468 THEOPHILUS S. PAINTER 



of the movement. Thus, when the aster retreated well up 

 against one side (figs. 2, 3, 4, 5) the movement was very severe, 

 while, when the aster moved little or none at all (fig. B), there 

 was a very slight movement of the protoplasm. It was pos- 

 sible to explain this fact in one of several ways. Later stages, 

 however, did not support the view that the size or movement of 

 the aster played any part, for the simple reason that, while the 

 aster became often smaller and underwent little or no move- 

 ment (fig. Fi to F s ) the severity of the protoplasmic movement 

 was greater than in the first cycle. 



The nucleus. The nucleus offered less difficulties as a pos- 

 sible source of the protoplasmic movement than the aster. The 

 protoplasmic movement appears always just as the nuclear 

 vesicles are being formed, and the increase in the number of 

 chromosomes at each succeeding division cycle is accompanied 

 by an increase in the intensity of the movement. Again, the 

 fact that the movement is seen only on that side of the egg 

 towards which the chromosomes are directed (in the first mon- 

 aster cycle) points strongly to the latter as being in some way 

 concerned with the movement. And in latter division cycles 

 when the chromosomes cover the aster more or less completely, 

 the formation of pseudopod-like processes involves nearly the 

 whole egg's surface. 



Assuming the nucleus to be the cause of the movement, it 

 would be easy to explain the relation of the aster to it. Cytol- 

 ogists are in general agreement over the fact that the aster 

 tends to exert a solidifying influence over the egg protoplasm, 

 that is, cause the protoplasm within its influence to be less 

 fluid. If this be true then parts of the cell farthest removed 

 from the influence of the aster would be the first to be affected 

 in case some substance was present which altered the surface 

 tension of the protoplasm. In eggs where the aster retreated 

 to one side, the whole opposite side of the egg would be free to 

 move. In case the aster did not retreat, then we should ex- 

 pect to find little movement. Again in eggs, such as monaster 

 eggs of the second or later division cycle, where the aster was 

 small, we should expect to find here the greatest freedom of 

 movement. This corresponds with the observed facts. 



