46 



HEREDITY AND SEX 



united (B). Two divisions take place (C, D), when the 

 two polar bodies are formed, leaving seven chromosomes 

 in the egg (E). Each egg contains as a result only one 

 X chromosome. 



Any egg of lygseus fertilized by a sperm carrying an 

 X chromosome produces a female that contains two 



OncopettcLJ S 



lO 



t°.» 



B 



•o°' 



At«too9tt 



'oo, 



Fig. 25. 



^^ 



Z's or XX. Any egg fertiUzed by a sperm containing 

 a Y chromosome produces a male that contains one 

 X and one 7, or XY. 



Another insect, Oncopeltus fasciatus, represents a 

 third type in which the chromosome groups in the 

 male and in the female are numerically aUke and alike 

 as to visible size relations. 



