energies of the Maha-Visnu are spiritual, and they have nothing to do with the material energy...
The second Visnu incarnation, the Garbhodakasayi Visnu, enters each and every universe, spreads water from His body, and lies down on that water. From His navel, the stem of a lotus flower grows, and on that lotus flower the first creature, Brahma, is born. Within the stem of that lotus flower are fourteen divisions of planetary systems, which are created by Brahma. Within each universe the Lord is present as the Garbhodakasayi Visnu, and He maintains each universe and tends to its needs. Although He is within each material universe, the influence of material energy cannot touch Him. When it is required, this very same Visnu takes the form of Lord Siva and annihilates the cosmic creation. The three secondary incarnations--Brahma, Visnu and Siva--are the predominating deities of the three modes of material nature. The master of the universe, however, is the Garbhodakasayi Visnu, who is worshiped as the Hiranyagarbha Supersoul. The Vedic hymns describe Him as having thousands of heads. Although He is within the material nature, He is not touched by it.
The third incarnation of Visnu, Ksirodakasayi Visnu, is also an incarnation of the mode of goodness. He is also the Supersoul of all living entities, and He resides on the ocean of milk within the universe."
Teachings of Lord Caitanya, Chapter 8
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.