Ultrastructure of vitelline membranes from normal and mottled egg yolks.

This study showed that ultrastructure of the vitelline membrane degenerated with degree of yolk mottling. The more severe the mottling the greater the damage to the membrane. The vitelline membrane appears to be composed of three separate structures. The primary matrix (probably collagen) retains its composition until mottling is most severe; then this structure starts to come apart and lose its integrity. The secondary matrix (probably mucin) aids in holding the primary structure in a fixed position. When this structure is removed there is movement in the primary matrix causing large holes to appear. The tertiary matrix (also mucin) is the quickest to disintegrate. The tertiary matrix covers the other structures much like the cuticle around the egg shell. Once it is removed, the remaining structures are open to stress and damage as mottling increases.