CHANGES IN PROTOPLASMIC CONSISTENCY AND THEIR 

 RELATION TO CELL DIVISION. 



By ROBERT CHAMBERS. 



{From Cornell University Medical College, New York City, and the Marine Biological 

 Laboratory, Woods Hole.) 



(Received for publication, July 29, 1919.) 



/. Periodic Changes in Consistency of the Egg Cytoplasm after Fertili- 

 zation and during Cleavage. 



On fertilization an increase in the viscosity of the semifluid cyto- 

 plasm of the sea urchin egg was noticed by Albrecht^ and recently 

 fully demonstrated by Heilbrunn.^ Heilbrunn based his conclusions 

 on his observation that a greater centrifugal force is necessary to 

 stratify the cell constituents of an egg after fertilization than before. 

 P have presented evidence, from microdissection studies on the sand- 

 dollar egg and the egg of Cerebratulus, that the increase in viscosity 

 is associated with the appearance and growth of the aster. 



Upon entrance of the spermatozoon into the egg a diminutive 

 aster makes its appearance as a ball of a jelly-like consistency in the 

 immediate vicinity of the sperm head. This aster, with the sperm 

 nucleus, moves inward as it steadily increases in size until, when its 

 center comes to He in or near the center of the egg, its radiations 

 extend throughout the whole egg. During this migration the sperm 

 nucleus comes into contact with the egg nucleus. The aster then 

 develops completely around the two nuclei, which fuse to constitute 

 the cleavage nucleus. 



The development of the sperm aster in the sea urchin egg is at 

 its height v/ithin 10 to 15 minutes after fertiHzation. This is the 



^ Albrecht, E., Untersuchungen zur Struktur des Seeigeleies, Sitz-her. Ges. 

 Morph. u. Physiol., 1898, xiv, 133. 



2 Heilbrunn, L. V., Studies in artificial parthenogenesis. II. Physical changes 

 in the egg of Arhacia, Biol. Bull., 1915, xxix, 149. 



3 Chambers, R., Jr., Microdissection studies II. The cell aster: A reversible 

 gelation phenomenon. /. Exp'. Zool., 1917, xxiii, 483. 



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