Abstract:
The eggs you buy by the dozen at the market are very similar in structure and function to all other bird eggs in the world. Inside the hard shell are the yolk and the white. Several membranes keep various parts of the system separated from each other and from the environment. One additional structure in the egg is easily overlooked—a tiny white mass hardly larger than the head of a pin. This single cell, called the ovum, is the living part of the egg. If the egg is laid by a hen that has not mated with a cock, the ovum will not develop. If the egg is fertile, the ovum will advance through a predictable sequence of dramatic changes that will eventually result in the emergence of a new live bird.

The egg yolk is stored food for the developing embryo and fetus. As the chick advances in size and complexity, the yolk is used up until it is almost totally consumed at hatching time. The egg white (albumen) is composed mostly of water with some dissolved protein (albumin). The primary function of the white is to keep the embryo moist and cushioned during the rigors of incubation.

A more detailed inquiry into the development of an egg and growth of the embryo reveals still more structures and features, all of which are exquisitely designed and complex in function. With amazing frequency they produce the expected outcome—a new chick.

In this review I will focus on structure and physiological of egg formation as well as embryo developments.