104 THE STORY OF THE LIVING MACHINE. 



for union with the male cell, but must first go 

 through a series of somewhat remarkable changes 

 constituting what is called maturation of the egg. 

 This phenomenon has such an intimate relation 

 to all problems connected with the cell, that it 

 must be described somewhat in detail. There 

 are considerable differences in the details of the 

 process as it occurs in various animals, but they 

 all agree in the fundamental points. The follow- 

 ing is a general description of the process derived 

 from the study of a large variety of animals and 

 plants. 



In the cells of the body of the animal to 

 which this description applies there are four chro- 



FIG. 34. FIG. 35. 



FIG. 34. This and the following figures represent the process of 

 fertilization of an egg. In all figures cr is the chromosomes ; 

 cs represents the cell substance (omitted in the following 

 figures) ; me is the male reproductive cell lying in contact with 

 the egg ; mn is the male nucleus after entering the egg. 



YIG. 35. The egg centrosome has divided, and the male cell with 

 its centrosome has entered the egg. 



mosomes. This is true of all the cells of the ani- 

 mal except the sexual cells. The eggs arise from 

 the other cells of the body, but during their 



