ABSTRACT
Water is the only constituent of the amphibian embryo that is taken up from the environment in appreciable quantities during the course of development, and at hatching it occupies nearly three times as much space in the embryo as all the other constituents combined. In spite of its small molecular size, however, and its ability to diffuse freely throughout the embryo, water is not uniformly distributed nor is its distribution constant. During the early stages of development, large liquid-filled spaces with low solid content—the blastocoel and archenteron—form between the cells, increasing and decreasing in volume as development proceeds; and although amphibian embryos normally develop in an environment which contains little or no solutes, they can tolerate a wide range of external osmotic pressures. Factors which control the uptake and distribution of water in the embryo may therefore be expected to play an important part in growth and morphogenesis. The experiments described in this paper were undertaken to obtain quantitative information on which to base a study of these factors, in the embryo of Xenopus laevis (Daudin).
