Effect of a Centrifugal Force upon Development and Sex 127 



The first cleavage in all these eggs appeared in the end which 

 contained the pink material. 



It is hardly possible that in these fourteen eggs the pink material 

 and the germinal vesicle were driven in each case to the animal 

 pole. If this assumption is correct these two lots of eggs indicate 

 that the position of the first cleavage is determined by the induced 

 position of the germinal vesicle at either end of the egg. When, 

 however, the germinal vesicle is carried to the side of the egg 

 with the pink material, that is, when it comes to lie midway 

 between the two ends of the egg, it moves later toward one of 

 the ends of the egg since the first cleavage in such cases is at one 

 end. 



Ill RELATION OF THE- FIRST CLEAVAGE PLANE TO THE STRATIFI- 

 CATION OF THE MATERIAL OF EGGS CENTRIFUGED WHEN THE 

 MATURATION -SPINDLE IS PRESENT 



Some of the centrifuged females were found containing eggs 

 stratified into the three characteristic zones but showing the 

 maturation spindle apparently at the side of the egg, where it 

 normally forms, in the clear middle zone (Fig. 2). 



In cases where the pink zone was in the end of the egg toward 

 the head of the animal the first cleavage sometimes appeared in 

 that end of the egg and cut off the pink zone in the small cell. 

 At other times it appeared at the opposite end of the egg and 

 included the gray zone in the small cell. In other cases where the 

 gray zone was in the end of the egg toward the head of the animal 

 the first cleavage sometimes appeared in that end but at other times 

 it appeared in the opposite end of the egg. When the eggs were 

 centrifuged so that the stratification was from side to side, instead 

 of from end to end the first cleavage usually cut off a part of each 

 of the three zones in each cell. 



Apparently the first cleavage appeared at that end of the egg 

 nearest to the maturation spindle irrespective of the stratified 

 zones of the egg. 



