Morphogenetic Interactions before Gastrulation in the Amphibian,Xenopus laevis—the Cortical Field

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Abstract
Although the main visible forms of morphogenesis commence at gastrulation it is of great interest to discover whether they are preceded by a series of preparatory changes just as essential to development, although they have no immediately visible effects. When Dalcq & Pasteels (1937) proposed the hypothesis that the cortex and yolk respectively contained morphogenetic factors which determine the main structural features of the embryo, they did not suggest when or how these factors act. I have described a method (Curtis, 1960) for grafting portions of the cortex of the Xenopus egg from one egg to another, and by its use was able to confirm that parts at least of the cortex contain a morphogenetic factor. In the present work this technique has been used to make grafts between the cortex of embryonic cells of varying ages in order to discover whether the cortex alters its morphogenetic properties as development proceeds.
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