STUDIES WITH THE CENTRIFUGE 33 



The structure of the aster 



This brings us to a consideration of the asters themselves. 

 The normal aster (fig. 7) as represented in section consists of a 

 mass of purple staining granules, continuous with and indis- 

 tinguishable from the granules separating the yolk spheres. Even 

 the highest magnification fails to reveal any trace of centrosome ' 

 or astral fibers. There is no radial arrangement apparent in the 

 central mass. The surrounding yolk granules, however, are 

 arranged in quite regular rows, radiating from the purple area 

 and between some of these rows the paths of granules are wider 

 than elsewhere, giving an appearance of rays. But these rays 

 appear to be entirely granular and not to contain fibers. 



The partially centrifuged egg (fig. 1) indicates that there is 

 something stable in the structure of the granule mass, which 

 represents the aster, for the yolk spheres do not move into it, but 

 maintain to some extent their radial arrangement. An egg in 

 which the substances have been well separated (fig. 3) illustrates 

 one of the most peculiar things in the behavior of the aster. 

 Whereas in the normal egg the aster is purple, in the centrifuged 

 egg the aster, lying in the purple hemisphere, is differentiated 

 from the surrounding granules by its yellow stain. It is an irreg- 

 ular disc of yellow granules whose edges fade into the purple. I 

 have tried to demonstrate the presence of fibers radiating from 

 the center of the disc by using orange G, Congo red or eosin with- 

 out any counterstain. But the stains have failed to show any sug- 

 gestion of an astral fiber. The spindle fibers, on the other hand, 

 are visible even with these simple stains though they are not very 

 clear unless haematoxylin is used. In some preparations the aster 

 is homogeneous, in others there is a more or less distinct radial 

 arrangement of the granules with clear spaces between. The 

 latter is, I think, due to poor preservation. 



The same change in staining capacity of the aster is found in 

 eggs centrifuged just before the nuclear walls have broken down. 

 Hence the affinity for the acid dye is not due to the age of the 

 aster. There are present in the normal aster both basic and acid 



The Journal of Experimental Zoology, Vol. 10, No. 1 



