4 08 COMPARATIVE ZOOLOGY 



The sperm cells differ from the egg in being very 

 small, commonly motile, and in that a large number are 

 usually produced from a single primary reproductive 

 cell, while the egg represents the entire primary cell. 

 The union of the sperm cell with the germinal vesicle 

 {fertilization) is the first step in development, and with- 

 out it the egg will not develop normally. 



