ACCOUNT OF THE GERM-CELL CYCLE 43 



tion, and as shown in Fig. 9 these divisions result 

 in the production of four functional spermatozoa 

 in the male, and one functional egg and three polar 

 bodies (abortive eggs) in the female. This increase 

 in the number of cells is not, however, the most im- 

 portant phase of the maturation process, since a 

 large part of our knowledge of the physical basis of 

 heredity has been derived from studies of the be- 

 havior of the chromatin at this time. This subject 

 will be dealt with more fully in Chapter IX, and 

 for the present only a brief account of events need 

 be given. 



The first thing to be noted is that the mitoses 

 leading to the division of the germ cells during mat- 

 uration differ from those of ordinary cell multiplica- 

 tion. The germ cells, when they are ready for the 

 maturation divisions, are known as primary oocytes 

 and primary spermatocytes. The nuclei of these 

 cells possess the complete or diploid number of 

 chromosomes, characteristic of somatic cells ; but 

 after maturation the eggs and spermatozoa con- 

 tain only one-half of the original diploid number, 

 or the haploid number. These mitoses are conse- 

 quently called reducing or meiotic. The details of 

 these mitoses differ in male and female germ cells 

 and in different species of animals. 



During and at the close of the growth period in the 

 male the chromatin granules form a spireme which 

 condenses at one side of the nucleus, a condition 

 known as synizesis. After a time the spireme 

 again spreads throughout the nucleus, but is now 



