CENTRIFUGING THE EGGS OF ILYANASSA IN REVERSE

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Abstract
The eggs were stratified on the centrifuge in the reverse direction from that which they ordinarily take on the centrifuge if they are held in a solidified gelatin solution. The polar protoplasm is then moved towards or even into the antipolar end of the egg (where the antipolar lobe normally forms), and the yolk of this region is driven towards or into the polar hemisphere. The exchange is not brought about by the lighter and heavier elements passing individually by each other, but the polar protoplasmic material as a whole passes along one side of the egg and the yolk along the opposite side. Many of the eggs do not become completely inverted in the gelatin before freezing it, hence they show the protoplasm along one side and the yolk on the opposite side. In eggs centrifuged "in reverse" before the polar spindle has passed to the pole, the chromatin of the egg and the sperm-nucleus are carried in the protoplasm towardsor into the antipolar hemisphere. Polar bodies often fail then to be given off. Nevertheless the inverted egg may divide, beginning in the region where the segmentation spindle comes to lie. It is significant that the antipolar lobe appears in the inverted eggs even when it contains only the protoplasm and oil of the polar region. Hence the interior of this region is not responsible for the lobe formation.

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