DIFFERENTIATION, HEREDITY, SEX 309 



contain eleven chromosomes, while the other half contain but 

 ten, lacking the idiochromosome. 



Since the nuclei of all the ova contain eleven chromosomea 



FIG. 143. Diagram illustrating the behavior of the X-chromosome during 

 maturation. The X-element is Shown in solid black. The essentials are the 

 same in cases where X is a multiple element, or where it is paired with a Y-ele- 

 ment (see text). 



there are but two possibilities in fertilization. The egg with its 

 eleven chromosomes may be fertilized by a sperm vrth ten, 



