The egg is also a consumer package and this function requires subtle differences in the construction of the eggshell. To meet these functions the bird constructs the egg to a blueprint, which permits maximum contact between the shell and the soft membranes onto which the shell is deposited. Every shell will display variation from the norm with respect to its structural integrity but it is when the variations become overt that problems ensue. The eggshell is a multilayered structure. The shell membranes consist of a web of interlacing fibres.
Calcium salts seed onto the outer shell membrane fibres.
This basal crystal layer, and the crystals which radiate from it, constitute the mammillary layer. Continued crystal growth gives rise to the palisade layer and the vertical crystal layer. The shell is then covered by a cuticle.