THE CHROMOSOMES 65 



to the development of a new individual. It merely in- 

 creases in quantity by the absorption and assimilation 





i &^n 



Drawing by A. B. Stout 



FIG. 13. Cells of sedge (Carex aquatilis), greatly magnified. Stages of cell division 

 (mitosis), an equal amount of ckromatin going into each of th'e two cells. 



of food, while the number of cells is increased by divi- 

 sion. When the proper time comes, the germ cells go 

 through a peculiar process known as maturation, 

 whereby they are made ready for fertilization, and the 

 consequent origin of new individuals. In ordinary cell 

 division (called mitosis) the chromosomes divide, so that 

 each resulting cell gets half, and has the same number 

 of chromosomes as the mother cell. In the maturation 

 divisions something different occurs. The sperm cells 

 are formed by a division in which half the chromosomes 

 go into one cell, half into another. There is no division 

 of the individual chromosomes, such as occurs in mitosis. 

 When there is an odd chromosome, one of each pair of 

 sperm cells has it, the other is without it. The matur- 

 ing egg cell, on the other hand, finally throws off a 

 minute particle known as a polar body. This is formed 

 by a division of the nucleus, in which half the chromo- 

 somes remain, while the other half pass into the polar 

 body. Thus the egg cell, too, comes to have only half 



