8 THE STORY OF THE BACTERIA. 



But soon, as if in response to the growing 

 needs of the animal, certain of the cells devel- 

 oped a special apparatus, and a special capacity 

 for performing rapid movements, and this ca- 

 pacity was associated with changes in the form 

 of the cells, a specialization 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 physiological 

 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 amceba 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 ; Amceba 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 amceba does not possess, the 

 primitive assimilating power would simply be 



