From the Aitareya-Upanishad

"Out of water he lifted an egg.
He warmed it, and because of His warmth a being with a mouth opened through a crack, for His own form lay within it. From the mouth came speech; from speech fire. A nose appeared; from its nostrils came breath, from breath air. The eyes appeared; from the eyes came sight; from sight the sun. The ears appeared; from the ears came hearing; from hearing the four quarters. The skin appeared; from the skin came hair; from hair vegetation. The heart appeared; from the heart came the mind; from  the mind came the moon. The naval appeared; from the naval came the downward breath Apana; from Apana death. Sex appeared; from sex came seed; from seed water."

And watching the chick hatch, it needed warmth to have the energy to start the move out into the world. First appears the beak, then it peeps, then its nostrils, you can see it panting with the effort. Then its eyes, the whole head, and the final squirm, the whole body breaks loose, the fluff still wet. Not until it is fully born, do we know if it is male or female...