The head of the embryo grows forward and the gut elongates rearward

The neural folds meet in the brain region, but do fuse

At this stage, four pairs of somites, blocks of mesodermal tissue, have formed

As the head of the embryo grows forward

The head fold further undercuts its anterior end

The neural folds fuse to form new sets

Anterior end develops into a three-part brain

(These rope-like strands, called the chalazae, help to hold the yolk in position)

Early structures of the eye are now prominent

Meanwhile

(The egg passes down the oviduct)

The embryo develops in an equally exciting manner

In its later stage, a small embryo is already visible

(These rope-like strands, called the chalazae)

As a light-colored disk

(Called the blastoderm, the blastoderm)

Soon, blood vessels appear outside the embryo

The heart develops and begins to beat

(Called the chalazae)

The pattern of blood vessels over the egg expands

Supplying the embryo with food and oxygen and removing waste

(Cell division continues and is restricted to the blastoderm)

As the embryo grows, the brain, eyes, and other structures develop

Soon, a vigorously beating heart is pumping blood throughout the complex embryo

Which is rapidly developing into a mature organism

(The cells move from both sides of the midline, a long thickened area called to the center)

Part of the blastoderm, the area pellucida, is translucent because it is over a liquid

And the white of the egg

Vessels over the yolk expands

Some of the albumen becomes thickened and twisted as the egg passes down the oviduct

These rope-like strands, called the chalazae, help to hold the cell in position

The blastoderm at this stage consists of many cells produced by repeated cell divisions

While the egg is still within the organism

(The blastoderm, the area pellucida)

(The head of the embryo grows forward and the gut elongates)

(The neural folds meet)

(The cells move from both sides of the midline, a long thickened area called to the center)