62 REPRODUCTION 



the protoplasm of the egg it looks like a new nucleus. The 

 egg also has its own nucleus; hence the egg is now a cell 

 with two nuclei in it. These two nuclei exert an attraction 

 for each other; they gradually move together through 

 the protoplasm, and finally fuse. 



5. The Union of Egg and Sperm: Its Results. The 

 process described above is called fertilization and is 

 found in practically all the higher animals and plants. 

 In nature it is much like the conjugation described for 

 the lower plants and animals, and may have been 

 developed from it. When the full union of the sperm 

 with the egg has been finished, we have a well nourished 

 cell with a nucleus made up of two parts, coming equally 

 from a male and a female cell. The protoplasm and food 

 of this cell, on which further growth is supported, come 

 almost entirely from the female cell. 



The make-up of this new nucleus is peculiarly 

 interesting and important. The student will recall that 

 the nucleus of the egg, as it ripened, lost one-half of its 

 chromosomes. That is to say, if 2X is the number of 

 chromosomes found in the cells of the body in a given 

 species, these are reduced to X in the egg. The same is 

 true of the sperm nucleus. Therefore, when these two 

 bodies unite, they bring to the union two nuclei of just 

 one-half value so far as chromosomes are concerned. 

 When they unite the nucleus is completely restored to 

 the proper number of chromosomes. Whatever was lost 

 has been restored; and, instead of being from one source 

 only, the new cell has material in it usually coming from 

 two individual and distinct parents. It is now known as 

 a fertilized egg. 



Recall that the forming of the fertilized egg is not 

 reproduction. Reproduction gave the egg and the sperm 

 cell. They were the offspring of their respective parents — 

 two quite different kinds of offspring. The eggs and 

 sperms were male and female individuals. They were so 

 feeble that both of them would have died but for their 



