122 THE STORY OF LIFE'S MECHANISM. 



surrounded by a membrane and containing a 

 reticulum, a nucleolus and chromatic material, 

 and lastly, a centrosome. Now such an egg is 

 a complete cell, but it is not able to begin the 

 process of division which shall give rise to a new 

 individual until it has united with another cell 

 of quite a different sort and commonly derived 

 from a different individual called the male. Why 

 the egg cell is unable to develop without such 



union with male 

 cell does not 

 concern us here, 

 but its purpose 

 will be evident 

 as the descrip- 

 tion proceeds. 

 The egg cell as 

 it comes from 

 the ovary of the 

 female individ- 

 ual is, however, 

 not yet ready 

 for union with 

 the male cell, 

 but must first 

 go through a 

 series of somewhat remarkable changes con- 

 stituting 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- 



FIG. 33. An egg showing the cell substance, 

 and the nucleus, the latter containing 

 chromosomes in large number and a 

 nucleolus. 



