482 THEOPHILUS S. PAINTER 



inspection of figures Hi and H will show that in all these cases 

 the distance between the edge of the centrospheres and the 

 chromosomes remains about the same. 



This relation between the chromosomes and the edge of the 

 centrospheres is retained until the chromosomes begin to split. 

 As soon as division begins, the chromosomes rapidly approach 

 the edge of the centrosphere (figs. H e to HU). 



A close study of the dividing chromosomes shows that the 

 splitting takes place in one of two ways. Sometimes we find 

 a clear line appearing between the two halves (fig. G 2 ) which 

 separate more as they approach the centrosphere. More 

 usually, however, the splitting is accompanied by a twisting 

 of the two halves (fig. G 2 ) about each other and the formation 

 of V-shaped figures. In either case, both halves retain their 

 attachment to the same fiber, and this condition persists until 

 the chromosomes have reached the edge of the centrosphere, 

 in the vast majority of cases. Here and there, however, the 

 two halves appear to be attached to different fibers, as they ap- 

 proach the sphere. 



While no light can be thrown on the cause of the chromo- 

 some division, it should be pointed out that it appears entirely 

 independent of the condition of the aster. The latter may be 

 large or small, round or sunken in, or the centrioles may even 

 be undergoing division. The chromosomes and the asters seem 

 totally independent in their behavior. 



By carefully measuring the distances between the chromo- 

 somes and the edge of the centrosphere, I have found that this 

 is approximately the same in all monaster eggs in which the 

 chromosomes are undivided. There is no sign of any move- 

 ment of the chromosome until a split appears. Then the ap- 

 proach to the edge of the centrosphere is very rapid and few 

 intermediate stages can be found. The division of the chromo- 

 somes seems to give the necessary stimulus which causes them 

 to approach to the centrosphere. 



This fact that no movement of the chromosomes takes place 

 until after they have divided has an interesting bearing on the 

 question of the forces at work here. As is well known, a num- 



