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J. GRAY 



this figure is approached the sides AC and BD will begin to 

 flatten; as soon as .„ is ) I, a definite cleavage furrow will 



result between A and C and between B and D. At the same 

 time the convexity of the surfaces AEB and CFD will increase. 

 If the change in length of the axis AC is dependent upon 

 a change in the distance of one centrosome from the other, 

 then one would expect to find a similar relationship between 

 this latter distance and the sector AB. The following measure- 

 ments appear to show that in a variety of cells the cell begins 

 to be deformed in appearance at the equatorial region when the 

 distance between the asters is about -67 of the sector of that 

 part of the cell lying between the asters, and that the cleavage 

 furrow becomes well marked when the ratio has reached the 

 value -8 or -9. 



Prior to any visible change in the appearance of the cell the 



XY 



ratio r-o is progressively increasing from the beginning of 



the formation of the astral figure ; it then passes through the 

 critical value at which the furrow appears and continues to 

 increase until complete cell-division is effected. 



I 



