Chalaza

The chalaza (plural: chalazae) is a structure within bird and reptile eggs, as well as plant ovules, that suspends the yolk or nucellus within the albumen or ovule cavity. It appears as one or two spiral, rope-like strands of opaque white material.

Function:

In bird eggs, the chalazae's primary function is to keep the yolk centered in the egg, preventing it from drifting and adhering to the shell. This centering is crucial for proper embryo development. The chalazae act as anchors, attaching to the shell membranes at either end of the egg. As the egg rotates, the chalazae untwist and twist, allowing the yolk to remain relatively stable. The more prominent chalaza is usually located at the pointy end of the egg.

In plant ovules, the chalaza is the basal part of the ovule where the integuments and nucellus are fused. It is located opposite the micropyle. Its function involves nutrient transport to the developing embryo sac and is considered an important tissue in determining the pathways of nutrient flow.

Composition:

The chalazae in bird eggs are composed primarily of protein fibers, similar to those found in the albumen (egg white). These proteins are twisted and compacted to form the ropy strands.

Significance:

The presence of prominent chalazae in a bird egg is often considered an indicator of freshness, although it's not a foolproof method. As the egg ages, the chalazae may become less prominent.

Etymology:

The word "chalaza" comes from the Greek word khalaza, meaning hailstone or lump. This likely refers to the appearance of the chalaza as a small, whitish mass.