THE CELL 13 



germ-cells have no important relation to the functional 

 activities which are especially concerned with the indi- 

 vidual existence of the animal. They are clearly in- 

 tended for ultimate separation from the individual and 

 destined to provide for the continuance of the species. 

 In some lower forms of life, the body-cells and germ-cells 

 are not so clearly separated, but in the domestic animals 

 such differentiation is characteristic. The male germ-cell 

 is called the spermatozoon or sperm-cell, and the female 

 germ-cell the egg or ovum. 



15. The ovum. The germ-cell of the female is the 

 egg or ovum (Fig. 3). It is one of the largest cells in the 

 animal body. It is spheroidal in 



, 1 



shape and contains a nucleus or 

 germinal vesicle and within the 

 nucleus a nucleolus or germinal 

 spot and a large amount of pro- 

 toplasm (cytoplasm) surrounding 6 

 the nucleus. In the protoplasm 

 are often distributed numerous 

 masses of material or yolk, the 



function of which Seems to be FIG. 3. The ovarian 



chiefly to nourish the fertilized e ff sm A nucleus ; S ' cyt0 ' 

 egg-cell. The nucleus of the 



ovum during the quiescent stage lies near the center of 

 the cell, but gradually moves toward the cell-wall as the 

 egg becomes more mature. During the final stages in the 

 development of the egg, the nucleus loses a large part of 

 its chromatin. This process is called maturation and re- 

 sults .ultimately in reducing the number of chromosomes to 

 one-half the number characteristic of the species. This 

 process is preparatory to the fertilization of the egg by 

 the spermatozoon. During fertilization, the chromo- 



