. Carnegie Institution of Washington publication. ^ 126 Papers from the Marine Biological Laboratory at Tortugas. The first of these methods was tried at the Tortugas laboratory on the eggs of the sea-urchin Lytechinus {Toxopneustes) variegatus. Advantage was taken of the fact that the electrolytes of the eggs and the medium dissociate into ions which bear electric charges, and therefore their move- ment through the eggs could be detected, with a high degree of accuracy, by the electric conductivity method of Kohlrausch.^ Several bushels of sea-urchins were collected each day and the eggs of t
. Carnegie Institution of Washington publication. ^ 126 Papers from the Marine Biological Laboratory at Tortugas. The first of these methods was tried at the Tortugas laboratory on the eggs of the sea-urchin Lytechinus {Toxopneustes) variegatus. Advantage was taken of the fact that the electrolytes of the eggs and the medium dissociate into ions which bear electric charges, and therefore their move- ment through the eggs could be detected, with a high degree of accuracy, by the electric conductivity method of Kohlrausch.^ Several bushels of sea-urchins were collected each day and the eggs of the ripe females placed in large dishes of sea-water. The mucus egg membranes (jelly, zona pellucida) were washed off and the eggs were intro- duced into a conductivity vessel made especially for the purpose (fig. i). The conductivity vessel was placed in the centrifuge and the eggs were precipitated until they were closely packed together. By microscopic examination it was found that only a trace of sea-water was left in the spaces between the eggs (fig. 2). By raising the electrodes above the level of the eggs they came to lie in the supernatant sea-water that had been pressed out from between the eggs. In this way the conductivity of sea- water and egg-mass could be measured separately within two minutes. The conductivity of the egg-mass, when moderately centrifuged, was about one-twentieth of that of the sea-water, in- dicating that the conductivity of the egg itself must be almost nil. The conductivity of the egg-mass was greatly affected by the degree of packing. However, the vessel was so long and narrow that the packing of the eggs could be recorded accurately by mark- ing their upper limit on the side of the vessel (fig. I, a). The eggs could then be removed from the conductivity vessel, replaced, and centrifuged to the same level, when the con- ductivity was found to be the same. In this Fig. I. Fig. 2. way I was able to measure the conductivity before and after fertil
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