136 HEREDITY AND ENVIRONMENT 



egg and sperm. In one or the other of these 

 two maturation divisions the pairs of chromo- 

 somes separate along the line of junction, one 

 member of each pair going to one pole of the 

 spindle and the other to the other pole, so that 

 in each of the daughter cells thus formed 

 only a single set of chromosomes is present 

 (Fig. 32 C and D) ; but since the position of 

 the pairs of chromosomes in the spindle is a 

 matter of chance it rarely happens that all 

 the paternal chromosomes go to one pole and 

 all the maternal ones to the other; thus each 

 of the sex cells comes to contain a complete 

 set of chromosomes, though particular indi- 

 vidual chromosomes may have come from the 

 father while others have come from the 

 mother. There is reason to believe that 

 homologous chromosomes show general re- 

 semblances but individual differences, and con- 

 sequently when the members of each pair 

 separate and go into the sex cells these cells 

 differ among themselves because the individual 

 'chromosomes in different cells are not the 

 same in hereditary value. 



In this way the number of chromosomes in 



