Diagram how an animal zygote

becomes a gastrula.

Zygote. Zygote, fertilized egg cell that results from the union of a female gamete (egg, or ovum) with a male gamete (sperm).

Explanation:

Formation of Gastrula. Once an egg is released from the ovary during ovulation, it meets with a sperm cell that was carried to it via the semen. These two gametes combine to form a zygote and this process is called fertilization. The zygote then begins to divide and becomes a blastula.