Cell Division 



93 



Fig. 12. Mitosis in a living blastomere of the whitefish Leucichthys artidi (Spencer Phase Contrast, dark 



medium). 



and the process can be followed in the phase 

 microscope. The anaphase in such a cell is 

 shown in Fig. 12. In addition to chromo- 

 somes the outline of the spindle is clearly 

 visible in the living cell, and sometimes even 

 details such as the centrioles, chromosomal 

 fibers and aster-rays (Fig. 12C). 



Many other cells of plants and animals 

 have been used to study mitosis in the living 

 cell. With the phase microscope many struc- 

 tures are now visible in life that before were 

 known only from fixed and stained prepara- 

 tions. Photographs of a variety of living cells 

 in division have been published (Table 2). 



ANALYSIS OF MITOSIS 



After this brief description of a cell in 

 division we shall now look at some aspects 

 of mitosis in more detail. We can recognize 

 two main events: The division of the nucleus 

 (karyokinesis) and the division of the cyto- 

 plasm (cytokinesis). The nuclear division 

 normally involves duplication of the chromo- 

 some units, the splitting of the chromosome 

 into two equivalent halves (chromatids), 

 their condensation into compact bodies, and 

 a series of chromosome movements resulting 

 in the distribution of the chromosome halves 



