164. HEREDITY AND ENVIRONMENT 



visions by which the germ cells are formed, 

 (c) the particular kinds of egg and sperm 

 cells which combine in fertilization. The an- 

 cestral organization determines all the gen- 

 eral characteristics of race, species, genus, 

 order, phylum. It determines the possibili- 

 ties and limitations of individual variations. 

 Given a certain ancestral organization, the 

 individual peculiarities of the germ cells are 

 determined by the particular character of cell 

 division by which the germ cells are formed, 

 and the peculiarities of the individuals or per- 

 sons which develop from these cells are de- 

 termined in large part by the particular kinds 

 of germ cells which unite in fertilization. 



The behavior of chromosomes in matura- 

 tion and fertilization is like the shuffle and deal 

 of cards in a game, and apparently with the 

 same object, viz., never to deal the same 

 hand twice. To make this comparison more 

 complete suppose that kings be discarded from 

 the pack, leaving 48 cards of two colors, red 

 and black, which we will compare to the 48 

 chromosomes of maternal and paternal origin 

 in the human oocyte ; suppose that in the shuf- 



