Several changes take place during the 18th and 21st days. The abdominal wall surrounds the residual yolk sac on the 19th and 20th days of incubation.
The chick draws what remains of the yolk into its body and "takes its lunch with it" (so-to-speak) when it hatches. Thus, the chick really doesn't need to be fed for the first day or two after it hatches.
Fluid decreases in the amnion. The chick's head is under its right wing with the tip of the beak pointed at the air shell. The neck muscle contracts and forces the egg tooth through the air cell, and the chick takes it first breath. This is referred to as internal pipping. At this time, you may hear the chick peeping inside the shell.
On the 21st day, the chick finishes its escape from the shell. The egg tooth makes the initial break in the shell, a sharp, horny structure located near the top of the beak. This is referred to as external pipping.
The hatching process can last for 4 o 12 hours before the chick completely emerges from the shell. As the chick's head rotates from under the wing, the egg tooth pips the shell and continues to break the shell in a nearly perfect circle from the inside until it is able to push the top off the egg.
The chick, as it appears upon freeing itself from the shell, is wet and very tired. For the next several hours it will lie still and rest. A few hours later the chick, now dry and fluffy, will become extremely active and the egg tooth will dry and fall off.
