The Determination of the Neural Plate in Urodeles

Abstract

An interpretation of recent literature. It is inferred that the determination of neural plate material is a long-drawn-out [process, beginning early in development of the egg, and culminating after gastrulation. It occurs with the changing physiological pattern of the egg. At first the dominant center of this pattern is the animal pole, for which ecto-dermal, mesodermal, and entodermal materials are set apart (but not as yet irreversibly determined). Dominance then passes to the material of the future dorsal lip of the blastopore, where adjacent ectodermal material begins its determination as the neural pre-pri-mordium. This determination increases in definite-ness and completeness as gastrulation progresses and as dorsal-lip material (chorda-mesoderm) comes to underlie the neural pre-primordium. So long as determination is in progress, the egg is regulative, e.g., transplanted regions may differentiate according to their new locations. Hence in this case "regulation" is a primary property, reflecting the mechanism of determination, and assuring that the outcome shall be orderly structure. Temp. differentials applied to the egg while determination is in progress modify the pattern and thus alter the form and position of the neural plate. The determining (inducing) stimuli, which arise from the interaction of regions, are apparently quantitative in nature; specificity of response is supplied by the nature of the material responding.