464 THEOPHILTTS S. PAINTER 



second division cycle shift over into an amphiaster, we find, 

 in the cleavage plane, a swelling of the ectoplasmic layer and 

 changes in surface contour (fig. A) which are similar to, but 

 more severe than, those in normal division. And in those eggs 

 where the monaster persists at the later cycle we have first, the 

 swelling of the hyaline layer, then the movement and then the 

 egg ceases to undergo active changes and resumes its rounded 

 form more or less completely. 



We thus see that the behavior of the monaster eggs, as aber- 

 rant as it appears at first sight, is similar to what we find in 

 normal cleavage, both in the sequence of events and in the 

 expression of the forces at work. And it gives us a far clearer 

 picture of the intensity of the action of these forces, than that 

 which we see in normal cleavage. No one has doubted that cell 

 division was accompanied by changes in surface .tension — any 

 change from the spherical would necessitate this — but the 

 formation of pseudopod-like processes and the general amoeboid 

 movement of the protoplasm, lasting some time and involving 

 a large part of the egg protoplasm, are expressions of a far* more 

 powerful force in cell division than normal cleavage would ever 

 lead us to suspect. 



One striking feature accompanying the protoplasmic move- 

 ment, seen best in pigmented eggs, is the movement of the pig- 

 ment granules (fig. 11). Both in Strongylocentrotus and Ar- 

 bacia the pigment lies in the superficial layers of the protoplasm. 

 During the protoplasmic streaming, in the first monaster cycle, 

 most of this pigment tends to collect in the protoplasmic drop- 

 lets (fig. 11). (This figure is drawn from an Arbacia egg). This 

 fact demonstrates that accompanying the movement there is 

 a flow of the cortical layers of protoplasm of the egg towards 

 the side where the surface changes are most intense. This 

 observation is of extreme interest because a number of authors 

 have described a similar flow of substance toward the cleavage 

 plane in other forms, and a good deal of importance has been 

 given to this as a feature of cell division, i.e., Butschli, and 

 Conklin. A few illustrations will suffice to show how wide- 



