English: 1. The embryo turns on its left side. 2. The anterior head region develops further in the same direction, whereas the rest of the body develops oppositely. 3. Bilateral symmetry is regained, but with the anterior head turned around. Note, that the heart (and other organs) retain their original orientation, as there is no evolutionary pressure for internal symmetry.
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Captions
Schema of the development of an axial twist in vertebrates.