RATE OF BREAKING AND SIZE OF THE "HALVES" OF THE ARBACIA PUNCTULATA EGG WHEN CENTRIFUGED IN HYPO- AND HYPERTONIC SEA WATER

¹ From the Marine Biological Laboratory, Woods Hole, and the Biological Laboratory, Princeton University

1. Arbacia punctulata eggs, when centrifuged with a force of 10,000 x g, break less readily in hypotonic sea water, and more readily in hypertonic sea water than in normal sea water.

2. When broken apart in hypotonic sea water, the white half is very much larger than the red half. The white half is much larger than the white half obtained by centrifuging in normal sea water, the red half only slightly larger than the red half obtained in normal sea water.

3. When broken apart in hypertonic sea water, the white and red halves are of almost equal size, the white half usually a little smaller than the red half. When broken apart in normal sea water, the white half is somewhat larger than the red half. The white half from the hypertonic sea water is much smaller than the white half from normal sea water, the red half nearly the same size.

4. When the halves obtained by centrifuging in hypotonic sea water are returned to normal sea water, they both lose water, but the white half to a much greater extent than the red half. They become of approximately the same size as though they had been centrifuged in normal sea water.

5. When the halves obtained by centrifuging in hypertonic sea water are returned to normal sea water, they both take up water to about the same extent. The white half remains considerably smaller than when centrifuged in normal sea water.

6. The nucleus of the mature unfertilized egg increases perceptibly in hypotonic sea water and decreases in hypertonic sea water, to a greater percentage volume than the egg itself. It attains normal size on return to sea water.