FACTS AND FACTORS OF DEVELOPMENT 37 



things are manifested by germ cells, but as de- 

 velopment advances each of these functions be- 

 comes more specialized, more complicated and 

 more perfect. A cell which at an early stage 

 was protective, locomotor and sensory in func- 

 tion may give rise to daughter cells in which 

 these functions are distributed to different 

 cells; cells which at an early stage were sensi- 

 tive to many kinds of stimuli give rise to 

 daughter cells which are especially sensitive to 

 one particular kind of stimulus, such as vi- 

 bration, light, or chemicals. 



Functions develop from a generalized to a 

 specialized condition by the process of "physi- 

 ological division of labor" which accompanies 

 morphological division of substance. But just 

 as in the development of structures new parts, 

 which were not present in the germ, appear by 

 a process of "creative synthesis," so new func- 

 tions appear in the course of development, 

 which are not merely sorted out of the general 

 functions present at the beginning, but whicli 

 are created by the interaction and synthesis of 

 parts and functions previously present. 



Much less attention has been paid to the de- 



