CELL-ORGANS OF SEA-URCHIN EGG 567 



achromatic body, is gradually vacuolized, and, after formation 

 of chromosomes and breaking up of the germinal vesicle, is finally 

 dissolved in the cytoplasm. The part of the chromatin, emitted 

 by the nucleus, is distributed to the cytoplasm in the form of a 

 diffuse substance. It is difficult to say, whether there is a full 

 analogy between the diffuse chromatin found in the cytoplasm 

 by Schaxel, and the precisely outlined accumulations of the baso- 

 philic substance in my preparations. If the origin of these sub- 

 stances seems to be similar, the fate of the basophilic accumula- 

 tions in my preparations is different from that conceived by 

 Schaxel for his Kinetochromatin. One will remember, that 

 Schaxel admits a gradual exhaustion of the chromatin in the 

 cytoplasm during cleavage. 



One of my next problems will be the study of the origin of the 

 basophilic chromatic accumulations in the cytoplasm. The 

 present study is limited to the conditions exhibited by the ma- 

 ture egg. Here a small, spherical, more lightly stainable area 

 of the protoplasm is differentiated into the nucleus. Its almost 

 homogeneous structure is difficult to determine. The state- 

 ment of Wilson, that ''the terms nucleus and cell body should 

 probably be regarded as only topographical expressions, denot- 

 ing two differentiated areas in a common structural basis" could 

 not be more exactly applied, than in the case of the mature egg 

 of the sea urchin. While the small nucleus of the mature egg 

 contains only occasionally one or two chromatin-granules (fig. 

 2), the cytoplasm abounds in accumulations of basophilic sub- 

 stance. This substance is stainable by every usual chromatin 

 stain, exactly as are the small chromatin granules within the 

 nucleus. 



The occurrence of a peculiar chromatic substance in the cyto- 

 plasm in the early unicellular stage of a multicellular organism 

 reminds of similar phenomena in the life of unicellular and lower 

 multicellular organisms before and during their multiplication. 

 Thus Bergh in Urastyla and Calkins in Tetraminus both describe 

 in the cytoplasm the presence of numerous chromatin granules, 

 and both find, that during the stage of cell division these chro- 

 matin granules accumulate in the center of the cell, and soon 



