Salt and Water Regulation in the Embryos of Freshwater Pulmonate Molluscs

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Abstract
1. Subjection of 2-cell stages, later cleavage stages and blastulae of Biomphalaria sudanica to anoxia, 1 mM/l. cyanide and a temperature of about 7° C. causes a great swelling of the cleavage cavity and blastocoel. This effect is reversible if the treatment is not too prolonged. 2. Such temporary treatment at early stages has no apparent permanent effect on many of the embryos, but in some the water-regulating mechanism breaks down again at a later stage (postgastrula). The subject may become enormously distended by swelling of the body cavity, and development is halted. 3. Swelling in both (1) and (2) is apparently confined to the extracellular cavities, the cells remaining intact and not obviously swollen. The older embryos subject to delayed swelling (2) can remain in this condition for many days after control embryos from the same mass have hatched. 4. Experiments with 22Na on a delayed swollen embryo suggested that, though water control was seriously impaired, the mechanism for the uptake of sodium into the body cavity was still functioning. 5. The possible significance of these observations in relation to the mechanism for fluid control in the normal embryo is discussed. Many problems remain unsolved and suggestions are made for further work.

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