32 GEORGINA B. SPOONER 



lying at the end of the sac, is nearly spherical and the action of 

 the force has been such as to broaden the cell in the direction of 

 the layers. There is, therefore, plenty of room for the spindle to 

 lie straight. In (b) and (c), however, the already elongate and 

 flattened eggs were, if anything, more elongated and consequently 

 flattened by centrifuging and the spindle has been forced into a 

 position with its axis in the shortest diameter of the cell. Since 

 this diameter is shorter than the normal length of the spindle, 

 the spindle must bend. 



Egg (c), in which one aster lies nearer the yolk than the other, 

 suggests what the normal position of these spindles may have 

 been, for their position in the short axis of the cell is proof that 

 there has been more than a simple shifting of the karyokinetic 

 figure to one side. The egg is so much flattened that the diameter 

 of the egg perpendicular to the plane of the section is probably as 

 long as the diameter perpendicular to the stratification. If the 

 spindle had lain normally in the former position the natural 

 result of centrifuging would have been a simple shifting to one 

 side of the spindle, in which case an equatorial plate would have 

 shown in the section instead of the longitudinal view of the spindle. 

 If, however, its original position were perpendicular to the laj^- 

 ers, it would shift as a whole to the centripetal pole. The yolk 

 spheres in their passage would drag the centripetal aster back, 

 thereby bending the spindle. The pressure of the yolk spheres 

 being greater in the short than in the long diameter of the cell 

 would cause the aster to be dragged in that direction and account 

 for the spindle's abnormal position in the short diameter of the 

 cell. Such a condition in process is shown in fig. 1, where the 

 egg was not centrifuged completely as shown by the fact that the 

 yolk spheres are not driven completely to. the centrifugal pole. 

 The spindle is only partially bent and one pole is still embedded 

 in yolk. In fig. 3 (c) the process is nearly complete. One pole, 

 however, is still nearer the yolk layer than the other. With 

 longer centrifuging the asters would, probably, assume a sym- 

 metrical position with regard to the layers. 



