When the major axis of the body is present, it signals the beginning of which prenatal developmental stage?

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The major axis of the body is a characteristic feature of the embryonic stage of prenatal development, which occurs from around the 2nd week to the 8th week after fertilization. During this stage, the basic body plan of the developing organism is established, and major organs and systems begin to form. The zygote stage occurs immediately after fertilization, before any major morphological changes occur. The fetal stage, which begins around the 9th week and lasts until birth, is characterized by continued growth and development of organs and systems, rather than the establishment of basic body structures. Teratogens are external agents (such as drugs, alcohol, or environmental toxins) that can cause birth defects or developmental disorders in the developing fetus.

When the Major Axis of the Body Is Present, It