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

¹ From the Zoölogical Laboratory of the University of Oklahoma

Sections of embryos and of larvae of several Amphibia, representing two orders, four families, and five species indicate that the yolk is carried passively in most cells till late in the embryonic period. Just before hatching in most species, but somewhat earlier in Scaphiopus hammondii, disappearance of the yolk begins in the areas of earliest histological differentiation, mostly dorsal and cephalic in the embryo. Since the regions of greatest susceptibility to injury reported by others are often the ones of lowest mitotic rate, it seems probable that histological differentiation is dominated by anabolic, rather than by katabolic, processes, just as growth must be. Similar reasoning shows that embryonic induction in the dorsal lip of the blastopore is also predominantly anabolic. This is indicated by the correlation of the results of four methods of attack; the Getzmässigkeit of Schmalhausen, the mitotic index, studies of cell migration, and differential susceptibility to injurious environments, as reported by various workers, both in Europe and in America.

One interesting result for which no explanation is offered is that the yolk is not used during early ontogeny by any of the forms studied. This leaves no explanation for the source of the energy required by the very actively katabolic process of cleavage. Little if any increase in protoplasmic mass occurs before the yolk begins to be utilized. It is still uncertain whether the yolk serves primarily for increase in protoplasmic mass, for histological differentiation, or for both, since these predominantly anabolic processes proceed concurrently in the late embryonic and larval periods. However, since the process of early embryonic organization and the laying down of most of the fundaments of the major organ systems occur before the yolk is used, it is clear that all of the early morphological manifestations (whatever their individual natures) proceed normally without the aid of the yolk.