458 THEOPHILUS S. PAINTER 



being present in all my material, 2 but whether the difference 

 is due to capricious fixation or staining, or is of morphological 

 significance, I am unable to say. Both types of eggs may be 

 found side by side in the same section. In the one type (fig. 

 16) the center of the centrosphere is more deeply staining, and 

 when one examines the structure under the highest powers, it 

 will be found that this is due to the fact, that the meshes of 

 the reticulum of which the centrosphere is composed, become 

 smaller towards the center (fig. 18). This reticulum in my 

 preparations is continuous with the aster fibers (fig. 18). In 

 monaster eggs of the second type (fig. 17) the net-work of the 

 centrosphere is uniform in size throughout the space so that the 

 whole stains evenly. In other respects, the two types of eggs 

 are alike. The chromosomes lie in a sort of half -shell around 

 the centrosphere and they are always just about the same dis- 

 tance from the edge of the centrosphere (fig. L to I 5 page 472) . 



As the controls finish the first division and enter into the 

 second cycle, the centrosphere of the monaster eggs slowly 

 increase in size. This carries the rays of the aster, with the 

 chromosomes attached, nearer to the surface of the egg. 



About the time half of the controls have divided into four 

 cells, changes begin to appear in the monaster eggs. In part 

 of them the chromosomes, which up to this time have been 

 rod-like, undergo a splitting (fig. 20). This is found in eggs 

 with the clear centrosphere. In the second type of egg, one 

 frequently finds the centriole dividing as is shown in figure 19 

 and the spindle within the centrosphere may be clearly seen. 



After the chromosomes have divided they rapidly approach 

 the edge of the centrosphere, and following this, form little 

 vesicles just as is found in the normal cleavage. At the same 

 time the centrosphere becomes enormously increased in size 

 (figs. 21 and 25) and the rays of the aster reach to the surface 



2 In one series of eggs, I have found, in addition to the two types of monaster 

 eggs, here described, a third which is different and corresponds with the fan- 

 asters ('Flacherkern') of the Hertwigs ('87) and others. Only part of the aster 

 is present and there are only 18 chromosomes present. These eggs are begin- 

 ning parthenogenetic development, but they soon disintegrate. 



