20 AN INTRODUCTION TO ZOOLOGY. 



with also a little sulphur, and traces of phosphorus ; 

 thesp are believed to be united iu a very complex 

 manner. In the living state it is believed to be 

 likely that the very complex body protoplasm is further 

 united chemically with the inorganic salts which in 

 the dead state are obtained from it, when burnt, in 

 the form of ash, and probably also with various 

 organic substances. The living protoplasm is also 

 full of fat granules, too minute to be dissociated from 

 it for the purposes of analysis. 



The whole of the animal body consists of a basis of 

 this soft, half-fluid jelly-like substance, made up of 

 cells, each with a separate life, activity, and set of 

 movements of its own, and a firmer centre or nucleus, 

 round which it is gathered. Thus the body of an 

 animal (or plant) consists of a myriad of little units, 

 each with a life of its own. One of them may die, 

 and the others will take no harm : one of them may 

 divide, and give rise to several new ones, without the 

 rest being affected thereby. Since the name " cell " 

 is a misnomer, because only the vegetable cell presents 

 any hollowness, and that not always, it has been pro- 

 posed to call the cells plastids. 



Many cells have not only a nucleus, but inside the 

 nucleus again another dot, believed to be yet again 

 ■of darker and firmer material. This is called the 

 nucleolus : it is present in cells which are preparing 

 for very active growth, and in nerve-cells. When a cell 

 is strong and vigorous, its rapid growth makes it 

 necessary for it to divide, otherwise it would become 



