REPRODUCTION 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. 162). 
A more general method of the division of the cell or 
protoplast is of a highly complicated character, and’ is 
preceded 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 
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Fie. 162,—SaccHAROMYCES pened oR YEAST-PLANT, AS DEVELOPED 
DURING THE PROCESS OF FERMENTATION. x 800. 
a, 6, v, 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 
small portions which are separated from each other by 
smaller films of unstainable substance. 
