102 HEREDITY AND ENVIRONMENT 



we know that the germ cells are exceedingly 

 complex, that they contain many visible units 

 such as chromosomes, chromomeres, plasto- 

 somes and microsomes, and that with every 

 great improvement in the microscope and in 

 microscopical technique other structures are 

 made visible which were invisible before, and 

 whether the particular hypothetical units just 

 named are present or not seems to be a matter 

 of no great importance, seeing that, so far as 

 the analysis of the microscope is able to go, 

 there are in all protoplasm differentiated 

 units which are combined into a system; in 

 short, there is organization. 



5. Heredity and Development. — The germ 

 cells are individual entities and after the ferti- 

 lization of the egg the new individual thus 

 formed remains distinct from every other in- 

 dividual. Furthermore, from its earliest to 

 its latest stage of development it is one and 

 the same organism; the egg is not one being 

 and the embryo another and the adult a third, 

 but the egg of a human being is a human being 

 in the one-celled stage of development, and the 

 characteristics of the adult develop out of the 



