It is generally believed that the foregut in the chick embryo is induced by the mesoderm (Waddington & Schmidt, 1933; Waddington, 1952). In particular the splanchnic mesoderm is thought to be important (Rudnick & Rawles, 1937; Rudnick, 1952). In normal development the splanchnic mesoderm becomes fused with the presumptive foregut floor whilst the gut is developing and both become considerably thickened. During this period of induction there is a rise in the mitotic rate in this region of the endoderm (Bellairs, 1955). Similarly, Balinsky (1955) reported that the mitotic rate is raised in tissues when they are stimulated to form a limb. He also found that there is a high rate of division in the regions capable of inducing limb development.

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