30 Life and Love. 



single-celled creatures, where all the functions of 

 life were performed by each cell, these complex 

 forms give rise to cells which do not perform all 

 of the life functions, but only part of them. Thus 

 in the higher animals and plants certain cells are 

 set apart to perform certain functions, and these 

 cells are freed from all other duties. 



In our own bodies, for instance, the muscle cells 

 do all the movint^. The bone cells, the nerve cells, 

 have no power of motion ; only as the muscles 

 move them do they change their place. 



The nerve cells, on the other hand, have con- 

 fided to them the power of sensation and of direct- 

 ting the motion of the muscles. 



So each kind of cell has its special work, which 

 it does for the whole community, thus relieving all 

 other cells of the necessity of doing that special work. 



This division of labor, however, does not prevent 

 the relation between the different kinds of cells 

 from being very close. On the contrary, the rela- 

 tionship is so close that if an accident happen to 

 one cell or one set of cells, all the rest of the body 

 may suffer because of it. 



Where there is this division of labor among the 

 cells of the body, reproduction cannot involve the 

 whole creature, as it sometimes does when the 

 whole creature consists of but one cell. 



Consequently all liigher forms of life close their 

 career in death, their physical life continuing only 

 through their offspring. 



