78 MAN, THE ANIMAL 



the egg cell and sperm cell. In so far as the parts 

 are concerned, the two are equivalent. Each has 

 a nucleus and each has cytoplasm. But when one 

 asks, are these two dissimilar looking cells equiva- 

 lent, the answer must be no. Upon this point 



Figure 24. Diagram to show in outline some of the changes 

 that the egg passes through in preparation for fertilization. 

 The first division results in the formation of a small cell and a 

 large cell. The small cell is called a polar body. Later it 

 divides. At the same time the larger cell or the egg cell gives 

 off a second polar cell. In the giving off of these two small 

 polar cells, there is a reduction in the chromosomes. The three 

 polar cells play no part in the development of the embryo. 

 They are discarded and die. After these elaborate changes, the 

 egg can be fertilized. 



there is general agreement among scientists. To 

 make this clear, the following details are neces- 

 sary: 



Before the egg and sperm can unite in fertiliza- 

 tion, the egg passes through an elaborate prepara- 



