38 THE POPULAR SCIENCE MONTHLY 



ism, 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 chemi- 

 cal elements yield new substances and qualities which are not to be 

 observed in the elements themselves. Such new substances 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 " creative 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 con- 

 tain different "organ-forming substances" which in the course of de- 

 velopment 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. Increas- 

 ing complexity, which is the essence of development, is caused by the 

 combination and interaction of germinal substances under the influence 

 of the environment. The organization of the oosperm may be com- 

 pared to the arrangement of tubes and flasks in a complicated chemical 

 operation ; they stand in a definite relation to one another and each con- 

 tains 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 conditions represented by temperature, pressure, moisture 

 or other extrinsic factors. 



Heredity and Environment. — Unquestionably the factors, or causes, 

 of development are to be found not merely in the germ but, also in the 

 environment, not only in intrinsic but also in extrinsic forces ; but it is 

 equally certain that the directing and guiding factors of development 

 are in the main intrinsic, and are present in the organization of the germ 

 cells, while the environmental factors exercise chiefly a stimulating, 

 inhibiting or modifying influence on development. In the same dish 

 and under similar environmental conditions, one egg will develop into a 

 worm, another into a sea urchin, another into a fish, and it is certain 

 that the different fate of each egg is determined by conditions intrinsic 

 in the egg itself, rather than by environmental conditions. We should 

 look upon the germ as a living thing, and upon development as one of 

 its functions. Just as the character of any function is determined by 

 the organism, though it may be modified by environment, so the charac- 

 ter of development is determined by heredity, i. e., by the organization 

 of the germ cells, though the course and results of development may be 

 modified by environmental conditions. 



