cells. However, very little is known about 

 these factors and cancer still remains a 

 hideous unsolved riddle. 



Primitive Forms of Mitosis. It is difficult to 

 observe the processes of mitosis in bacteria 

 (p. 601) and blue-green algae (p. 594) because 

 the cells are very small. In many bacteria a 

 single chromosome appears and divides at 

 the time of fission, but whether there is a 

 well-developed mitotic apparatus has not vet 

 been determined. Among the blue-green 

 algae, the chromidial bodies (p. 18), which 

 may represent very small chromosomes, are 

 carefully lined up, divided and separated into 

 two groups that soon are walled off into sepa- 

 rate cells (Fig. 3-6). Among many protozoans 

 (p. 625), definite chromosomes are formed, but 

 the mitotic apparatus lies entirely inside the 

 nuclear membrane, which persists through- 

 out the division (Fig. 3-7). 



IMPORTANCE 



Cell Division in Relation fo Reproduction - 49 



4 2 13 



. 









I* 

 • * 





§•::■ 



* f 





■S, 



Fig. 3-6. Cells of Oscillatoria, a colonial blue-green 

 alga, showing a simple type of mitotic division. 1, 2, 3, 

 4, successive stages of cell division. (Adapted from 

 Olive.) 



SIGNIFICANCE OF MITOSIS 



OF CHROMOSOMES , , .. . ,. a , . , , ,, 



variations of detail in different kinds of cells. 



Viewing the situation as a whole, it especially in the behavior of the nonchro- 



seems clear that the behavior of the matic parts. At every mitosis, each individual 



chromosomes during mitosis is essentially chromosome divides, and one of the two re- 



the same in the cells of all multicellular suiting daughter chromosomes passes to each 



plants and animals — although there are some new nucleus. Such a procedure maintains 



NUCLEAR MEMBRANE 

 _ SPINDLE '■ ■ 



Fig. 3-7. Mitosis in an amoeba. 

 Note that the spindle and chromo- 

 somes lie inside the persisting nu- 

 clear membrane. 



TELOPHASES 



DAUGHTER CELLS 



