Facts and Factors of Development 59 



zation the complicated organization of the adult arises. Develop- 

 ment is not the unfolding of an infolded organism, nor the mere 

 sorting of materials already present in the germ cells, though 

 this does take place, but rather it consists in the formation of new 

 materials and qualities, of new structures and functions by the 

 combination and interaction of the germinal elements present in 

 the oosperm. In similar manner the combination and interaction 

 of chemical elements yield new substances and qualities which are 

 not to be observed in the elements themselves. Such new sub- 

 stances and qualities, whether in the organic or in the inorganic 

 world, do not arise by the gradual unfolding of what was present 

 from the beginning, but they are produced by a process of "crea- 

 tive synthesis." 



Modern studies of germ cells have shown that they are much 

 more complex than was formerly believed to be the case; they 

 may even contain different "organ-forming substances" which in 

 the course of development give rise to particular organs; these 

 substances may be so placed in the egg as to foreshadow the 

 polarity, symmetry and pattern of the embryo, but even the most 

 highly organized egg is relatively simple as compared with the 

 animal into which it ultimately develops. Increasing complexity, 

 which is the essence of development, is caused by the combina- 

 tion and interaction of germinal substances under the influence 

 of the environment. The organization of the oosperm may be 

 compared to the arrangement of tubes and flasks in a complicated 

 chemical operation ; they stand in a definite relation to one another 

 and each contains specific substances. The final result of the 

 operation depends not merely upon the substances used, nor 

 merely upon the way in which the apparatus is set up, but upon 

 both of these things as well as upon the environmental condi- 

 tions represented by temperature, pressure, moisture or other 

 extrinsic factors. 



4. Heredity and Environment. Unquestionably the factors 

 or causes of development are to be found not merely in the germ 



