DETERMINATION OF POLARITY BY CENTRIFUGING EGGS OF FUCUS FURCATUS

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Abstract
1. When eggs of Fucus furcatus are centrifuged at 3,000 x g. for 15 or 20 minutes, beginning between 12 and 37 minutes after fertilization, the visible cell inclusions are thrown centripetally (see Fig. 1). 2. Most of the eggs remain visibly stratified until long after the rhizoid protuberances have formed. Ninety-three to ninety-nine per cent of the eggs which remain stratified form rhizoids quite precisely at the centrifugal pole (within 10°; see Fig. 1), even when they have been embedded in random positions in firm agar-sea water before being centrifuged so that they could not orient in the centrifuge in accordance with any earlier polarity. The remainder also form rhizoids on the centrifugal hemisphere of the egg, but farther removed from the centrifugal pole. 3. In eggs which remain stratified, the place of rhizoid origin and the developmental polarity are therefore determined by the axis of centrifugation. This is true regardless of the position in which the stratified eggs are held in agar-sea water during development. If there is an earlier polarity in the egg it is completely supplanted by the effects of centrifugation. 4. In a smaller proportion of the eggs, the cell inclusions have redistributed so completely when the eggs are inspected after the rhizoid protuberances have formed that, in high contrast to the eggs which remainstratified, they are visibly indistinguishable from eggs which have never been centrifuged. Such redistribution is more prevalent when eggs are reared heavy side up in agar than when they are reared heavy side down. The determination of rhizoid formation at the centrifugal pole is lost in inverted eggs which have redistributed. Under the conditions of the experiments, the determination therefore appears to correlate with the distribution of visible inclusions.