OBSERVATIONS UPON AMPHIBIAN DEUTOPLASM AND ITS RELATION TO EMBRYONIC AND EARLY LARVAL DEVELOPMENT

Abstract

Yolk granules in embryos and early larvae of Bujo cognatus, B. woodhousii, Rana sphenocephala, Scaphiopus hammondii Baird, and Triturus torosus show gradients in size in different types of cells. Micromeres and their derivatives have mostly small granules; macromeres and their derivatives contain mostly large ones. The granules are carried passively in all of the cells during all stages till late in embryonic life. The early increase in size of the embryo is due almost entirely to absorption of water. Yolk is not used till after the fundaments of all the major organ-systems are laid down. Utilization of yolk begins in the ectoderm, particularly in regions first in histological differentiation, mostly dorsal and cephalic in the embryo. Yolk granules stored in the ventral yolk mass are the last to be utilized. All spp. used for this study agree essentially in these matters but Scaphiopus begins the utilization of yolk slightly earlier in ontogeny than any of the others. It could not be detd. whether yolk serves primarily for increase in bulk, as a source of energy, or for both; and no explanation is offered as to the source of energy for the actively katabolic process of cleavage but it is certain that the yolk is not this source.