Chick development provides a clear model of early vertebrate development and body formation.

The ovum enters the oviduct, fertilization occurs, coverings are added, and the shell is formed in sequence.

Fertilization normally occurs inside the female reproductive tract as the ovum enters the oviduct.

The female reproductive tract secretes accessory coverings as the egg travels through the oviduct.

The shell is secreted in the shell gland, also called the uterus.

Continued development requires egg temperature to remain nearly up to the mother’s body temperature.

A recap connects internal fertilization, coverings, shell secretion, and warm incubation.

The lesson closes with the developmental principle of ordered stages, specialized locations, and necessary conditions.