Gastrulation is the developmental process, involving extensive cell reorganizations, which results in the formation of the mesoderm and gut endoderm of the embryo. The prefix gastr- in fact means ‘stomach’, which is perhaps both a reference to the shape of the gastrula stage of miolecithal eggs (e.g. sea urchin, Amphioxus) and to the fact that the endoderm, which lines the digestive tube, arises during gastrulation. Its importance was eulogised by Lewis Wolpert's famous statement that ‘it is not birth, marriage or death but gastrulation that is truly the most important time in your life’. Not only does the embryo become trilaminar, but it is also during gastrulation that the basic body plan is laid down, the three axes of the embryo become established and many cells receive the signals that lead them to acquire developmental fates and positional information.

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