8.18 अव्यक्तात् from the Unmanifested, व्यक्तयः the manifested, सर्वाः all, प्रभवन्ति proceed, अहरागमे at the coming of day, रात्र्यागमे at the coming of night, प्रलीयन्ते dissolve, तत्र there, एव verily, अव्यक्तसंज्ञके in that which is called the Unmanifested.

Commentary:
When Brahma awakes, all manifestations, moving and unmoving (animate and inanimate) stream forth at the coming of the day from the Avyakta or the Unmanifested. When Brahma goes to sleep, all the manifestations merge in the Unmanifested, for the cosmic night has set in.Coming of the day Commencement of creation.Coming of the night Commencement of dissolution. (Cf.IX.7and8)