Abstract
The volume of unfertilized eggs of Arbacia punctulata aged in sea water at 19 to 22° C., pH 8.2, is not constant. The volume increases slowly and progressively during approximately the first 23 hours after shedding. The increase in volume of eggs from different females ranges from 1.8 to 3.2%. With further ageing the volume decreases progressively.
Samples of such ageing eggs were placed at successive ages in the same concentration of dilute sea water, at 21.5°, pH 8.2, and the increase in volume of each egg measured during 5 to 7 successive minutes. Nine to 21 eggs were measured at each age. The average of these measurements at each age was plotted and the constant of the curve, i. e., the permeability constant, K, was calculated by the method of Lucké and McCutcheon. K measured the amount of water passing through a unit of surface per unit difference of osmotic pressure per unit time.
The volume of the eggs before immersion in the hypotonic solution was determined in 3 ways: (1) average of 50 measured eggs, (2) by extrapolation, (3) average of all extrapolated Vo values. The permeability constants were calculated by all 3 methods. The results, though varying, all agree in this, that a marked increase in permeability occurs with ageing of eggs.
The increase in permeability was 24.2, 41.0, 43.0, 47.0, and 68% in 5 different experiments, when 50 and 60% sea water was used. In one experiment with 80% solution of sea water the increase was 27%.
There appears in each experiment to be 3 stages in the increased permeability: (1) an initial low rate between 0 and 2 hours after shedding, (2) a higher rate between 3 and about 24 hours, (3) a highest rate between 24 and about 54 hours.
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