216 GENETICS 



Robert Hooke, as early as 1665, had described 

 "little boxes or cells distinguished from one another" 

 which he saw in thin slices of cork, and to him is due 

 the rather unfortunate use of the term "cell" which 

 has survived in biological writings to this day. The 

 reason this term is unfortunate is because walls, which 

 are ordinarily the characteristic feature of any cell, 

 such as a prison cell, are usually the least important 

 part of the structure of a living cell, often indeed 

 being entirely absent. 



3. A TYPICAL CELI, 



A typical undifferentiated cell is represented dia- 

 grammatically in Figure 47. Near the center of the 



Cell wall 

 Cytoplasm 

 Centrosome 

 Nuclear membrane 



Nucleus 

 Chromatin network 



FIG. 47. Diagram of a typical cell. 



cell the nucleus is shown surrounded by a nuclear mem- 

 brane. The nucleus, in common with the enveloping 

 cytoplasm, is made up of living substance called proto- 

 plasm (Hugo von Mohl, 1846), and around the whole 

 there is usually formed a wall or membrane which 



