OBSERVATIONS UPON AMPHIBIAN DEUTOPLASM AND ITS RELATION TO EMBRYONIC AND EARLY LARVAL DEVELOPMENT 1 ARTHUR N. BRAGG (From the Zoological Laboratory of the University of Oklahoma} During early ontogeny, several distinct morphogenic processes proceed more or less synchronously whereas others tend to alternate (Richards, 1935). In the exponential period, described by Schmal-hausen (1930), mitotic activity dominates; but with the onset of gastrulation, the mitotic rate falls in close correlation with an increase in differentiation (initiation of the parabolic period). It is at this time, just as the primary caudo-cephalic axis is about to be laid down, that the first embryonic organizers become evident in the dorsal blastoporal lip (at least in Amphibia) and also that important mitotic centers are set up which feed cells into specific regions where they later differentiate into various anlagen, in some cases, at least, under the influence of induction (Derrick, 1937; Self, 1937; Bragg, 1938; Jones, 1939). Behind these more or less morphological manifestations are the actions of the genes, inductors, possibly hormones, etc. which, working through the visible morphological configurations of the cells or their parts, actually are the basic underlying factors in the produc-tion of the embryo, and hence of the adult body. From these considerations, it is evident that the basic factors in embryonic development are essentially physiological, rather than morphological, in character. Studies of cell-migrations or of mor-phogenic movements (Vogt, 1929; Wetzel, 1929; Graper, 1929; Pasteels, 1936; etc.), or mitotic indices (Minot, 1908; Self, 1937; Derrick, 1937; Bragg, 1938; Jones, 1939, etc.), and all similar attacks upon the problem of embryological organization cannot, each method of itself, explain morphogenesis. Such studies are valuable mostly as indicating changes in the morphological configurations of parts which in turn are indirect evidences of the basic physico-chemical changes in the protoplasm, a detailed understanding of which can only be at-tained by physiological methods. Sometime in the future, therefore, we may expect a synthesis of the observations made by the various methods now in use wherein the relationship between cell division, and 1 Contribution from the Zoological Laboratory of the University of Oklahoma, No. 199. 268
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