b, The effect of shape on the developmental axis of the Fucus egg

The cleavage l)lalie of many cells has been deterniined by artificially imposed elongation. In general the long axis of the division figure comes to lie in the long axis of the cell so that the plane of division is perpendicular to the long axis. The plane and sequence of division of many eggs has been altered in this way, but the primary developmental axis, or polarity, has not been affected. Lindahl (1936) has found, however, that when sea urchin eggs are stretched by passing through capillaries, the first end to enierge tends to beconie ventral (if it is not the animal or vegetal pole) so that in this case the (lorso-ventral axis is determmed, as it also is by centrifuging (Runnström, 1926; Lindahi, 1936). In the Fucus egg, which appears to be more plastic than most animal eggs, the primary axis may l)e determined by centrifuging (Whitaker, 1937, 1938). The experiments to be reported were under taken to test the effect of elongation on the division plane and the de velopmental polarity of the egg of Fucus furcatus. METHOD This species of Fucits is hermaphroditic and fertilization takes place when the egg capsule dissolves and releases 8 eggs into sea water in which motile sperm are present. The time of fertilization of the eggs from a given capsule can l)e observed quite precisely. Immediately fol lowing fertilization the naked egg secretes a film of soft gelatinous ma terial which gradually hardens to form a rigid cell wall. If a recently fertilized egg is gently sucked into a glass pipette of less diameter than the egg, it enters and becomes elongated to an extent which depends on the relative diameters of the egg and the Pil)ette. When it is gently blown out into sea water, the elongated shape is retained, no doubt largely because of the hardening of the cell wall in the elongated shape. Unless the egg is sucked into the l)iPette before the wall hardens, it will not enter