EEPEODUCTION 413 



is known as gemmation or budding. It may go on so 

 rapidly that the new cell in turn may put out a bud of its 

 own before it is cut off from its parent, and in that way 

 chains of cells may be produced (fig. 164). 



A more general method of the division of the cell or 

 protoplast is of a highly complicated character, and is pre- 

 ceded by a division of its nucleus. This structure we 

 have seen consists essentially of a delicate network of 

 fibrils of chromatin embedded in a hyaline substance, the 

 whole being surrounded by a more or less well-defined out- 

 line derived from the cell-protoplasm, and known as the 

 nuclear membrane. Associated with it in some cases are 

 two small centrospheres. The process of division, which is 

 known as Karyokinesis, or Mitosis, begins by the network 



FIG. 164. SACCHABOMYCES CEBEVISLE, OB YEAST-PLANT, AS DEVELOPED 

 DUBING THE PBOCESS OF FEBMENTATION. X 300. 



a, b, c, d, successive stages of cell-multiplication. 



of fibrils becoming coarser and gradually separating to 

 form a long coiled fibre. The nucleoli disappear and the 

 nuclear membrane ceases to be distinguishable. At the 

 same time, in those cases in which centrospheres have 

 been seen, they shift their position and come to lie on 

 opposite sides of the nucleus at some little distance from 

 it. The long coiled fibre of chromatin breaks up into a 

 number of pieces, often V-shaped, which point towards the 

 centre of the nucleus. The number of these varies in 

 different cases, but is constant in the successive divisions 

 of an individual. These pieces of the fibre are known as 

 chromosomes. The chromatin in them is broken up into 

 thin discs which are separated from each other by smaller 

 discs of unstainable substance. 



