How do chicks develop in the egg?

Answer 1

Chickens form just like other animals, except they do it inside an egg instead of inside a womb. Cells inside the fertilized egg divide and differentiate to form the chick. It requires 21 days for proper incubation of a chicken. During the last few days before hatching, the remainder of the yolk is taken up inside the chick and this is its food source for it's first day or two outside the shell. A shell tooth is formed at the end of the beak, and this allows the chick to break through the shell. The shell tooth disappears soon after the chick emerges.

Answer 2

When the egg is laid, embryonic development has already occurred but usually stops until proper cell (environment) conditions are established for incubation to resume. At first, all the cells are the same, but as the embryo develops, cell differences appear. Some cells may become vital organs; others become a leg or wing.

Shortly after incubation begins, a pointed thickened layer of cells becomes visible in the caudal or tail end of the embryo. This pointed area is the primitive streak, and is the longitudinal axis of the embryo. From the primitive streak, the head and backbone of the embryo develop. The the digestive tract forms; blood islands appear and will develop later into the vascular system; and the eye begins to form. On day 2 of incubation, the blood islands begin linking and form a vascular system, while the heart is being formed elsewhere. By the 44 th hour of incubation, the heart and vascular systems have joined, and the heart begins to beat. Two distinct circulatory systems are established, an embryonic system for the embryo and a vitelline system extending into the egg. At the end of the third day , the beak begins to develop and limb buds for the wings and legs are formed. The chick's entire body turns 90o and lies down with its left side on the yolk. The head and tail come close together so the embryo forms a "C" shape. The mouth, tongue, and nasal pits develop as parts of the digestive and respiratory systems. The heart continues to enlarge even though it has not been enclosed within the body. The other internal organs continue to develop. By the end of the fourth day of incubation, the embryo has all organs needed to sustain life after hatching, and most of the embryo's parts can be identified. The chick embryo cannot, however, be distinguished from that of mammals.

The embryo develops and grows quickly. On day seven, digits appear on the wings and feet, the heart is completely enclosed in the thoracic cavity, and the embryo looks more like a bird. After the tenth day of incubation, feathers are visible, and the beak hardens. On the fourteenth day, the claws are forming and the embryo is moving into position for hatching. After twenty days, the chick is in the hatching position, the beak has pierced the air cell, pulmonary respiration has begun.

After 21 days of incubation, the chick finally begins its escape from the shell. The chick begins by pushing its beak through the air cell. The allantois, which has served as its lungs, begins to dry up as the chick uses its own lungs. The chick continues to push its head outward. The sharp horny structure on the upper beak (egg tooth) and the muscle on the back of the neck help cut the shell. The chick rests, changes position, and keeps cutting until its head falls free of the opened shell. It then kicks free of the bottom portion of the shell. The chick is exhausted and rests while the navel openings heal and its down dries. Gradually, it regains strength and takes its first wobbly steps. The incubation and hatching is complete