Of course, to do that, it needs warmth and moisture which the hen provides, but to actually be born, it must do all the hard work totally by itself. Then, not only must it break free of the egg, it must have certain physiological structures in place for respiration and digestion.

Firstly, let us look at the means by which a chick frees itself from the egg. In order to facilitate hatching, Mother nature has provided the chick with a highly specialised tool with which to break the egg shell. It is a small, pointed attachment on the tip of the upper mandible and is known as a "shell cutter" or "egg tooth". This puts to rest the question of the rarity of hen's teeth, because in reality ALL hens have a tooth (at birth and a few days hence). The chick first breaks into the air sac at the large end of the shell. By raising its the upper mandible, the chick can apply pressure to the shell with its tooth, forcing a crack outwards. This moment is called "pipping". Once this is achieved, the chick rotates itself inside the egg all the while extending the crack in the shell as it goes. Once the chick has turned fully in the egg, and cracked the shell right around (or almost so), it pushes against the shell with its feet forcing the end of the shell away from the remainder with its head and shoulders. Once it has the cap off the shell, the chick pushes itself completely free of the confines of the egg and is born. The tiny shell cutter has served its only purpose and will fall off the beak after a couple of days.

Whilst in the egg, the chick has a self-contained breathing system called the 'allantois". This consists of a fine network of blood vessels within the lining of the egg shell. These are connected to the chick by two arteries and a vein. Once the chick breaks into the air sac before beginning to pip, it begins breathing through its lungs. At this point the chick has two completely separate breathing systems, one within its body and one without. The allantois continues supplying oxygen to the chick right through the hatching process, even though it is now breathing with its lungs. Once the chick separates from the egg, the allantois dries up, breaks free of the chick and remains in the egg shell.

The chick at hatching time also has two completely separate digestive systems. During its foetal development, the chick must receive nourishment from within the egg. This is supplied from the yolk and albumen (egg white). At the onset of embryonic activity, veins spread from the foetus across the surface of the yolk. These are known as "vitelline veins" and serve the purpose of collecting nourishment for the chick.

As the chick at this stage, has no digestive system of its own with which to utilise food, special membranes form at the end of the vitelline veins which digest the food before passing the nutrients into the blood. These membranes extend down into the yolk in folds, giving greater nutrient-collecting surfaces. These folds are called "septa" and give the area of the yolk containing them a different appearance to normal yolk. This digestive system continues supplying nutrients to the chick from the point of initial development to some time after hatching, when the last of the yolk food is absorbed and used. So, unlike the external breathing system which remains in the egg shell, the external digestive system is absorbed into the chick's body at hatching. The last of the nutrients supplied by the vitelline system are sufficient to last the new-born chick for one or two days after hatching.