Fourteenth day - embryo gets into position suitable for breaking shell
Sixteenth day - scales, claws and beak becoming firm and horny
Seventeenth day - beak turns toward air cell
Nineteenth day - yolk sac begins to enter body cavity
Twentieth day - yolk sac completely drawn into body cavity; embryo occupies practically all the space within the egg except the air cell
Twenty-first day - hatching of chick