THE CELL ASTER 499 



his conclusions and mine confirm one another rather strikingly. 

 By the centrifuge method Heilbrunn found that after fertiliza- 

 tion the cytoplasmic viscosity rises gradually until it reaches a 

 maximum. It is at this time that the mitotic spindle first makes 

 its appearance. The appearance of the spindle is followed by 

 a gradual decrease in viscosity and the egg cytoplasm returns to 

 its original liquid state. With the microdissection method I 

 was able to locate the gelatinized region in the forming aster. 

 It is significant that Heilbrunn's conclusion, arrived at by using 

 the centrifuge and by noting the effects of reagents which in- 

 crease or inhibit cell gelatinization, and mine, by using the micro- 

 dissection needle, are identical in that one of the factors con- 

 cerned in cell division is a cytoplasmic gelatinization. 



The interior cytoplasm of a marine egg is a viscous fluid. The 

 viscosity is high enough to prevent any Brownian movement of 

 the enclosed granules but low enough to allow of their free move- 

 ment when pushed about with the needle. The transition from 

 the sol to a gel state is gradual. In the formation of the asters 

 the gel state is rigid enough to hold the granules in a compara- 

 tively constant position since strands of the gel are dragged 

 about with the needle. It is, however, much less rigid than solid 

 gelatin which can be cut into discrete non-glutinous masses. 

 It is also very easily reversible, for, in the early aster stage, a 

 slight puncture and tear with the needle will cause it almost 

 immediately to pass back into the sol state. The gel state 

 here is never even visibly an inert solid for one is always con- 

 scious of a very gradual almost imperceptible movement and 

 change. The picture of a gelled strand changes from minute to 

 minute the difference being appreciable as time passes. Living 

 protoplasm even in the gel state, is a dynamic structure never a 

 static one. 



IV. SUMMARY 



1. The sphere is a liquid region free of granules, occupying 

 the center of the aster and increasing steadily in size until the 

 aster reaches full development. 



2. The increase in size of the sphere is apparently due to the 

 accumulation of liquid flowing into the sphere from all parts of 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 23, NO. 3 



