Egg Structure – The Structure of an Egg

Egg Structure – The Inside Out on the Egg’s Insides!

Chicken EggThe Egg Shell

The first thing you’ll notice is that the egg has a fat rounded end and a pointed cone end. The egg is laid rounded end first. Under the rounded end is the air sack that forms as the contents of the egg cool from the internal temperature of the bird.

The shell itself is slightly porous and allows air to pass through to the interior, whilst still providing protection for the contents from damage and bacteria.


Under the shell are two thin membranes. The first is just under the shell and provides some additional support to the shell. The second surrounds the white of the egg and as the egg ages the two membranes separate. The fact there are two membranes and that they split as the egg ages is why fresh eggs are difficult to peel the shell from when boiled.

Yolk & Chalaza

To hold the yolk in a central position there is a connection of tissue from the membrane that surrounds the yolk to the top and bottom of the second membrane that is technically known as the chalaza. If you crack an egg then you may see a whitish string in the egg white, this is the chalaza.

Egg White (albumen)

Next we have the egg white itself or albumen. In a hen’s egg approximately 60% is white and 40% yolk. In a duck egg, there tends to be more yolk in ratio to white.

The white provides cushioning and additional nutrition for the developing chick and contains less nutrition than the yolk.

Germinal Disc

There’s another membrane surrounding the yolk and then the yolk itself. On the yolk you may see a little white spot, this is the germinal disc which contains the cells that will develop into a chick if the egg is fertile.

Further Articles All About Eggs


Backgarden Chickens & Other Poultry

Backgarden Chickens Poultry Book

Our bestselling book!
More Information

Free Monthly Newsletter