FACTS AND FACTORS OF DEVELOPMENT 30 



of the egg are relatively few and simple as 

 compared with the bewildering complexities 

 of the adult, and the best way of understand- 

 ing adult structures is to trace them back in 

 development to their simpler beginnings and 

 to study them in the process of becoming. 



7. Development of Functions. — The de- 

 velopment of functions goes hand in hand 

 with the development of structures; indeed 

 function and structure are merely different 

 aspects of one and the same thing, namely 

 organization. All the general functions of 

 living things are present in the germ cells, viz., 



(1) Constructive and destructive metabolism, 



(2) Reproduction, as shown in the division of 

 cells and cell constituents, (3) Irritability, or 

 the capacity of receiving and responding to 

 stimuli. All these general functions of living 

 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 



