Abstract
In a study of the water exchanges of the eggs of the sea urchin, Echinometra lucunter, the appearance of vacuoles was noted during one phase of the swelling process. When single eggs of this species were observed while swelling in 60% sea water, 2 different equilibria were found during each of which the measurements of the egg diameters remained constant for a period of from 20 to 30 minutes. The first of these occurred after approximately 60 minutes' exposure to the experimental solution and the second after 120 minutes, the eggs now exhibiting a somewhat smaller volume. The shrinkage occurring between these 2 equilibria was accompanied by active vacuolization, the vacuoles appearing in the central portion of the egg and migrating to the cortical layer. Although the emptying of these vacuoles to the outside was not seen, it was inferred from the fact that no accumulation of vacuoles could be detected at the periphery even though additional vacuoles were continually migrating in that direction.
Just 1 raised the question whether the consideration of an egg as a simple osmotic system as proposed by Lucké and McCutcheon 2 should not be modified in the light of the wide occurrence of vacuolization in the eggs of Arbacia punctulata. Tests of the capacity of the eggs of Echinometra lucunter to be fertilized and to develop when returned to normal sea water at different times during the swelling process showed that, after the end of the first equilibrium, the eggs no longer react normally. This would indicate that vacuolization only occurs in these eggs after they have been injured and that therefore the normal, uninjured eggs may be considered as simple osmotic systems.
No detailed study of this phase has yet been completed on the eggs of Echinometra so that at this time one cannot explain the mechanism behind this vacuolization.
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