STUDY OF CELL MECHANICS 481 



egg where the aster retreated part way to the surface. Here 

 the protoplasm released from its control is free to undergo a 

 certain amount of movement and finally, in those commonest 

 cases in which the aster moved until it lay well up against one 

 side (fig. 1, etc.) the movement was most severe. 



Undoubtedly the severe movement of the protoplasm during 

 the change of monaster eggs (figs. Ai and A 2 ) is due to the same 

 cause. As I have pointed out, the spindle usually lies some- 

 what excentrically in these eggs with the result that the side 

 farthest removed from the spindle shows the greatest amount 

 of surface tension change. And in those eggs in which the 

 monaster appears at the second division cycle, the severe move- 

 ment, while due, perhaps to some extent to the increased num- 

 ber of chromosomes, is also to be correlated with the feeble de- 

 velopment of the astral system. 



These facts taken together with the evidence from the nar- 

 cotized eggs point unmistakably to the asters as regulative 

 centers during cell division centers, which determine the chan- 

 nels in which the second factor will operate. 



BEHAVIOR OF THE CHROMOSOMES 



A number of authors (Boveri, M. Boveri, Wilson et al.) have 

 pointed out that monaster eggs demonstrate that the chro- 

 mosomes do not require two opposing centers to pull them 

 apart in order for them to divide and separate; the process is 

 autonomous. A close study of the behavior of these bodies 

 reveals several points of interest. 



When the chromosomes become scattered over one side of 

 the aster, they all come to be at about the same distance from 

 the edge of the centrosphere (fig. HO and are attached to it by 

 means of fibers. The relation is established very early, and, 

 corresponds to the equatorial plate phase of normal division. 

 Following this, the aster undergoes a slow increase in size (figs. 

 H 2 to H 4 ) which causes the edge of the centrosphere to approach 

 nearer to the periphery of the egg. The chromosomes are 

 carried along on their fibers, so that they come to be farther 

 and farther from the middle of the centrosphere. A close 



