Basis of Sex Determination 201 



chromosomes remain constant in number in all cells, 

 the consequence is that all the cells of a female Protenor 

 have two X chromosomes; while all the cells of a male 

 Protenor have only one X chromosome. 



Before Fertilization 



Eggs 



Sperm 



After Fertilization 

 Fig. 39 



The chromosome situation in Protenor is a somewhat 

 extreme case, inasmuch as one X chromosome is 

 entirely lacking in the male. In other forms of Hemip- 

 tera, e. g., Lygceus, there are also two types of spermato- 

 zoa appearing in equal numbers differing in regard to 



