PRIMARY FUNCTIONS OF THE ORGANISM 45 



of living matter, has become the special function 

 of a certain class of cells, the so-called germ-cells. In 

 these cells as in other classes we can trace the 

 gradual increase of efficiency and certainly of action 

 of the function through a division of labor. 



Summary. We have seen that the organism, 

 whether simple or complex, may be looked upon as 

 a machine that does certain things ; in other words, 

 " works." The nature of the work that the protoplas- 

 mic machine does sets it off from all others as some- 

 thing unique and (at present at least) inimitable. No 

 machine that man has ever made reproduces itself, 

 repairs itself, or automatically adjusts itself to chang- 

 ing external conditions. These primary functions, 

 however, are carried out with varying degrees of 

 perfection by different sorts of organisms. As a 

 rule the organisms of comparatively complex struc- 

 ture perform these functions as a unit more efficiently 

 than those of a lower grade of organization. This 

 is due to the fact, as we have seen, that the functions 

 are performed by various parts of the whole organism 

 particularly adapted for the purpose. Physiological 

 specialization and structural differentiation come 

 into play side by side as the result of a division of 

 labor. An organism in which this phenomenon 

 has been extensively developed is spoken of as 

 specialized. One, such as Amoeba, in which there is 

 little or no specialization, is called generalized. As 

 a rule this is the criterion by which we estimate the 

 position of a plant or animal in the scale of life. 



