FACTS AND FACTORS OF DEVELOPMENT 83 



and purely hypothetical external forces; the 

 one placed all emphasis upon the germ and its 

 structures, the other upon outside forces and 

 conditions. 



3. Preformation and Epigenesis. — Modern 

 students of development recognize that neither 

 of these extreme views is true — adult parts 

 are not present in the germ, nor is the latter 

 homogeneous — but there are in germ cells 

 many different structures and functions which 

 are, however, very unlike those of the adult, 

 and by the transformation and differentiation 

 of this germinal organization the complicated 

 organization of the adult arises. Development 

 is not the unfolding of an infolded organism, 

 nor the mere sorting of materials already pres- 

 ent in the germ cells, though this does take 

 place, but rather it consists in the formation 

 of new materials and qualities, of new struc- 

 tures and functions — by the combination and 

 interaction of the germinal elements present in 

 the oosperm. In similar manner the combina- 

 tion and interaction of chemical elements yield 

 new substances and qualities which are not to 

 be observed in the elements themselves. Such 



