List the stages of the embryonic period of development of chordates.

All chordates have several developmental stages. It all starts with the fertilization of the egg. After fertilization, a zygote is formed. The zygote already has a complete chromosome set. Then there are three stages of development. This blastula is a single-layer embryo, gastrula is a two-layer embryo and neurula is a three-layer embryo. Then the embryo is already formed. In most chordates, at the stage of embryonic development, the chord is transformed into other parts of the body. In humans, the notochord is transformed into intervertebral discs.