306 Descriptive Zoology. 



Each cell lives and works, not merely for itself, but for 

 all. In their cooperation these units of a lower order have 

 become so united as to form " a unit of a higher order," as 

 the mathematician expresses it. 



The cell is the unit of structure in animals, and where 

 the cells unite and specialize they form a many-celled in- 

 dividual, in the strict sense of the word, that is, it can- 

 not now be divided without destroying the life of the whole 

 complex individual. 



There is one exception : the egg cells can, and do, live 

 separately. This is their work, to separate from the body 

 as a whole, for the express purpose of growing into new 

 individuals. 



