80 THE STORY OF LIFE'S MECHANISM. 



a somewhat transparent semifluid material which 

 has received various names, but which for the 

 present we will call cell substance (Fig. 9, pr). It 

 may be abundant or scanty, and has a widely 

 varying consistency from a very liquid mass to 

 a decidedly thick jelly-like substance. Lying 

 within the cell substance is a small body, usually 

 more or less spherical in shape, which is called 

 the nucleus (Fig. 9, n). It appears to the micro- 

 scope similar to the cell substance in character, 



and has frequently 

 been described as 

 a bit of the cell 

 substance more 

 dense than the re- 

 mainder. Lying 

 within the nucleus 

 there are usually to 

 be seen one or more 

 smaller rounded 



FIG. 9 A cell; cw is the cell wall; pr, Vjn/Kpo whiYh 

 the cell substance ; n, the nucleus. S , , 



been called nudeoli. 



From the very earliest period that cells have 

 been studied, these three parts, cell wall, cell 

 substance, and nucleus, have been recognised, but 

 as to their relations to each other and to the 

 general activities of the cell there has been the 

 widest variety of opinion. 



CELLULAR STRUCTURE OF ORGANISMS. 



It will be well to notice next just what is 

 meant by saying that all living bodies are com- 

 posed of cells. This can best be understood by 



