The egg is a complex structure which is built up layer by layer from the inside outwards. The egg follicles mature in the hen’s ovary until they reach the size of a normal yolk. A yolk ball then passes through the funnel into the upper part of the Fallopian tube, where it is surrounded with egg white. The egg in the making then enters the narrow Fallopian tube, where two additional shell skins are added. The air chamber forms between the two membranes at the blunt end of the egg. 

The egg moves further into the Fallopian tube and in the next 20 hours is surrounded with a calcium layer. Shortly before laying the shell cuticle is also formed, which protects the egg from the penetration of foreign matter.&nb