8 The Story of the Bacteria 



thing. But soon, as if in response to the 

 growing needs of the animal, certain of the 

 cells developed a special apparatus, and a 

 special capacity for performing rapid move- 

 ments, and this capacity was associated with 

 changes in the form of the cells, a specializa- 

 tion which signalized its advance to a higher 

 type of existence. 



Just here we come upon the great principle, 

 in a very simple form, upon which the enor- 

 mous differences between higher and lower 

 animals rest, the principle of the physiologi- 

 cal division of labor in cells. The more 

 perfect the individual is, the more elaborate 

 do we find the expression of this principle. 



The difference between the amoeba and the 

 olynthus from our present point of view that 

 which makes of the latter a higher animal than 

 the former is that it has a certain group of 

 cells set apart to do a special thing, to move 

 rapidly; amoeba moves, but not so rapidly 

 nor with such directness. If another group of 

 cells were set apart in olynthus to do the 

 digesting, no new cell powers would be devel- 

 oped which the amoeba does not possess; the 



