THE CELL DOOTRINB. 133 



being stained. To this youngest centre of bioplasm, 

 the term "nucleoleolus" might not be inappropriately- 

 applied. 



Klein has announced in his recent paper " On the 

 Structure of Cells and ISTuclei " (Quart. Journ. Mi- 

 croscop. Sci., July, 1878), that after very prolonged 

 examination he has arrived at the conclusion that 

 these large particles (nucleoli) are due to one of two 

 things : in some instances they are distinctly thick- 

 enings of the nuclear network of fibrillse demonstra- 

 ted by Frommann and Heitzmann, and confirmed by 

 Flemming, Hertwig, E. Van Beneden, Klein himself, 

 and others, or they are merely due to the shrivelling 

 up and intimate fusion of a part of this network. 



Auerbach supposes that the nucleolus is formed 

 by the aggregation about a centre, of nucleolar sub- 

 stance, which is derived either from the periphery of 

 the nucleus itself or from the inmost layer of cell 

 protoplasm. According to him, nucleoli may also 

 multiply by fission. This division is associated with 

 a movement of the new nucleoli through the nu- 

 clear ground-substance, the cause of which is not 

 understood. ' The reverse, or the fusion of several 

 nucleoli into one, also occurs. Auerbach says also 

 that many facts speak for the identity of nucleolar 

 substance and cell protoplasm. In optical appearance, 

 nucleoli and the substance of young cells agree, and 

 vacuolation may occur in either, large nucleoli being 

 seldom free from clear spaces. Both are amoeboid, 

 the movements in nucleoli having been described by 

 many observers. Lastly, nucleoli have, as Auerbach 

 himself shows, that characteristic of vital protoplasm, 



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