516 THEOPHILUS S, PAINTER 



move, we should expect that the rays would bend more or less 

 uniformly backwards from these points, certainly, under no cir- 

 cumstances would they bend forward and then backwards. The 

 latter conditions could only come about when some region outside 

 of the centrosphere was the first to move. And, if we may 

 judge from the rays in the spiral aster eggs, the areas of move- 

 ment are here situated about a third of the ray's length from the 

 centrosphere. It is only by assuming this that we can under- 

 stand the reason that the rays run forward and then backwards. 

 With two areas in the protoplasm moving, the rays would be 

 pushed forward in these regions and the centrosphere would be 

 dragged along, carried simply by the protoplasm. In the re- 

 gions where the protoplasm was not so actively moving the rays 

 would bend uniformly backwards. That this is the true state of 

 affairs, a careful examination of the figures will show. 



What part the new division centers play in this shifting proc- 

 ess, we are unable to say. That the movement is coincident 

 with the division of the centrioles is clear, but whether the one 

 is the cause and the other the effect, or whether they are both 

 the effect of some common cause, is a question upon which the' 

 present work throws no light. 



A second point of interest lies in the relation between the new 

 and the old rays, for, with the division of the centriole in the 

 monaster we have the formation of new rays, as figure 9 will 

 show. It is in this respect that the conditions in the monaster 

 and in the normal eggs are different. In the normal eggs at the 

 time when the centrioles divide and go apart, the radiations from 

 the old aster have become very faint or have disappeared. In 

 the monaster egg, on the contrary, the centrioles may divide at 

 the time when the radiations from the aster have reached 

 their maximum intensity. It is for this reason, I think, that 

 we find spiral asters in these eggs. Following the division of 

 the centrosome new rays appear. They are concealed from view 

 by the highly developed rays of the old aster. When the new 

 centers shift their positions, the old rays tend to retard the move- 

 ment and thus we get the peculiar figures decribed above. 



A further question of interest is, what significance has the 

 shifting of the spindle in the monaster eggs? The answer is 



