Bhashya
यत एवं सर्वभूतानां सारतमम् एतन् रेतः, अतः कानु खल्वस्य योग्या प्रतिष्ठेति स ह स्रष्टा प्रजापतिरीक्षां-चक्रे ।ईक्षां कृत्वा स स्त्रियं ससृजे ।तां च सृष्ट्वा अधउपास्त मैथुनाख्यं कर्म अधउपासनं नाम कृतवान् ।तस्मा-त्स्त्रियमध उपासीत ; श्रेष्ठानुश्रयणा हि प्रजाः ।अत्र वाज-पेयसामान्यक्लृप्तिमाह — स एतं प्राञ्चं प्रकृष्टगतियुक्तम्आत्मनो ग्रावाणं सोमाभिषवोपलस्थानीयं काठिन्यसामा-न्यात् प्रजननेन्द्रियम्, उदपारयन् उत्पूरितवान् स्त्रीव्यञ्जनंप्रति ; तेन एनां स्त्रियम् अभ्यसृजत् अभिसंसर्गं कृतवान् ॥
In plain words
Since this seed is the very essence of everything that lives, Prajāpati asked himself where such a thing could properly rest — and the answer he arrived at was woman. He shaped her, and then he turned toward her in worship: the act of union itself was his worship, offered from below. That is why a man still worships a woman from below — because a child depends on being held in the most excellent place there is. And the text draws out one more likeness here, to the great Vājapeya sacrifice: the organ he made, driving forward with its own motion, stands in for the hard stone that presses out the Soma — both share that same hardness. With it he reached fully across to her, and the two became one.
Close to the Sanskrit
Since this seed is thus the very essence of all beings, [Prajāpati thought]: 'therefore what indeed would be a fitting resting-place for it?' — so did the creator, Prajāpati, reflect. Having reflected, he created woman. And having created her, he worshipped from below — he performed the act called maithuna (union), and named it 'worship from below.' Therefore one should worship a woman from below; for offspring depend on being lodged in what is most excellent. Here the text states the procedure held in common with the Vājapeya sacrifice: he caused this forward-directed organ of his, endowed with a driving motion, his organ of generation — which stands, by its shared hardness, in the place of the Soma-pressing stone — to pass fully across toward the woman's organ; with that he united himself with this woman, forming a union with her.