The document describes key stages in embryonic development of chickens before and during incubation. It outlines the formation and appearance of major organs and structures over the first 21 days of development, including the formation of the heart, legs, wings, beak, egg tooth, feathers, and hardening of scales and claws. By the 20th day, the yolk sac is completely drawn into the body cavity and the embryo occupies most of the egg, and by the 21st day, hatching of the chick occurs.