Certain cells in the body of an animal are set apart very early to become sex cells 

 called gametes. The cells that do this may be called sperm mother cells or e^ 

 mother cells. These divide many times, by mitosis (page 48). Next comes a perioc 

 of growth, when the cells become very large. Then comes reduction division. In- 

 stead of mitosis, the cell splits and only half the number of the chromosomes (pages 

 46 and 396) go with each part. In the male after another division by mitosis the cy- 

 toplasm stretches out into a long motile tail and the mature male gamete is called the 

 sperm. During reduction division in the female, the cell splits into unequal parts,! 

 each taking half the number of the chromosomes. The small structure is called the 

 polar body. As a result of further division another polar body is thrown off; an( 

 the remaining cell becomes a mature egg. Fertilization follows. 



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