EGGS AND SPERMS ^ 57 



This point you must keep in mind. We shall need it 

 to make clear what happens later. The cells of animal 

 bodies have twice as many chromosomes as their ripe 

 eggs have. 



6. Sperms and Their Characteristics. In many ways, 

 as we have seen, the sperms are opposite in their nature 

 from the eggs. The sperms are always minute, even 

 more minute than the smallest eggs. Animal sperms are 

 almost all quite active, 



with an active tail or 



flagellum that drives them 



through the fluid in which 



they occur. Sperms are Figure is. Two examples of animal 



real cells, however. They sperms, very much enlarged. 



have a perfect nucleus, and a delicate supply of protoplasm, 



most of which is in the tail mentioned above. Sperm cells 



vary in shape rather more than eggs. Usually a species 



produces many more of the small sperms than of the 



large ova or eggs. 



7. The Development of Sperms. In development the 

 nuclei of sperms of animals behave just as those of the 

 eggs. If the body cells have sixteen chromosomes in 

 their nuclei, these divide, as sperms are being formed, 

 in such a way that each sperm nucleus gets just eight. 

 As the biologist says, there is a reduction division in 

 the forming of eggs and sperms by which they get only 

 X chromosomes when there are 2 X chromosomes in the 

 cells of the body of the parent organism. The mother 

 cells of the sperms are not large cells to start with. The 

 divisions that produce the sperms take place rapidly and 

 the protoplasm does not grow much in the meantime. 

 Hence the sperms cannot fall heir to much protoplasm, 

 and so are small. 



8. The Reduction Division in Plants. What has just 

 been said about the reduction division in animals does not 

 apply to plants in their formation of eggs and sperms. It 



