THE CELL 77 



undergoes some remarkable changes and is closely in- 

 volved in the formation of the contractile structures of 

 the tail. The existence of cell organs, which have the 

 power of independent assimilation and growth and divi- 

 sion is a fact of great theoretical interest in its bearing on 

 the general problem of cell organization for it is one of 

 the main reasons that have led Boveries, Weisner and 

 many others to regard the entire cell as made up of 

 elementary self propagating units. Besides the active 

 substance, the cell contains various lifeless bodies sus- 

 pended in the meshes of the network. Examples of these 

 are food granules, pigment bodies, drops of oil or water 

 and excretory matters Among the life- 

 less products of the body must be reckoned also the cell 

 wall or membrane by which the cell bodies may be sur- 

 rounded." 



We shall now begin to consider the subject of repro- 

 duction. The cell multiplies by dividing itself into two 

 parts. In this performance the directing center called the 

 centrosome takes charge of the performance and looks 

 after the details to see that the different specialized and 

 skilled workers in the cell body are exactly equally 

 divided. As this colony of skilled workers called the 

 nucleus possesses the knowledge and experience handed 

 down through past ages, it is very important that division 

 be equal, so that each and all of the cells shall be pos- 

 sessed of the same amount of power, knowledge, skill and 

 information. For this reason the centrosome or directing 

 center of the cell takes full charge of this most important 

 act. 



The following illustrations, Figs. 4-5-6, by Prof. Wilson, 

 will show how the performance of cell division looks 

 through the microscope. The first act is division by the 

 centrosome ; next, the skilled workers, scattered pro- 



