The Uptake and Distribution of Water in the Embryo of Xenopus Laevis (Daudin)

Abstract

1. The weight in water (reduced weight, or R.W.) of single Xenopus embryos has been measured throughout development at 25°C. and 20°C. using Cartesian diver balances. The R.W. remains constant from laying until the early tail-bud stages, after which it decreases slowly. 2. The density of intact embryos, and of open embryos from which the contents of the cellular cavities have been removed, has been measured at the same temperatures. 3. It is concluded that the observed changes in density are due to the uptake or loss of water from the embryo. 4. The volume changes calculated from the R.W. and the density show that from cleavage until the end of neurulation the volume of the embryo increases more and more rapidly. At the end of neurulation there is a sudden decrease in volume due to the emptying of the archenteron cavity. Thereafter the volume again increases, the rate decreasing again as the kidney becomes functional. 5. The volume of the cells, on the other hand, increases only slowly at first; but after the collapse of the archenteron, it increases more rapidly than that of the embryo as a whole. It is concluded that up to this time the water entering the embryo accumulates first in the blastocoel, then in the archenteron and finally in the cells. 6. An hypothesis that has been put forward to explain these changes in the distribution of water is restated in a quantitative form, and is used to calculate theoretical values for the rate of water uptake by the intact embryo from independent morphological data contained in the normal tables of Xenopus development. 7. Theoretical rates of water uptake based on this hypothesis are compared with the observed volume changes calculated from density and R.W. measurements. 8. The two sets of values are in close agreement and it is concluded that the hypothesis provides an adequate qualitative and quantitative description for some of the morphogenetic changes during early development of X. laevis.