THE CELL AND PROTOPLASM. 



material in distinction from the rest, which is 

 active material. Inside this vesicle is contained 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 jellylike 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 microscope 

 similar to the cell sub- 

 stance in character, 

 and has frequently 

 been described as a bit 

 of the cell substance 

 more dense than the 

 remainder. Lying 



within the nucleus 

 there are usually to 

 be seen one or more 

 smaller rounded bod- ^S^SS'StaSSLTVS 

 ies which have been nucleus, 

 called nucleoli. From 



the very earliest period that cells have been 

 studied, these three parts, cell wall, cell sub- 

 stance, and nucleus have been recognized, 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 composed of cells. This can 

 best be understood by referring to the accompany- 

 ing figures. Figs. 10-14, for instance, show the 

 microscopic appearance of several plant tissues. 



