156 THE STORY OF LIFE'S MECHANISM. 



separated from each other and remained inde- 

 pendent. But so long as this habit continued 

 there could be little advance. After a time 

 some of the cells failed to separate after divi- 

 sion, but remained clinging together (Fig. 45). 

 The cells of such a mass must 

 have been at first all alike ; but, 

 after a little, differences began to 

 appear among them. Those on 

 the outside of the mass were dif- 

 ferently affected by their sur- 

 roundings from those in the in- 



Fio. 45. . & , t . ,, . 



A group of cells tenor, and soon the cells began to 

 SKuS? reprf- share amon g themselves the dif- 

 senting 'the first ferent duties of life. The cells 

 taking. m e on the outside were better situ- 

 ated for protection and capturing 

 food, while those on the inside could not 

 readily seize food for themselves, and took 

 upon themselves the duty of digesting the food 

 which was handed to them by the outer cells. 

 Each of these sets of cells could now carry on 

 its own special duties to better advantage, since 

 it was freed from other duties, and thus the 

 whole mass of cells was better served than 

 when each cell tried to do everything for 

 itself. This was the first step in the building 

 of the machine out of the active cells (Fig. 46). 

 From such a starting point the subsequent his- 

 tory has been ever based upon the same prin- 

 ciple. There has been a constant separation of 

 the different functions of life among groups of 

 cells, and as the history went on this division of 

 labour among the different parts became greater 



