Three layers, called the ectoderm, the mesoderm, and the endoderm, form in the developing organism during the period of the

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The three layers called ectoderm, mesoderm, and endoderm form during the period of the embryo, which is the stage of development from fertilization to eight weeks of gestation. The zygote refers to the single cell formed after fertilization, while the amnion and fetus refer to later stages of development after the formation of the three germ layers.

Three Layers, Called the Ectoderm, the Mesoderm, and the Endoderm