sa eva purusas tasmad
andam nirbhidya nirgatah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The Lord [Maha-Visnu], although lying in the Causal Ocean, came out of it, and dividing Himself as Hiranyagarbha, He entered into each universe and assumed the virat-rupa, with thousands of legs, arms, mouths, heads, etc.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The expansions of the planetary systems within each and every universe are situated in the different parts of the virat-rupa (universal form) of the Lord, and they are described as follows.